Chapter 20. Pediatric Applications

The role of point-of-care ultrasound in the emergent care of ill and injured pediatric patients continues to evolve and mature. Ultrasound technology is ideally suited for infants and children as it allows real-time visualization of anatomic structures without causing pain, requiring sedation, or exposing developing tissues to ionizing radiation.

There are numerous indications for emergency ultrasound common to both adult and pediatric emergency care. This has led to a greater understanding of the differences that exist when the same applications are used for both pediatric and adult patients. In addition, the functionality of emergency ultrasound has been further expanded by recent innovation and the development of several pediatric-specific applications.

Trauma remains one of the leading causes of morbidity and mortality in children. In the United States, traumatic injuries result in hospital admission for approximately 600,000 children each year.1 In the pediatric age group, blunt trauma is more prevalent than penetrating trauma, and 20–30% of pediatric trauma cases involve the abdomen.2

The history and physical examination form the foundation of the patient evaluation; however, they may be difficult to obtain in children who have altered mental status, CNS trauma, or distracting injuries. In one study of children with blunt abdominal trauma, an initial physical examination was considered reliable in only 41% of cases.3 Furthermore, the exam may be misleading in up to 45% of injured children.4,5

The use of ultrasound in pediatric trauma with the focused assessment with sonography for trauma (FAST) examination has increased over the past decade, but it has not been as well accepted or widely used as it has for adult trauma care. In a survey of general emergency physicians, pediatric emergency physicians, and trauma surgeons, 91% of the respondents considered abdominal ultrasound to be “somewhat to extremely useful.”6 However, with regard to pediatric trauma patients, 73% of all respondents considered abdominal ultrasound to be useful, while only 57% of pediatric emergency physicians considered it so. Furthermore, only 14% of pediatric emergency physicians routinely use abdominal ultrasound for evaluation of their trauma patients.6

Numerous advantages exist for using ultrasound in pediatric trauma, mirroring its benefits in adult trauma (see Chapter 5, “Trauma”). In pediatrics, limiting the exposure of ionizing radiation is especially appealing.7 The results of a large prospective multicenter trial were recently reported, and showed that pediatric trauma patients with a low-to-moderate clinical suspicion for intra-abdominal injury were significantly less likely to undergo abdominal CT scanning if they underwent a FAST exam.8

Clinical Considerations

The 1980s saw a transition away from diagnostic peritoneal lavage toward the use of abdominal CT. CT is still the most commonly used modality in evaluating pediatric abdominal injuries.9–18 The primary advantage of CT is that it accurately and reliably identifies and characterizes most intraperitoneal and retroperitoneal injuries. A major disadvantage of CT is that it exposes patients to significant doses of ionizing radiation. Children are 10 times more sensitive to the induction of cancer than adults, and one study estimates that a single abdominal CT in a young girl results in a risk of fatal cancer later in life of approximately 1 in 1,000.19 Some physicians have questioned the widespread use of CT and advocate the use of ultrasound for screening pediatric blunt trauma patients.20–22

The FAST examination is a noninvasive diagnostic tool for detecting hemoperitoneum, hemopericardium, and hemothorax (Figure 20-1).6 A systematic review assessed 25 studies consisting of 3838 children undergoing abdominal ultrasound after sustaining trauma. All studies were observational and the methodology, ultrasound protocols, and outcome definitions were all highly variable. The meta-analysis showed that the FAST exam had a sensitivity of 80% for identifying hemoperitoneum.23 The sensitivity fell to 66% when patients with intra-abdominal injuries, but without hemoperitoneum, were included.23 Over one-third of pediatric solid organ injuries are not associated with free intraperitoneal fluid,26,27 and failure to identify patients with intra-abdominal injury without hemoperitoneum is a known limitation of the abdominal ultrasound examination and is not considered a reasonable outcome measure for FAST by most providers.26,28

A prospective observational study evaluated the test characteristics of the FAST examination to detect any amount of fluid as well as clinically significant fluid in pediatric patients who suffered blunt abdominal trauma.24 Test characteristics for detection of significant intra-abdominal fluid show a sensitivity of 52% and a specificity of 96%. Clinically significant fluid was defined as moderate free fluid on abdominal CT scans or if patients went directly to the operating room for intra-abdominal injury. When evaluating the test characteristics of the FAST for detection of any intraperitoneal fluid the sensitivity dropped to 20%, while the specificity remained high at 98%. These data suggest that the FAST exam is useful when positive; however, when it is negative, it does not exclude the presence of intra-abdominal injury.

The clinical utility of the FAST exam as a screening tool that can potentially decrease the use of CT is not addressed in the pediatric trauma literature. But as in adults, the FAST exam is very sensitive for hemoperitoneum in pediatric patients who are hypotensive as the result of intraperitoneal blood loss.25

The E-FAST or “extended” FAST examination includes evaluation of the lungs for pneumothorax. Use of the E-FAST examination has been well established in adults (see Chapter 5, “Trauma”). Ultrasound evaluation for pneumothorax has been shown to be more sensitive (98%) than a supine chest radiograph (76%) in adult trauma patients, when compared to CT as the gold standard.29 A case report from a neonatal special care nursery had a similar finding.30 The E-FAST examination can be performed at the bedside in 3 minutes or less31,32 and is easily repeatable.

Clinical Indications

An extended point-of-care ultrasound examination is indicated in children with:

• Significant abdominal or thoracic trauma
• Patients with unexplained hypotension
• Patients with altered mental status

Significant Abdominal or Thoracic Trauma

A complete E-FAST exam should be performed on all pediatric patients with significant blunt or penetrating thoracoabdominal trauma as part of the secondary survey. In hemodynamically unstable pediatric trauma patients, the E-FAST examination may rapidly identify an abdominal or thoracic source of hypotension and assist with decision making regarding timing of diagnostic testing versus operative intervention. The abdominal portion of the E-FAST exam has the best test performance in children who are hemodynamically unstable with significant hemoperitoneum.25 If free intraperitoneal fluid is identified, and the patient remains hypotensive after a bolus of IV fluid, the decision to perform exploratory laparotomy should be considered. If the patient stabilizes with a fluid bolus, abdominal CT scanning may be considered to guide selective laparotomy.

The E-FAST examination may also allow for prioritization of imaging studies in hemodynamically stable patients after initial evaluation and resuscitation. Patients with positive E-FAST examinations are typically triaged to abdominal CT with greater expediency than those patients with normal E-FAST examinations. E-FAST may also be useful in evaluating alert, hemodynamically stable pediatric trauma patients without abdominal tenderness, who would otherwise not routinely undergo abdominal CT, and who may occasionally have intra-abdominal injuries.

In hemodynamically stable patients, the information provided by a negative E-FAST examination may be sufficient for the clinician to decide against abdominal CT.8,23 It may be prudent to admit such patients for observation and serial ultrasound and physical exams. Patients who are hemodynamically stable and have a negative E-FAST examination should undergo abdominal CT scanning if they demonstrate peritoneal signs, abdominal distention, seat belt abrasion, hematuria, or persistent tachycardia.

The E-FAST examination is also indicated in pediatric patients with penetrating trauma. The main benefit of using the E-FAST exam in penetrating thoracoabdominal trauma is not necessarily to rule out injury and avoid CT scanning, but to quickly identify which body cavity is injured to guide the sequence of surgical exploration or management.

Anatomical Considerations

The FAST examination was designed to assess the three primary dependent areas of the peritoneal cavity (right upper quadrant, left upper quadrant, and pelvis) along with the thoracic cavity. The location of the fluid depends primarily on the source of the bleeding, but may be affected by the position of the patient. For the purpose of understanding the anatomy as it relates to the FAST examination, the abdomen is divided into quadrants by the mesentery of the transverse colon horizontally and by the spine vertically (see Figure 5-6A). Relevant anatomy needs to be identified in order to evaluate for surrounding intra-abdominal, thoracic, or pericardial fluid. There are some pediatric considerations, which are discussed below.

In the right upper quadrant, Morison's pouch is the potential space between the liver and the right kidney and represents the most dependent supramesocolic area. Blood from a liver laceration will accumulate in this area; blood from a splenic injury may also spill over the lumbar spine into Morison's pouch. Blood from an inframesocolic injury can spread over the sacral promontory into Morison's pouch as well via the right paracolic gutter. Since most major blunt abdominal injuries involve the liver and spleen, the view of Morison's pouch is regarded as the most important of the four views in the FAST examination in adults.33 Alone, it has been found to be 51–82% sensitive in detecting free fluid.34–36 In pediatric patients, however, free fluid tends to accumulate in the pelvis.37

Blood from a splenic injury will accumulate first in the left subphrenic space. There is no equivalent of Morison's pouch as the splenorenal ligament attaches the spleen and kidney. Therefore, intraperitoneal fluid accumulates circumferentially around the spleen: commonly below the diaphragm, at the inferior pole of the spleen, and less so in the splenorenal fossa. Blood from this area can flow into Morison's pouch, and will preferentially reach the pelvis by spilling down the right paracolic gutter because the left upper quadrant is separated from the left paracolic gutter by the phrenicocolic ligament.38

Blood from inframesocolic injuries will accumulate first in the rectovesicular pouch in boys and the retrouterine pouch of Douglas in girls. These areas are the most dependent portions of the peritoneal cavity.38 One study found an isolated pelvic view to be 68% sensitive in detecting free intraperitoneal fluid.34 In children, the pelvis view is the region most likely to be positive if a patient has intra-abdominal free fluid due to an isolated liver or spleen laceration.37

Ultrasound examination of pneumothorax is based on observation of sliding of the visceral pleura of the lung on the parietal pleura of the chest wall. In a supine trauma patient, thoracic air tends to accumulate between the anterior chest wall and the lung, separating the parietal and visceral pleurae.

The classic FAST view of the heart is the subxiphoid view. In children, this view may be limited due to air in the stomach, from crying, or from bag mask ventilation. If the subxiphoid view is insufficient, consider the parasternal long-axis view of the heart. This view will visualize the right and left ventricles, left atrium, aortic and mitral valves, the pericardium, and the descending aorta. The descending aorta is the landmark used to differentiate pericardial from pleural effusions posterior to the heart.

Technique and Normal Ultrasound Findings

The FAST examination of pediatric patients consists of subxiphoid, right and left upper quadrant, and suprapubic views, which are identical to those in adults (Figure 20-2; Video 20-1: Pediatric Considerations). The E-FAST examination adds bilateral lung views to assess for pneumothorax. Views of the hemidiaphragms and caudal thorax, to assess for hemothorax, should be obtained with the right and left upper quadrant views. Use a low-frequency transducer between 2 and 6 MHz (includes the phased-array transducer and curvilinear or convex transducers) in children. Phased-array transducers are preferred for younger children as the flat, small footprint allows for better imaging between the ribs. Some authors recommend using a 5.0 MHz (or even 7.5–10 MHz) transducer for finer resolution.21,39 The E-FAST examination should be performed with the patient supine, which is how the patient is transported on a backboard after blunt trauma. By convention, the index marker on the transducer should be directed cephalad or to the patient's right. Move the transducer up or down one or more rib spaces to optimize the view.

Splenic or hepatic injuries account for 74% of cases of hemoperitoneum in pediatric blunt trauma.40 With the index marker cephalad, place the transducer in a coronal plane in the mid to anterior axillary line at the 10th intercostal space or below (Figure 20-3). The kidney lies retroperitoneal, so direct the transducer dorsally to maximize the view of the liver–kidney interface. Rotate the transducer counterclockwise and align it with the intercostal space to minimize shadowing. Sliding or tilting the transducer cephalad brings the lower thorax into view, displaying the mirror image artifact of the liver above the diaphragm (Figure 20-4).

Visualize the diaphragm superiorly and the tip of the liver inferiorly. Scan the inferior pole of the kidney to assess for free intraperitoneal fluid in the right paracolic gutter. Visualization of the inferior pole of the liver is necessary since free fluid may accumulate there before progressing to Morison's pouch (Figure 20-5).

The goal of the left upper quadrant view is to examine the potential space around the spleen, between the spleen and the diaphragm, and around the inferior pole of the spleen. With the index marker cephalad, place the transducer in the posterior axillary line in the coronal plane at the 9th intercostal space or below (Figure 20-6). Rotate the transducer clockwise and align it with the intercostal space to minimize rib shadows. Inspect the lower left thorax for intrathoracic blood, as described above. Visualize the diaphragm superiorly and the lower pole of the spleen inferiorly (Figure 20-7). Scan the inferior pole of the left kidney to evaluate for intraperitoneal fluid in the paracolic gutter.

Scan the pelvis for free intraperitoneal fluid with both transverse and sagittal views. The bladder is used as a landmark to evaluate for hemoperitoneum. Intraperitoneal fluid accumulates cephalad and posterior to the bladder. Ideally, scan the suprapubic view prior to insertion of a Foley catheter. Urine in the bladder provides an important acoustic window. Place the transducer just cephalad to the symphysis pubis in the midline sagittal plane with the index marker cephalad and in the transverse plane with the index marker to the patient's right (Figure 20-8). Urine appears hypoechoic or anechoic and is well circumscribed by the bladder wall (Figure 20-9). The uterus in girls and prostate in boys can be seen posterior to the bladder. The transition in tissue densities between urine in the bladder and the surrounding soft tissue can produce bright echoes, so reducing the far gain will enhance subtle soft tissue details and help avoid missing free fluid in this area.

Obtain a midline sagittal view first to get an overview of the pelvic anatomy. In the midline sagittal view, the posterior angle of the bladder divides the intraperitoneal space containing the bowel (and the uterus in girls) from the pelvic structures (prostate and seminal vesicles in boys, vagina in girls) (Figure 20-10). Free intraperitoneal fluid only accumulates cephalad (to the left) to the posterior angle of the bladder, so it is an important anatomic landmark to recognize.

The amount of free intraperitoneal fluid that can be reliably detected in children has not been studied. In adults, 400 mL is a reasonable estimate.41,42 One study suggests that placing the patient in Trendelenburg or decubitus positions allows for the detection of intraperitoneal fluid with only two-thirds of the amount of fluid required in the supine position.43 The reverse Trendelenburg position may help with identification of pleural or pelvic free fluid.

Always begin the FAST examination with the subxiphoid view of the heart for penetrating trauma patients in whom cardiac injury is suspected. Place the transducer in the subxiphoid region in the coronal plane with the index marker to the patient's right. Direct it toward the left shoulder at a steep angle (relative to the abdominal skin) using the liver as an acoustic window (Figure 20-2). This provides a four-chamber view of the heart surrounded by a hyperechoic pericardium (Figure 20-11). In the crying child, slide the transducer laterally, slightly to the right of the midline, to avoid the air in the stomach by using the liver as an acoustic window. If this view is insufficient, consider the parasternal long-axis view. Place the transducer along the axis of the heart from the right shoulder to the left hip. This approach will visualize the right and left ventricles, left atrium, aortic and mitral valves, as well as the pericardium surrounding the heart and the descending aorta. The descending aorta is the landmark used to differentiate pericardial from pleural effusions.

Perform the lung ultrasound examination with a linear transducer or any transducer with a higher frequency selected. Place the transducer in a longitudinal orientation with the hyperechoic ribs as landmarks on either side of the image. Decrease the depth to optimize the view of the pleural interface. Rapidly assess both sides of the chest for the presence or absence of lung sliding by scanning in the midclavicular line in the second or third intercostal space bilaterally. The interface of the visceral and parietal pleura is a thin line just deep to the ribs and appears bright and echogenic (Figure 20-12). Pleural sliding is seen in real time as scintillating, to-and-fro movement at the level of the pleural line. If pleural sliding is not obvious, observe the pleural line for at least three respiratory cycles and examine other sites on the chest wall. M-mode or color Doppler is commonly used to help assess and document pleural movement (Figure 20-13, and also see Chapter 5, “Trauma”). When evaluating the lungs in infants and toddlers, the pleura may be visible through the ribs (as a continuous hyperechoic line) because the ribs are primarily cartilage (Figure 20-14). In younger children, the ribs produce anechoic shadows but they are not as strong as the rib shadowing in adolescents and adults because the ribs are not yet completely ossified (Figure 20-15).

Common and Emergent Abnormalities

Hemoperitoneum

A small amount of intraperitoneal fluid may be visible just at the inferior portion of the liver, whereas a large amount of fluid will separate the liver from the kidney and produce a thick anechoic stripe in Morison's pouch (Figure 20-16,B). Blood most often accumulates circumferentially around the spleen and below the left diaphragm because the splenorenal ligament maintains the integrity between the spleen and the kidney (Figure 20-17). Nonclotted blood in the pelvic region appears as anechoic free fluid posterior and cephalad to the bladder in boys (Figure 20-18A) and both anterior and posterior to the uterus in girls (Figure 20-18B).

Hemopericardium

Unclotted blood in the pericardial space will appear as an anechoic stripe lying between the two brightly, echogenic layers of the pericardium (Figure 20-19). Clotted blood is more complex and echogenic. Small pericardial effusions may be visible anteriorly, posteriorly, or at the apex so it is important to scan through all of these areas, especially in patients who may have a penetrating cardiac injury (Figure 20-20).

Hemothorax

Blood in the chest appears as an anechoic area cephalad to the hemidiaphragm (Figure 20-21), and eliminates the mirror artifact. A large left sided hemothorax can sometimes be seen behind the heart on cardiac views (Figure 20-20).

Pneumothorax

Absence of lung sliding, visualization of a lung point, and the “stratosphere” sign with M-mode may be seen when a pneumothorax is present (Figure 20-22). The lung point is the transition point between the pneumothorax and the normal lung and is highly specific for a pneumothorax. Absence of color Doppler scanning and linear, laminar lines deep to the pleura in M-mode resembling those of the overlying stationary anterior chest wall supports the diagnosis of pneumothorax (see Chapter 5, “Trauma,” for additional examples).

Common Variants and Selcted Abnormalities

Certain aspects of normal anatomy can be easily mistaken for positive findings. In the upper quadrant views, dark rib shadows must not be interpreted as anechoic blood. Since all fluid appears black (anechoic) on ultrasound, bile in the gallbladder and blood in the inferior vena cava (IVC) or aorta can be erroneously interpreted as free intraperitoneal fluid. In each of the abdominal views, and especially in the suprapubic view, fluid-filled loops of bowel can be mistaken for free intraperitoneal fluid.28 Holding the transducer still and observing for peristaltic movements often help differentiate free fluid from intraluminal fluid.

Perinephric adipose tissue, which may be present in pediatric patients of all ages, may be hypoechoic relative to surrounding structures and can be mistaken for free fluid or clotted blood. Comparison with the area around the other kidney may help distinguish this normal variant; additionally, perinephric fat does not move separately from the kidney with respirations and is more homogenous than clotted blood.

A subcapsular hematoma may be visible between the bright reflection of the splenic capsule and the homogenous parenchyma, which may be disrupted by injury. Blood is often clotted, appearing more echogenic, but may be distinguished from the splenic parenchyma. Intraparenchymal blood is often isoechoic with the splenic parenchyma on initial evaluation.44 Over time, a hematoma will become primarily hypoechoic.

Ascites is rarely an issue in children, and free fluid identified in the chest or abdomen in an injured child is regarded as blood until proven otherwise.

Pitfalls

1. There is no contraindication to performing an E-FAST exam unless it interferes with more important diagnostic tests or urgent patient management. Subcutaneous emphysema, gas-filled bowel, or morbid obesity may render the examination indeterminate.

2. The E-FAST examination is one data point in a continuum of clinical decision making. Repeat exams are often very helpful.

3. The E-FAST examination may not detect all intraperitoneal bleeding or significant injury. CT is generally used to characterize significant abdominal injuries, but most injuries will be managed nonoperatively in children.

4. Air scatters sound waves and makes images difficult to interpret. The inability to obtain standard views should raise the suspicion for free air or subcutaneous air.

5. Subtle free fluid may be missed if care is not taken to identify all the potential spaces. The view of Morison's pouch is generally the easiest to identify and interpret. In children, however, this view is often more caudad than in an adult. In the left upper quadrant view, clinicians often fail to place the transducer far enough posteriorly. The perisplenic region is also more cephalad than Morison's pouch. Missed subcapsular hematomas and blood between the spleen and the diaphragm are often the causes of false-negative scans; so it is recommended that at least 50% of the left hemidiaphragm be visualized to avoid missing blood in this area.

6. The pelvic views yield the most errors.28,45,46 A bladder containing little urine provides a poor acoustic window. The introduction of normal saline, in quantities appropriate for the patient's age, into the bladder through a Foley catheter may be necessary to obtain good pelvic images. Also, care should be taken not to confuse free fluid with iliac vessels or other anechoic structures in the pelvis (Figure 20-23).

7. Adequate visualization of the heart in the subxiphoid view can be challenging, especially when the child is obese, crying, tachypneic, or has abdomen tenderness. Flattening the angle of the transducer and having the patient inspire may bring the heart into view. Another option is to move the transducer laterally toward the liver using the liver as an acoustic window. If adequate visualization is still not possible, a parasternal long- or short-axis view of the heart is recommended.

Case Study

Patient Presentation

A 3-year-old healthy girl was transported to the ED by EMS after collapsing in her home. Her mother stated the girl came inside from playing in the yard and said, “Ow. Mommy, help,” and then fell to the ground. Her mother called 911 immediately. Per EMS the girl had altered mental status on scene and a serum glucose of 200 mg/dL. She was noted to be tachycardic and hypotensive.

Upon arrival, she had a blood pressure of 70/40 mm Hg, heart rate 150 beats per minute, respiratory rate 40 per minutes, and an oxygen saturation of 98% on room air. Her mental status waxed and waned, but she opened her eyes to painful stimuli. She had an unremarkable physical exam with no signs of trauma. Her abdomen was soft but moderately tender to palpation. Her repeat blood glucose was 500 mg/dL.

Management Course

Access was established with intraosseous needles in both tibias and the team prepared to intubate the patient due to worsening vital signs and deteriorating mental status. An E-FAST exam was performed and revealed a small amount of free fluid at the inferior portion of the liver and a large amount of fluid in the pelvis (Figure 20-24). The remainder of the E-FAST exam revealed normal lung sliding (no pneumothorax) and mirror artifact above the diaphragm (no hemothorax) bilaterally. The cardiac exam revealed a hyperdynamic heart and no pericardial effusion. Surgery was immediately consulted. A repeat E-FAST 5 minutes later revealed free fluid accumulating in Morison's pouch as well as the pelvis (Figure 20-25). The patient was taken to the operating room, where the surgical team found a liver laceration and controlled the bleeding.

Commentary

This case demonstrates the utility of the E-FAST exam in young children with altered mental status, abnormal vitals signs, and no history or evidence of trauma. This patient could have been mismanaged as a patient with presumed diabetic ketoacidosis had it not been for the identification of hemoperitoneum. Emergency ultrasound rapidly revealed the cause of her hypotension and directed her care appropriately to surgical intervention. Given that she was too unstable for a CT scan, emergency ultrasound was the only appropriate imaging modality.

The role of neuroimaging for pediatric patients presenting to the ED after a closed head injury continues to evolve. Ultrasound has become an attractive alternative to skull radiographs and CT for imaging the skull, as it is rapid, reliable, inexpensive, and without ionizing radiation.

Clinical Considerations

The identification of an intracranial injury is critical to minimize morbidity and potential mortality. Pediatric patients, especially younger children, with intracranial injury may be asymptomatic on clinical exam.47 However, the presence of a scalp hematoma in asymptomatic infants with a head injury is predictive of skull fractures, which are in turn predictive of intracranial injury.48

Ultrasound has been shown to be an effective modality to identify skull fractures in a porcine model, with an accuracy of 97%.49 A recent case series highlighted the clinical value of this same technique in pediatric patients.50 The authors suggested three potential roles for emergency ultrasound: replacement of skull radiographs, rapid identification of a skull fracture prompting expedited management, and ruling out a skull fracture, hence potentially eliminating the need for CT. Further study is needed to fully assess the characteristics of this application and its integration with validated age-specific prediction rules.

Clinical Indications

An emergency ultrasound is indicated in stable pediatric patients with a scalp hematoma in whom the identification of a skull fracture will prompt further imaging or change clinical management.

Anatomical Considerations

The cortex of the skull appears as a hyperechoic curvilinear line under the normal scalp soft tissue appearance (Figure 20-26). When overlying soft tissue edema is present, it will have a heterogeneous sonographic appearance that disrupts the normal fascial architecture.

Getting Started

The presence of a skull fracture can be accurately identified with the patient in any position. For this reason, place the patient in a position of comfort, such as a caregiver's lap, in order to decrease anxiety and facilitate image acquisition. Rarely the head may need to be gently restrained. Use copious amounts of gel to minimize painful contact with the hematoma and to maximize image quality. Warm gel may also be beneficial in keeping the patient comfortable and calm throughout the exam.

Technique and Normal Ultrasound Findings

The ideal transducer for this application is a high-frequency linear array transducer. The transducer is placed over the area of swelling and scanned in two orthogonal planes (Figure 20-27). The cortex should appear continuous with the exception of the cranial sutures and fontanelles.

Common Abnormalities

A scalp hematoma will be identified as a distinct, homogenous hypoechoic area adjacent to the cortex (Figure 20-28). A skull fracture appears as a hypoechoic break in the contour of the hyperechoic skull (Figure 20-29). The fractured bone may appear inline or depressed depending on the character of the fracture. Comparison with the opposite side of the skull can help to distinguish cranial sutures from linear fractures.

Pitfalls

1. The sensitivity and specificity of ultrasound to detect skull fractures are currently unknown. Although this application has been demonstrated to be effective in case series, its limitations have yet to be fully documented. Care should be taken when using this application for clinical decision making.

2. Cranial sutures may be misidentified as fracture. Understanding the position and normal appearance of the cranial sutures is needed to correctly distinguish pathology. Normal cranial sutures may have an end-to-end, beveled, or overlapping appearance.51 (Figure 20-30, Figure 20-31) A fracture or injury along a suture line must also be considered with a hematoma overlying a cranial suture and interpreted within the context of the clinical scenario.

Case Study

Patient Presentation

An 8-month-old baby boy presented to the ED after a fall from his highchair onto hardwood floor 1 hour prior to admission. The mother saw the boy fall and strike the right side of his head on impact. She denied loss of consciousness, vomiting, or abnormal behavior since the fall. His blood pressure was 90/60 mm Hg, heart rate 90 beats per minute, respiratory rate 26 per minute, and an oxygen saturation of 100% on room air. The patient was alert and appropriate, with normal tympanic membranes and no Battle's sign. He had a hematoma in the right temporoparietal area measuring 3 × 3 cm. Palpation of the underlying skull was limited due to pain and significant swelling at the site. The exam was otherwise normal.

Management Course

An emergency ultrasound confirmed the absence of a skull fracture under the area of swelling. The patient was appropriately observed in the ED and then discharged home with return precautions.

Commentary

This case demonstrates the advantage of using emergency ultrasound to assess for skull fracture in closed head trauma. Unnecessary imaging and radiation exposure can be avoided.

Intraosseous access is widely used in the emergent resuscitation of pediatric patients. This life-saving technique allows for rapid fluid resuscitation and the administration of medications when peripheral IV access cannot be achieved.52 The traditional role of the intraosseous needle (ION) has been further expanded by automated technologies that facilitate its insertion. In addition, the ION is increasingly used in the prehospital setting53 as well as in the resuscitation of neonates.54

Clinical Considerations

A misplaced ION can create confusion and delay the delivery of essential fluids and medications during resuscitation. Although serious complications are rare,55 they include extravasation of fluid, compartment syndrome, and muscle necrosis.56 Conventional methods used to confirm needle position may be unreliable. These methods include observing a bone marrow aspirate, the presence of blood on the tip of the needle stylet, the ION standing firmly upright, and the ability to infuse fluid easily without visible extravasation or swelling. Based on current experience, ION confirmation by ultrasound is feasible and can be rapidly performed during resuscitation.57 Ultrasound confirmation of ION placement ensures reliable delivery of the therapeutic agents while minimizing the risk of complications from a misplaced needle.

Clinical Indications

All patients with an ION placed in the ED or in the prehospital setting should undergo ultrasound confirmation to ensure correct needle position. Patients transferring from one ED to another are at risk of having an ION dislodged during transport. They should have needle position determined on arrival and while en route if possible. Patients with ongoing resuscitative efforts, which rely on an appropriately positioned ION, should have needle position confirmed on a serial basis to ensure continued efficacy.

Anatomical Considerations

The cortex of the target long bone should appear as a hyperechoic linear structure present below the heterogeneous soft tissue (Figure 20-32). The hyperechoic character of the cortex increases as the bone matures. For this reason, an older patient's cortex appears more distinct than a younger patient's cortex (Figure 20-33).

Getting Started

The majority of ION confirmation occurs during resuscitation. Therefore, preparation is key as it minimizes disrupting the tasks of other team members. The ultrasound system should have preestablished settings, gel on the transducer, and a location at the bedside that is predetermined. A system preset for ION confirmation further improves efficiency by limiting the time needed to acquire adequate images.

Technique and Normal Ultrasound Findings

The ideal transducer for this application is a high-frequency linear array transducer, although needle confirmation may be determined with a variety of transducer types and frequencies. The transducer is placed proximal or distal to the ION in the transverse plane and the accessed long bone is then visualized in a short-axis view (Figure 20-34,C).58 The transducer may also be positioned in a sagittal or longitudinal plane, which enables visualization in the long-axis.

Color or power Doppler may be used to identify flow below the cortex of the target site and within the bone marrow (Figure 20-34B,D). An initial 5–10 mL flush given following ION insertion can be recognized using color Doppler. Serial examinations to monitor ongoing fluid or medication infusions may require the low flow velocity sensitivity of power Doppler.

Common Abnormalities

The identification of flow in the soft tissue and not in the marrow suggests a misplaced ION. Extraosseous flow in the soft tissue may appear between the cortex and the transducer or outside the lateral margins of the target long bone (Figure 20-35, Figure 20-36).

Common Variants and Other Abnormalities

There is a theoretical risk of bony fracture or a partially placed ION. Although not reported in the literature, it is possible that flow could be present both within the marrow and in the soft tissue in both these scenarios. If recognized, an alternative site of access would be preferred to ensure proper fluid and medication delivery.

Pitfalls

1. Care should be taken while scanning the ION to reduce the risk of dislodging the needle during the ultrasound scan. The ION should be appropriately secured and efforts made not to bump the transducer against the needle.

2. A higher probability of error may exist when scanning with the transducer in sagittal or longitudinal view. Long-axis visualization of the cortex can lead to erroneous interpretation of flow due to inadvertent visualization off axis or visualization of the fibula.57

3. Low velocity flow should be considered if color Doppler fails to identify any flow during the initial manual push or subsequent infusion. A color Doppler scale adjustment or the use of power Doppler may be necessary to correctly assess needle position in this setting.59

4. A single determination of needle placement during resuscitation may not be adequate to ensure ongoing efficacy of the ION. The potential for needle dislodgement as a result of inadvertent movement may occur at anytime during the resuscitation. Serial examinations may be required.

Case Study

Patient Presentation

A 6-month-old female child with a history of developmental delay, seizure disorder, and a gastric tube presented to the ED with 48 hours of severe vomiting and diarrhea. She had no urine output for 6 hours and had become increasingly lethargic despite ongoing hydration through the gastric tube.

Her initial blood pressure was 68/40 mm Hg, heart rate 200 beats per minute, respiratory rate 60 per minute, temperature 37.0 C, and an oxygen saturation of 96% on room air. The patient was minimally responsive to voice, mucous membranes were dry, and her eyes were sunken. Capillary refill was 3 seconds. There was severe diaper dermatitis on the buttocks. Large volume diarrhea was ongoing during the examination without blood or mucous.

Management Course

Two attempts to place peripheral IV access failed and an ION was immediately placed in the right tibia. No marrow or blood was aspirated following insertion. The ION was upright and appeared to be infusing without visible soft tissue swelling. The ION was secured and emergency ultrasound immediately confirmed correct needle placement by identifying flow within the marrow using color Doppler. Aggressive IV rehydration was immediately started and vital signs normalized.

Commentary

This case demonstrates the importance of fast and accurate ION placement in resuscitation. Emergency ultrasound confirms needle placement while conventional methods of confirmation prove unreliable. Hypovolemic shock can then be treated aggressively.

Acute appendicitis is the most common surgical emergency in children. The diagnosis is made in 60,000–80,000 children each year in the United States and accounts for 0.6% of pediatric ED visits.60–64 While the appendix has appeared in anatomic texts for hundreds of years, the linkage with an acute inflammatory process was first noted in 1711 by Heister, followed by the intervention of an appendectomy by Melier in 1827.65 The incidence of appendicitis is highest in the adolescent years, which correlates closely with the peak amount of lymphoid tissue present within the GI tract.66 Appendicitis is thought to result from luminal obstruction by lymphoid hyperplasia, fecal impaction, or appendiceal calculi. The lumen subsequently distends, leading to venous congestion, wall ischemia, and bacterial translocation. Uncorrected this may lead to perforation, abscess formation, or peritonitis in 36–48 hours67; however, there are reports of spontaneously resolving appendicitis.68–70

Delays in diagnosis have been associated with higher rates of perforation and an increase in the rate of overall morbidity from 6% to 36%.71 Studies of preschool-aged children report a perforation rate of 30–60% at laparotomy,72–74 with 100% perforated when aged 3 and under.75 If the diagnosis is delayed, the perforation rate increases to 65% or higher, and mortality increases as well.76 Failure to diagnose appendicitis is one of the most frequent malpractice claims against emergency physicians.77–79 In pediatric patients, the diagnosis is often elusive for even the most astute clinician, with misdiagnosis rates up to 100% in infants, 57% for toddlers, 28% for school aged children, and 15% for adolescents.80

Clinical Considerations

Acute appendicitis should be considered in any patient with right lower quadrant abdominal pain, nausea, vomiting, anorexia, and fever. Together, these signs and symptoms have been found to be highly sensitive for appendicitis.81 However, children are often unable to adequately express themselves and the physical examination may be nondiagnostic. Children with equivocal findings represent 25–30% of all cases of acute appendicitis.82,83 Although frequently ordered, the WBC count84 and plain abdominal radiograph85,86 are neither sensitive nor specific for appendicitis and have a low positive likelihood ratio.87 Because of these limitations, negative laparotomy rates as high as 20% have been reported, with rates of 10–15% accepted historically.88–90 Negative laparotomies come at significant costs, both financially and in terms of morbidity. Morbidity includes adhesions, prolonged or return hospitalization, and time away from school.

Clinical scoring models have been proposed to identify patients who may appropriately receive surgical intervention without diagnostic imaging. Two studies proposed scoring models based on common clinical and laboratory features, with respective sensitivities of 75% and 100% and specificities of 84% and 92%.91,92 However, attempts to validate these models in other settings have been unsuccessful.93–97 A low-risk clinical screening model showed that patients with a low absolute neutrophil count, no nausea, and no right lower quadrant tenderness have a very low risk of appendicitis, but this model does not apply to most patients.98 As would be expected, patients who score at the extremes of these models pose little diagnostic dilemma. These studies, however, highlight that there are many patients with equivocal signs and symptoms who need diagnostic imaging.

Currently, ultrasound and CT are commonly used to help diagnose acute appendicitis in patients with equivocal presentations. The first demonstration of an inflamed appendix by ultrasound was reported in 1981.99 Development of the graded compression examination in 1986 established a technique and criteria for the diagnosis of appendicitis.89

The right lower quadrant examination of appendicitis is one of the more technically difficult ultrasound examinations. Studies of ultrasound use in children for detecting appendicitis have sensitivities ranging from 44% to 98% and specificities from 88% to 100%.62,89,100–110,238 The wide range of sensitivity reflects the operator-dependent nature of ultrasound, particularly for this examination. This is again demonstrated by the wide range of normal appendix visualization rates, from 2% to 99%.62,125

Nonradiologists have also looked at employing right lower quadrant sonography in their evaluation of acute appendicitis. Emergency physicians in Taiwan compared their evaluation of patients for appendicitis using ultrasound to the surgeons' clinical impressions without sonographic examinations and found sensitivities of 94.6% and 86.2%, respectively, for the diagnosis of appendicitis.111 Another study found a sensitivity of 65% and specificity of 90% utilizing primarily emergency medicine residents in the evaluation of appendicitis.112 Swiss surgeons achieved a sensitivity of 91% with ultrasound for detecting appendicitis.113 An investigation used “specially trained pediatricians” in addition to a pediatric radiologist and achieved 90% sensitivity.101

Studies of the use of helical CT for the diagnosis of appendicitis in children have produced sensitivities of 84–97% and specificities of 89–98%.62,102,109,110,240 Although these ranges of sensitivity and specificity overlap with those of ultrasonography, the reliability of sonography is less consistent. When CT and ultrasonography are compared directly, CT has been superior in each study,62,83,102,109,110,240 except for one study in which patients undergoing noncontrast CT were compared to a historic cohort who underwent graded compression sonography.110 In a meta-analysis comparing ultrasound to CT in children, there was no statistically significant difference found in the specificity, but with a significant difference in sensitivity of 6% in favor of CT.114

While CT has overall greater accuracy than ultrasound, there has been growing concern over the increased use of diagnostic imaging tests with ionizing radiation exposure.115–119 This is particularly troubling for pediatric patients, given the greater risks of children exposed to ionizing radiation.7,120–123 While rates of CT use have dramatically increased, the reduction in negative appendectomies or missed appendicitis remains unclear.115–118,124–126 To address this concern, several authors have analyzed maximizing the specificity of the ultrasound examination in proposing a staged algorithm for diagnostic imaging for acute appendicitis. One protocol utilizing ultrasound prior to CT reduced negative appendectomies from 14% to 4% and had an accuracy of 94%.62,127 Another study found that the implementation of a staged protocol reduced CT usage by 50% without an increase in morbidity.128 It is because of this safety and accuracy that the American College of Radiology has reaffirmed that the initial imaging modality for the evaluation of acute appendicitis in patients under 14 years remain graded compression ultrasonography, with CT reserved for equivocal or negative studies.129

MRI has also been utilized in selected patient populations, such as pregnancy, and found to be a potentially useful adjunct.130,131 When used in a general population sensitivities and specificities have been reported as high as 95–100%.132,133 The limitations of utilizing MRI in children would include cost, equipment, technician availability, and patient cooperation. Modern MRI protocols utilizing ultrafast spin echo sequences require 20 seconds of breath holding by the patient to minimize motion artifact.132 MRI could eventually replace CT for patients with equivocal or negative ultrasound studies, but further research is needed, since trials to date have been small.134,135

Clinical Indications

An ultrasound examination is indicated when there is clinical suspicion for appendicitis. It should be considered in a child with all or part of a constellation of symptoms that includes migratory right lower quadrant pain, vomiting, nausea, anorexia, pain with cough or hop, rebound tenderness, abdominal distention, or peritoneal signs.

Anatomical Considerations

The vermiform appendix is a hollow lymphoid organ whose function is not well understood. The blind-ended appendix typically arises from the cecum, 1–2 cm distal to the ileum in the right lower quadrant (Figure 20-37). It is rarely congenitally absent.136 The classic teaching is that the maximum pain from an inflamed appendix localizes to McBurney's point, at the midpoint of an imaginary line between the umbilicus, and the anterior–superior iliac crest. However, a 1933 study reported that the classic pelvic orientation of the appendix occurred in only 31% of 10,000 autopsies and retrocecal in 65%.137 Also, in a retrospective review on appendiceal positioning using ultrasound visualization, only 39% of patients with appendicitis had the appendix found in the classic mid-pelvic region, with 26% retrocecal.238

The appendix averages 6–9 cm in length, but it may be much longer. The normal diameter is <6 mm.67 From outer to inner, the appendiceal wall is composed of the serosa, muscularis propria, submucosa including the muscularis mucosa, and luminal mucosa. These layers are typical of the intestinal wall except that in the appendix the submucosa is heavily infiltrated with lymphoid tissue. The appendix is partially covered by a peritoneal fold known as the mesoappendix, which contains the appendicular artery, a branch of the ileocolic artery. The fold is often short, so the appendix may be folded or kinked.136

Technique and Normal Ultrasound Findings

Visualization of the normal appendix can be difficult and varies greatly with the patient and experience of the examiner (see discussion under Pitfalls, below).

A high-frequency linear array transducer is ideal for this application in children, while lower-frequency curved array transducers should be reserved for larger patients. Point the index marker cephalad or to the patient's right by convention. The graded compression technique is now the standard technique for the evaluation of appendicitis.89 Gradual, gentle compression with the transducer displaces gas and compresses bowel loops, improving visualization by eliminating artifacts caused by the bowel (Figure 20-38A,B). Adequate compression has been achieved when the landmark iliac vessels and/or psoas muscle are visualized.67 Since the appendix may lie in a variety of positions within the abdominal pelvic cavity, there is no single transducer position that provides consistent visualization.

There are two approaches for finding the appendix with ultrasound. First, in a patient with well-localized pain, the examiner may start in that patient-identified location.67 Alternatively, the examiner may scan the right lower quadrant in an organized fashion with the ultimate goal of distinguishing cecum from small bowel, and then to identify the appendix as it arises off the cecum. With the transducer in transverse plane along the lateral abdomen, the examiner should note the aperistaltic loops of ascending colon and progress caudad through the cecal fossa. Moving medially from the proximal cecum should bring the actively peristalsing loops of small bowel into view, as well as the psoas muscle and iliac vessels. Moving further medially across the psoas and iliac vessels brings the pelvic contents into view. Here, there is no structure to compress loops of bowel, so a filled bladder may also be used as a window into the pelvis. From the pelvis, move cephalad again along the medial psoas up toward the level of the umbilicus. Further evaluation of the cecal fossa with the transducer in the sagittal plane starting laterally and moving medial through the fossa over the psoas may help to identify and visualize the cecum and the appendix. Considering the frequency of retrocecal position of the appendix, use alternate coronal views (as needed) between the mid and anterior axillary line with the transducer sliding along the top of the iliac crest. The patient may need to be rolled into the left lateral decubitus position to optimize retrocecal imaging. These views may avoid gas shadowing from the air-filled cecum.

A normal appendix appears ovoid and may exhibit compressibility.138 Once the appendix is identified, measure the diameter from outer wall to outer wall in an anterior–posterior alignment perpendicular to the long axis. If the appendix appears ovoid in transverse view, measure at the narrowest segment.138 Trace the appendix from the origin off the cecum and document a blind-ending loop to ensure that the structure is not small bowel (Figure 20-39).

A noncompressible, nonperistalsing, tubular structure measuring ≥6 mm in anterior–posterior diameter is the most specific sign for acute appendicitis. While a normal appendix may measure >6 mm (Figure 20-40), one can exclude appendicitis with a smaller diameter. Note these findings on both the transverse and long-axis views. The transverse view gives a characteristic target-shaped appearance that may change with advancing disease. Luminal contents are variable and may appear collapsed, containing mucus, air, or some combination of both.

Common and Emergent Abnormalities

Appendicitis is diagnosed when the following findings are present (Figure 20-41):

• Target shape: Inflammation gives the appendix a classic targetoid or “bull's eye” appearance when viewed transversely. This results from anechoic fluid in the lumen, surrounded by an echogenic rings of mucosa, submucosa, and serosa separated by hypoechoic muscularis layers.139
• Diameter >6 mm: The diameter from outer wall to outer wall will be >6 mm due to inflammation.
• Noncompressible: Inflammation and appendicoliths prevent the appendix from compressing into an oval shape.
• No peristaltic activity: The appendix does not have peristalsis, as opposed to sometimes similarly appearing thickened small bowel.
• Periappendiceal inflammation: Acute appendicitis implies an active inflammatory process. This can be visualized on ultrasound as the increased echogenicity in the periappendiceal fat around an inflamed appendix, correlating with fat-stranding noted on CT. This is very similar to the sonographic changes noted in the soft tissue with cutaneous abscesses.

Common Variants and Selected Abnormalities

An appendicolith, when seen with an enlarged inflamed appendix, helps make the diagnosis of appendicitis. Like renal calculi or gallstones, an appendicoltith appears as a brightly echogenic structure producing dense, anechoic shadowing. Differentiate this echogenicity from air within the lumen, which may produce a “dirty” shadowing artifact of mixed echogenicity (Figure 20-42). The finding of an appendicolith on CT has been shown to have a sensitivity of 65% and specificity of 86% for the diagnosis of appendicitis.140 However, patients with just an isolated finding of an appendicolith without an enlarged appendix or periappendiceal inflammation are at low risk of developing appendicitis.141

A ruptured appendix may be difficult to identify by ultrasound.142,143 It may be surrounded by anechoic fluid or a developing abscess, which may be the only abnormal findings. A pericecal abscess usually demonstrates anechoic fluid with bright, hyperechoic debris (Figure 20-43). The appearance often varies, and the abscess may be loculated and more complex.

Pitfalls

1. Normal appendix. The most important variant is that the diameter of a normal appendix may overlap with what is considered abnormal, so that an appendiceal diameter <6 mm is better at ruling out appendicitis.144 It has been suggested that increasing the normal measurements to 7 mm, or including an outer wall thickness measurement >1.7 mm would increase ultrasound's diagnostic accuracy by decreasing false-positive studies based on size alone.145

2. Visualization of the appendix is heavily dependent on the examiner, and visualization rates are variable. In his original research, Puylaert never identified a normal appendix.89 One study reported that only 2% of normal appendices were seen on ultrasound,62 while another was able to identify a normal appendix in 67% of healthy controls.108 A study looking at healthy controls found a visualization rate of 82%,146 and a study using experienced GI radiologists and advanced techniques reported a visualization rate of 99% in a group of 675 patients.

3. Visualization of proximal portions of the appendix without evaluation to the tip may miss cases with isolated distal inflammation. Furthermore, visualization in a single plane may mistake regional lymph nodes or compressed small bowel for an appendix (Figure 20-44).

4. Sonography has a much lower sensitivity for recognizing appendicitis once perforation has occurred.142,147,148 Peritonitis associated with perforation may inhibit adequate compression, and necrosis of the appendix may render it difficult to visualize.142

5. Air and adipose tissue scatter sound waves and make the ultrasound image difficult or impossible to interpret. In an obese child, a 5.0 MHz transducer may be required to improve tissue penetration. An ultrasound examination may be complicated by an overlying gas-filled bowel or a location that is difficult to visualize, such as the retrocecal region. Positioning the transducer along the flank or even posteriorly may improve visualization of the retrocecal appendix, as does using a free hand positioned behind the patient lifting upward while the anteriorly placed transducer compresses downward.149,238

Case Studies

Case 1

Patient Presentation

A 5-year-old boy presented with a 2-day history of vomiting and diarrhea. The pediatrician told the family over the phone the day prior to start Pedialyte and come to the ED if he did not tolerate oral fluids. On presentation, he appeared uncomfortable and had abdominal distention on examination. There was no identifiable point of maximal tenderness, but he was visibly uncomfortable during the entire exam. He vomited during attempts at oral hydration.

Management Course

IV fluids were started and laboratory tests were drawn. After morphine sulfate was given for pain control, a focused emergency ultrasound exam of the right lower quadrant was performed. Free fluid and diffusely dilated bowel loops were noted on graded compression examination, but the appendix could not be visualized. The psoas muscle and iliac vessels were also difficult to visualize. The radiology department repeated the ultrasound exam. This exam noted the free fluid and measured the appendix at 6 mm, but the tip was not definitively identified and acute appendicitis could not be ruled out. At the request of the surgical consultant, a CT with oral and IV contrast was performed. The CT revealed a ruptured appendix and the patient was transported to the operating room.

Commentary

This case demonstrates both the difficulty of definitive visualization of the appendix by ultrasound and the high frequency of perforation in young children with acute appendicitis. Complete visualization necessitates localizing the blind end of the appendix, which may be the only site of inflammation. If clinical suspicion remains high after an equivocal sonographic exam, further imaging should be considered with consultation from a surgeon. Nonvisualization of the appendix on ultrasound should only be considered a negative study when done by an experienced clinician in a patient with a low probability of disease. In these select cases, the patient may be admitted for observation or discharged with instructions to return for a repeat imaging test if clinical conditions worsen.

Case 2

Patient Presentation

A 12-year-old girl presented to the ED with abdominal pain that localized to the right lower quadrant. The pain began on the previous day as a constant vague pain around the umbilicus. She was unable to eat and had vomited twice prior to arrival. She started menstruating 2 years ago and her last menstrual period was 3 weeks ago. She was found to be afebrile and examination revealed a soft abdomen with tenderness in the right lower quadrant and pain on passive extension of the right leg.

Management Course

An IV line was established with fluids and morphine sulfate administered. Blood was drawn and sent to the laboratory for analysis. Surgery was consulted. A focused examination of the right lower quadrant revealed a tubular, blind-ended, noncompressible structure in the right lower quadrant, arising from the cecum. Midway along its course a brightly echogenic structure with dense shadowing was noted, distal to this the appendix dilated to an outer wall to outer wall diameter of 9 mm. Free fluid and an echogenic inflammatory reaction were noted around the appendix (Figure 20-42). The WBC count was 10,000 cell/μL; however, the surgeon agreed with the diagnosis of acute appendicitis based on the physical examination and ultrasound findings. A nonperforated appendix was removed laparoscopically. Intraoperative and pathology findings confirmed the diagnosis of acute appendicitis.

Commentary

Abdominal pain in the adolescent female may be difficult to diagnose. Ovarian torsion, ectopic pregnancy, pelvic inflammatory disease, and tubo-ovarian abscess are potential diagnoses. In this case, a focused ultrasound examination showed definitive findings of appendicitis, which expedited appropriate surgical management. Overreliance on the WBC count can cause diagnostic errors.

Hypertrophic pyloric stenosis (HPS) is the most common cause of intestinal obstruction and the most common surgical cause of vomiting in infants. Overgrowth of the muscle around the pyloric channel causes a progressive gastric outlet obstruction. It is seen in 3:1000 live births, and males, (particularly first born males), are affected 5 times more often than females.150

HPS is a pathologic hypertrophy of the gastric pylorus muscle that occurs for unknown reasons. The disorder has been associated with elevated gastrin levels as well as dysfunction of the pyloric ganglion cells.151,173 Exposure to erythromycin has been associated with the development of HPS.152 It does not appear to be a congenital disease.153 The hypertrophied muscle obstructs outflow from the stomach, leading to persistent projectile vomiting. While the typical age range of presentation is between 3 and 6 weeks, HPS has been reported as early as 10 days of age and as late as 20 weeks of age.

In 1912, Ramstedt performed the first successful pyloromyotomy, which, a century later, continues as the standard surgical treatment. Pyloromyotomy is curative and long-term sequelae are rare.154,155 Atropine has been successfully used in Japan to reverse pyloric stenosis nonoperatively, but this treatment requires a prolonged hospital stay and a course of oral medication as an outpatient and is not standard of care in the United States.156,157 Left untreated, HPS is typically fatal, as infants continue to vomit and become severely dehydrated with a hypochloremic, hypokalemic metabolic alkalosis.158,173

Clinical Considerations

Classically, the diagnosis of HPS was made in the appropriate age group by palpation of an olive-sized mass in the right upper quadrant in combination with the history of vomiting and metabolic derangement.154,159,160 The number of patients presenting with these classic findings has declined over the last few decades, although it is unclear whether easier and earlier ultrasound access or increased physician awareness is the cause.161–163

Ultrasound has become the standard for diagnosing HPS. It remains an operator dependent examination, but one with an accuracy near 100%.164,165 In cases where the ultrasound examination is nondiagnostic or negative but the patient's signs and symptoms persist, it may be appropriate for the ultrasound to be followed by an upper GI series. Sensitivity by this approach is 100%.159 Another approach is to repeat the ultrasound if the initial study is nondiagnostic or symptoms persist. This approach has a sensitivity of 97%.166

Despite the potential benefits of an upper GI series as the initial diagnostic study, ultrasound predominates as the study of choice for suspected HPS.167,168 Ultrasound is a rapid and noninvasive means of assessing for a hypertrophic pyloric segment using measurements of the pyloric width and length. Unlike an upper GI series, which only implies a hypertrophied muscle by visualization of a thinned channel of barium through the pylorus, the ultrasound examination visualizes the hypertrophied muscle itself. Infants are excellent candidates for ultrasound imaging because of their small size and limited body fat, which allows for the use of a high-frequency transducer producing high-resolution images. Pyloric sonography has been shown to be accurate by both pediatric surgery residents and emergency medicine physicians in several small studies and case series.169–172

Clinical Indications

An ultrasound examination of HPS is indicated in any patient aged 10 days to 20 weeks who presents with nonbilious projectile vomiting. Patients may have a palpable olive-sized mass in the right upper quadrant or visible peristaltic stomach waves. The hypertrophic pylorus may be found during palpation by locating the inferior border of the liver in the right upper quadrant, following it to the mid-epigastrium, then moving the hand caudally while pressing against the vertebral column. The olive-sized mass should roll under the finger tips.173 However, most patients in this era present without long-standing symptoms, and have a normal physical examination.

Anatomical Considerations

The pylorus is contiguous with the stomach and usually lies just to the right of the midline and just caudal to the gallbladder. In cases when the stomach is distended with fluid, the pylorus may become displaced posteriorly, sometimes appearing to curve beneath the stomach and toward the left (Figure 20-45).

Getting Started

The examination is well tolerated and can be done at the bedside with the parent holding the infant, if necessary. Using warm gel and allowing the child to use a pacifier dipped in glucose–water solution may decrease the infant's fussiness during exam. Attempts at breast, formula, or rehydration solution feeding may be deferred until determining if fluid distention is already present in the stomach.

Technique and Normal Ultrasound Findings

The ultrasound examination of HPS consists of identifying the pyloric wall and measuring the muscle wall thickness (MWT) as well as observing the dynamic function of the pylorus over 5–10 minutes.151 The normal pylorus is a ring of muscle separating the pyloric antrum from the duodenum, with a MWT of <3 mm and a length <14 mm.174 As the pyloric muscle pathologically hypertrophies, it both lengthens and thickens.

Perform the examination with a high-frequency linear array transducer in a transverse plane from an anterior approach on the supine patient (Figure 20-46). Using the liver as an acoustic window, begin in a subxiphoid position and trace the anterior gastric wall laterally. Identify the beginning of the pyloric antrum by the incisura angularis, which appears as a notch in the gastric wall. The pyloric muscle, viewed in long axis, will have a slightly thickened appearance, even in the normal patient. The end of the pyloric channel where it meets the first portion of the duodenum is identified by the sudden change in the thickness of the muscle wall, or curved appearance of the pyloric ring (Figure 20-47). The shape and length of the channel changes with peristalsis and may appear differently during different times of the examination. Gastric contents may be seen passing through a dilated channel or air may be present, obscuring views of the posterior pyloric wall. In cases of pylorospasm, the pyloric channel appears collapsed, but should distend again within 5–10 minutes.

Only measure the hypoechoic muscle layer and not the more echogenic mucosa. Measure only on a perpendicular cross section of the pylorus in the midline on a longitudinal section. A changing MWT between 2 and 3 mm with obvious passage of gastric contents into the duodenum indicates a normal pylorus in pylorospasm and not HPS.

Common and Emergent Abnormalities

The pyloric MWT remains the most widely accepted diagnostic standard with high accuracy.168,175 A pyloric MWT >3 mm that does not vary over time is considered diagnostic for HPS (Figure 20-48). In addition, a functional assessment may support or refute the diagnosis of HPS.158,176 In HPS, gastric contents will not be visualized moving through a distensible pylorus. Another finding with HPS includes the “antral nipple sign,” noted when opposed gastric mucosa within the thickened pyloric cylinder project back into the fluid-filled antrum (Figure 20-49).

Common Variants and Other Abnormalities

The most important normal variant to exclude is pylorospasm. The MWT in pylorospasm may exceed 3 mm transiently, but observed over time the muscle wall relaxes and allows passage of gastric contents. Fluid in the colon or small bowel may appear to represent the stomach, leading to the presumption that a portion of the bowel is the pylorus.

Gastric air may obscure visualization of the pylorus. Positioning an infant in a right lateral decubitus position allows gastric fluid to preferentially fill the pyloric antrum creating a better window, while gastric air moves away toward the fundus. In the child with gastric fluid overdistention and a posteriorly positioned pylorus, placing the infant in a left posterior oblique position may elevate the pylorus into a more anterior position closer to the transducer.

Pitfalls

1. The difference between normal and abnormal may be 1 mm or less, so accurate measurement is key. In one study, seven of eight false-negative examinations were due to inaccurate measurements from poor technique.166 Measure only the hypoechoic muscle layer, not the hyperechoic mucosa. Measure only on a perpendicular cross section of the pylorus or in the midline on a longitudinal section.

2. Bilious vomiting suggests obstruction more distally than the pylorus. Consider malrotation with volvulus in such cases.

3. Observe a pylorus with a borderline increased MWT for 5–10 minutes to ensure that the MWT does not vary into the normal range, indicating pylorospasm and not HPS.

4. The esophagus, duodenum, or gastric walls may be mistaken for the pylorus if they are thickened or inflamed. The esophagus may be mistaken for the pylorus, but can be correctly identified by its deep position near the aorta.

Case Study

Patient Presentation

A 20-day-old female infant presented to the ED with 7 days of intermittent vomiting, described as projectile by her mother. Her mother was concerned that she was not producing enough breast milk, so she was supplementing breast-feeding with bottle feeds. The child was vomiting with the bottle feeds and appeared constantly hungry.

On physical examination, the child's vital signs included a blood pressure of 75/50 mm Hg, heart rate 160 beats per minute, respiratory rate 36 per minute, and temperature 37.0°C rectally. The infant was alert and active with a normal physical examination.

Management Course

An emergency ultrasound examination revealed a thickened, elongated pylorus, with gastric peristalsis noted, but no fluid was observed passing through the channel. Surgery was consulted and a confirmatory ultrasound by radiology revealed a thickened elongated pylorus. IV fluids were started. The patient underwent surgical correction the following morning with an uneventful course.

Commentary

This case demonstrates the often-confusing history of vomiting offered by a caregiver. It is estimated that up to 75% of ultrasound examinations for HPS will be negative, which highlights the low accuracy of clinical suspicion for this disease.177

Intussusception is the most common cause of intestinal obstruction in children between 3 months and 6 years of age, with a peak incidence at 10–14 months and 65% of patients presenting under 1 year of age.178 It occurs in about 50 per 100,000 children per year and is more common in the Caucasian population.179,180

The etiology in most cases of intussusception is unknown. It occurs when one piece of bowel invaginates and telescopes into a more distal segment, causing intermittent pain whenever the bowel peristalses on itself. The inciting event is sometimes an anatomical mass or “lead point,” such as a Meckel's diverticulum or a lymphoma that is pushed into the distal segment of bowel by peristalsis. A lead point can be identified in only about 20% of cases of intussusception in children. It is hypothesized that because a common site of intussusception in children is the ileocecal junction, where lymphoid hyperplasia in Peyer's patches may serve as a lead point.181

Patients classically present with a history of severe, intermittent, abdominal pain and intervening periods of lethargy. Although up to 75% of patients have some blood in the stool, the classic triad of intermittent abdominal pain, vomiting, and “currant jelly” stools occurs in <20% of cases.178,182,183 Also, only about half of pediatric patients with intussusception have a palpable abdominal mass, usually in the right upper quadrant. A large prospective study showed that patients have a very low risk of intussusception if they are younger than 5 months of age and have a negative abdominal radiograph, or if they are older than 5 months of age and have a negative radiograph, no bilious vomiting, and the presence of diarrhea.184

Delays in diagnosis lead to increasing bowel wall edema, ischemia, and bowel perforation, and make the need for surgical intervention more likely.185 During the 19th century, intussusception was usually a fatal disorder, but with current diagnostic and treatment tools mortality has been reduced to <1%. If diagnosed early, intussusception can be easily treated with hydrostatic or pneumatic enema reduction under fluoroscopic or ultrasound guidance.186 Short-term recurrence rates of intussusception are between 5% and 10%. Surgical intervention is indicated in cases of suspected bowel ischemia, perforation, or clinical instability.187

Clinical Considerations

The clinical examination has poor specificity, and diagnostic imaging is often necessary.184,188–191 The imaging modalities commonly used in the evaluation of intussusception include plain abdominal radiographs, contrast enemas, and ultrasound.

Typical plain radiograph findings include a “target” or “crescent” shaped soft tissue mass in the right side of the abdomen, lack of cecal gas, or a small bowel obstructive pattern.183,192,193 Plain radiograph specificity is poor, with one study only having 3% of images read as positive as opposed to probable or negative.184 While normal radiographs in combination with low risk history and exam findings may be reassuring, a normal radiograph may miss intussusception in up to 45% of patients.194,195 Obtaining three radiographic views may significantly increase the sensitivity of plain radiographs.188 Plain films are especially helpful if free air is detected since liquid contrast studies are contraindicated in the case of bowel perforation and surgical exploration is mandatory. Unfortunately, free air is not usually seen on plain radiographs of children with intussusception and proven perforation.181

The gold standard for the diagnosis of intussusception has been a contrast enema using barium or air. A contrast enema is both diagnostic and therapeutic. Reduction in the intussusception involves infusing fluid or air rectally, under fluoroscopic or ultrasound guidance, and pushing the telescoped segment out of the bowel into which it is invaginated. Despite being mildly invasive, enema studies are relatively safe, with minimal radiation exposure and a risk of perforation <1%.182

The use of air enemas is currently favored over barium or other liquid enemas due to the increased reported success rates; however, its use is institution dependent.187,196 Air enemas are less messy and require less radiation. They have a slightly higher perforation rate than barium enemas (1.4% vs. 0.2%), but the perforations associated with air enemas are smaller. Leakage of air into the peritoneal space also causes fewer problems than barium leakage.192 When enemas are not initially successful, they may be repeated up to 3 times in selected cases.197–199

Ultrasound has recently gained favor over enema studies as the initial diagnostic study for suspected intussusception. It has the distinct advantage of being entirely noninvasive, requiring no radiation exposure, and can be performed at the bedside if needed.

Multiple studies have demonstrated ultrasound to be 100% accurate in the diagnosis of intussusception (Pracros 1987).154,182,183,192,200,246 Despite the operator variability with ultrasound, one study showed equal accuracy of the sonographic examination between staff radiologists and junior radiology residents.201 In addition, an ultrasound examination can locate pathologic lead points responsible for the intussusception, whereas contrast enemas usually cannot. Ultrasound can also identify signs that may predict failure in enema reduction, such as trapped free fluid,202,203 intramural air,204 or absence of blood flow on Doppler imaging.205–207 None of these findings are contraindications to attempting an enema reduction in a stable patient.

The major disadvantage of ultrasound is that if intussusception is diagnosed, the patient still requires a contrast enema for reduction. Ultrasound guidance has been used with enema reduction with success rates comparable to fluoroscopy.186,208,243

Some controversy remains as to whether an ultrasound examination or a contrast enema study should be the initial imaging modality for intussusception.209

Clinical Indications

An ultrasound examination is indicated in any patient suspected of having intussusception. These patients usually present with severe, intermittent abdominal pain, often associated with vomiting, a right upper quadrant mass, or guaiac-positive stool.

Anatomical Considerations

The most common type of intussusception in the typical age range (6 months to 2 years) is an ileocolic intussusception. The cecum is located in the right lower quadrant and is the gas-filled structure sandwiched between the anterior abdominal musculature and the large posterior psoas muscle. Telescoping of terminal ileum into the cecum gives rise to the classically described mass. In 45% of cases of intussusception in children age 5 years or younger, the sigmoid colon loops into the right lower quadrant, and should not be confused with the cecum.181

Technique and Normal Ultrasound Findings

Use a high-frequency linear array transducer to assess for intussusception. Scan the child in the supine position. Use warmed conducting gel if available.

Begin the examination in the transverse plane at the hepatic flexure, identifying the transverse and ascending colon. From there, the ascending colon can be traced down the lateral abdomen toward the cecum in the right lower quadrant. Identifying the actively peristalsing terminal ileum transitioning into a normal cecum rules out an ileocolic intussusception.

The normal colon is differentiated from small bowel by its larger size and aperistalsis. Large bowel will also have regular haustral markings, best seen on the ascending colon in sagittal view in the right abdomen (Figure 20-50). Normal bowel may contain air (bright echoes with shadowing artifact just under the anterior wall or mixed with fecal matter), fluid (anchoic), or stool (mixed or speckled echogenicity).

If an abdominal mass can be palpated by physical exam, this area should be imaged in multiple planes. If no mass is palpated and a normal ileocecal junction is not appreciated in the right lower quadrant (added), then the path of colon should be followed from the cecum and terminal ileum to as far distally as possible, looking for a mass just deep to the abdominal wall.

Common and Emergent Abnormalities

An ileocolic intussusception is most commonly found in the right upper quadrant.243 When imaged along its longitudinal plane, the segment of intussuscepted bowel may appear to have multiple thick hypoechoic layers that are distinctly different from normal proximal and distal bowel, or may have the general appearance of a kidney (“pseudokidney sign”) (Figure 20-51A).

Another well-described finding is of a sonodense center (bowel contents) surrounded by a sonolucent ring (bowel wall), which is known as the “target sign.” This is seen on transverse views of the bowel (Figure 20-51B). The typical intussusception is 3–5 cm in diameter, which will nearly fill the image on the ultrasound display making it relatively easy to identify.181

Common Variants and Other Abnormalities

Another diagnosis is made in up to 20% of cases of suspected intussusception. In a quarter of these cases, the ultrasound examination will find alternate abnormalities, including nonspecific bowel wall thickening (Crohn's disease, Henoch–Schönlein purpura, or enterocolitis), dilated loops of bowel filled with fluid, free intra-abdominal fluid, enlarged mesenteric lymph nodes, ovarian cysts, or volvulus. Free intraperitoneal fluid does not necessarily imply perforation and may be seen in up to 50% of patients with intussusception.210,211

In 5% of pediatric intussusception cases, a lead point exists and may be seen on an ultrasound examination.212 Meckel's diverticula, duplication cysts, polyps, or lymphoma may serve as lead points. An ultrasound examination may identify other masses, such as a polycystic kidney or Wilm's tumor, or identify complications such as pneumoperitoneum.

Pitfalls

False-positive ultrasound examinations are usually due to clinician inexperience. In one study, the most common imitator of intussusception was fecal matter in the colon.200 Other reported false-positive findings include hematoma of the bowel wall associated with Henoch–Schönlein purpura and nonspecific bowel wall edema or inflammation.200

Case Study

Patient Presentation

A healthy 2-year-old boy was brought to the ED by his parents after experiencing 24 hours of severe intermittent abdominal pain. The parents reported that the episodes lasted for a few minutes and then subsided. He had vomited twice. On physical examination, his vital signs were normal. He appeared tired, but in no distress. The patient's abdomen was soft and nontender on examination. Rectal examination revealed guaiac-positive stool.

Management Course

An initial plain radiograph showed a nonobstructive bowel gas pattern, but with no bowel gas noted in the right lower quadrant. An emergency ultrasound examination demonstrated a mass in the RUQ with typical multilayered hypoechoic rings consistent with intussusception (Figure 20-52). Reduction by air enema was successful.

Commentary

This case demonstrates the appropriate use of emergency ultrasound in suspected intussusception. The patient was stable with a normal physical exam. A plain radiograph was nondiagnostic. Normal single view radiographs should be interpreted with caution in a patient with suspected intussusception. The choice to proceed to emergency ultrasound versus contrast enema depends on the level of suspicion. In patients with a classic history of colicky pain, vomiting and bloody stool, with a mass palpated in the right abdomen on exam providers may decide to start with a contrast enema. In patients with equivocal findings, it may be best to limit radiation exposure, avoid discomfort, and save time by starting with an ultrasound examination.

An accurate clinical determination of hydration status has historically been difficult to obtain in pediatric patients presenting to the ED with suspected dehydration. The gold standard measure of dehydration is change in body weight over the course of illness, which is often not available in the acute setting. Historical information such as oral intake and stool and urine output is often imprecise. Alternative methods of assessment, which rely on a constellation of signs, symptoms, and laboratory values, often prove subjective and inaccurate as well.213,214

Clinical Considerations

Significant dehydration, which is defined as a deficit of 5% or more of body weight, can be identified objectively by comparing the maximum diameter of the IVC to the aorta. This rapid and noninvasive method has been found to be relatively accurate.215 A comparison of IVC/aorta ratio to the World Health Organization dehydration scale and to IVC inspiratory collapse showed that IVC/aorta ratio performed better in correctly determining severe dehydration in children.216 In addition, this simple application allows physicians with varying levels of ultrasound training to reliably obtain comparable measurements of hydration status.216

Determining the IVC/aorta ratio can help clinicians identify patients with significant dehydration who may otherwise go unrecognized. This application may also reduce unnecessary interventions and the use of medical resources by identifying patients who can be safely treated with oral rehydration therapy alone. This is especially important in resource-limited settings.216

Clinical Indications

Ultrasound determination of hydration status is indicated in pediatric patients who may have significant dehydration. A similar technique may also be used to determine hypovolemic shock in pediatric patients.

Anatomical Considerations

The IVC and aorta are both visible in the transverse plane just anterior to the vertebral bodies in the upper abdomen. The IVC appears as a nonpulsatile structure posterior to the liver, located to the right of the pulsatile aorta. The shape of the IVC ranges from circular to oval to flat depending on the patient's hydration status. The IVC normally collapses with inspiration.

Getting Started

The IVC/aorta ratio can be accurately measured with the patient in the supine position, either on the bed or on the caregiver's lap, which may decrease anxiety and facilitate image acquisition. Warmed gel may also be beneficial in keeping patients comfortable and calm throughout the examination.

Technique and Normal Ultrasound Findings

A high-frequency linear array or microconvex transducer is best for neonates and infants, and a phased-array transducer is best for larger children and adolescents. Adjustments to depth, frequency, and gain may further improve image quality and the accuracy of the measurements.

To acquire a transverse image of the IVC and aorta, place the transducer in the subxiphoid region in the midline. Obtain measurements of the anterior–posterior diameter of both vessels by freezing the image and scrolling back through the cine loop to apply the calipers (Figure 20-53). Measure the maximal width of the IVC (in the expiratory phase of the respiratory cycle) and the maximal width of the aorta (in systole).217

Alternatively, scan the vessels in the longitudinal plane. Identifying the IVC in the longitudinal plane may be more challenging in dehydrated patients, but it allows the operator to visualize the specific location of the IVC measurement. The IVC is most commonly measured about 2–3 cm caudal to the hepatic vein inlet (Figure 20-54), and it should not be measured at the junction of the right atrium.218

Common Abnormalities

An IVC/aorta ratio of ≤0.8 suggests significant dehydration. This cutoff yields a sensitivity of 86–93% and a specificity of 56–59%.215,216

Common Variants and Other Abnormalities

An IVC/aorta ratio of 1.2 or greater, and no collapse of the IVC with inspiration or sniffing, suggests fluid overload (also see Chapter 6, “Cardiac”).219

Pitfalls

1. Ultrasound evaluation of hydration status using the IVC/aorta ratio can only determine the current hydration status of the patient. The prognostic value of this measurement and its role in guiding rehydration therapy are unknown.

2. Care must be taken when measuring the anterior–posterior diameter of both the IVC and aorta in the longitudinal view. The transducer must be parallel and centered above the vessel to assure that the true diameter is measured. For this reason, measurements in the transverse plane may be more accurate.

3. Measure the IVC caudal to the hepatic vein inlet and cephalad to the renal vein. Measurements at the junction of the right atrium and IVC may be erroneous due to the attachment of the muscular diaphragm, which decreases vessel compliance.218 Transitioning from a longitudinal view, in which the hepatic vein is well visualized, to a transverse view for measurement may be the best approach.

4. The accuracy of the IVC/aorta ratio is dependent on normal cardiac function and normal pulmonary pressures. Decreased cardiac function or increased pulmonary pressures can alter the caliber of the IVC and cause an overestimation of hydration status.

5. A reversal of IVC respiratory changes occur in mechanically ventilated patients and the IVC distends during insufflation. Significant distention during insufflation (>18%) is a predictor of fluid responsiveness (see Chapter 8, “Critical Care,” and Chapter 6, “Cardiac”).

Case Study

Patient Presentation

A 2-year-old male child presented with a 5-day history of severe diarrhea. The stool was nonbloody and watery, and required a diaper change every 30 minutes. He was tolerating minimal fluids by mouth and did not produce urine for 8 hours. He was afebrile. His blood pressure was 90/60 mm Hg, heart rate 118 beats per minute, respiratory rate 28 per minute, and oxygen saturation 98% on room air. On physical exam, the patient had low-energy, mucous membranes were dry, and his eyes appeared sunken. Capillary refill was 3 seconds. There was diaper dermatitis on his buttocks. The diaper was clean and dry.

Management Course

Oral rehydration therapy was initiated at triage and well tolerated. Emergency ultrasound showed an IVC/aorta ratio of 1.0. The patient was discharged on oral therapy and made a full recovery without further medical intervention.

Commentary

This case demonstrates the benefits of using emergency ultrasound as a diagnostic tool in determining hydration status in patients at risk of significant dehydration. An accurate noninvasive measure can be achieved rapidly.

Clinical Considerations

Urine collection for the purpose of urinalysis and culture is a common procedure in pediatric patients who are unable to voluntarily provide a urine sample. The current preferred method for collecting urine is urethral catheterization due to its minimally invasive nature. Nursing staff typically performs this safe, accurate, and rapid procedure at the bedside.220

An equally effective alternative to urine catheterization is bladder aspiration. This technique is typically reserved for patients in whom a urethral catheterization cannot be performed due to an anatomical barrier or is contraindicated due to urethral pathology. Suprapubic aspiration may also be necessary for bladder drainage in the setting of traumatic urethral injury or urinary retention.

Complication rates with either procedure are reported at the very low rate of 0.2%.221 The most common complication of urethral catheterization is microhematuria, which resolves spontaneously. Other complications such as cystitis are rare. The most common complication of suprapubic aspiration is also microhematuria, which occurs in up to 4% of cases and typically resolves within 24 hours.222 Other complications such as bowel perforation and gross hematuria seldom occur and often resolve without further sequelae.223,224

The use of ultrasound improves the success rates of both techniques.59 Urethral catheterization success rises from 70% to 95% with the addition of ultrasound 225,226. Ultrasound also increases suprapubic aspiration success rates from about 60% to as high as 96%.222,226,227

Clinical Indications

An ultrasound-assisted urethral catheterization or ultrasound-guided suprapubic aspiration is indicated for pediatric patients who are unable to voluntarily void and need an uncontaminated urine specimen and for patients who have urinary retention or obstruction. The clinical scenario will dictate which procedure is appropriate.

Anatomical Considerations

The bladder is located in the midline of the lower abdomen and is posterior to the symphysis pubis when empty. It expands spherically above the symphysis pubis when filled with urine. In younger infants the bladder enlarges posteriorly as it fills (as opposed to cephalad), which may make suprapubic aspiration more challenging. The bladder is anterior to the peritoneal space and, when full or partially full, is the first abdominal structure encountered when passing from anterior to posterior at a level just above the symphysis pubis. This relationship makes it possible to insert a needle into the bladder from the anterior abdomen without placing any of the other abdominal organs at risk of puncture.

Getting Started

Identification of the bladder and assessment of bladder volume can be achieved with the patient in nearly any position. Perform ultrasound-guided bladder aspiration with the patient in the supine position. Patients undergoing aspiration may benefit from age-appropriate restraints and the use of noninvasive anxiolytic adjuncts or medications.

Technique and Normal Ultrasound Findings

Use a linear array, microconvex, or phased-array transducer to scan the bladder depending on the size of the patient. Place the transducer in a sagittal orientation just above the symphysis pubis in the midline of the lower abdomen (Figure 20-55). The transducer is correctly placed if caudal movement of the transducer causes the symphysis pubis to shadow most of the screen. Identify the bladder in the midline as a triangular-shaped cystic structure. The corners appear more rounded when the bladder is full.

Urethral Catheterization

Use ultrasound to assist with urethral catheterization by viewing the bladder just prior to the procedure. This ensures that there is sufficient urine in the bladder so that an unsuccessful (“dry”) catheterization can be avoided. Ultrasound is especially helpful if an empty bladder is likely due to recent voiding or significant dehydration.

Several methods have been described for estimating adequacy of bladder volume for urine collection, which is defined as a minimum 2.5 mL of urine. One-dimensional, two-dimensional, and three-dimensional measurement techniques result in approximately the same success rates, ranging from 94% to 100%.225,228,229 Sample sizes in these studies are too low to show any real differences between techniques. The simplest technique is to measure the transverse bladder diameter and postpone catheterization until the diameter is ≥2 cm (Figure 20-56).228 Rehydration therapy for 30 minutes is usually sufficient to adequately fill the bladder.

Suprapubic Aspiration

Ultrasound can be used in two distinct fashions when performing a suprapubic aspiration. Ultrasound-assisted means that ultrasound is used primarily to determine whether sufficient urine exists in the bladder to perform a successful suprapubic aspiration, and secondarily to confirm the best location to insert the needle; however, ultrasound is not used during the needle insertion. Ultrasound-guided implies continuous real-time visualization of the needle during placement. For the initial attempt at the procedure, there appears to be no significant advantage of choosing ultrasound-guided over an ultrasound-assisted suprapubic aspiration in terms of success rate.226

Sufficient volume must be present prior to an attempt at needle aspiration. Successful urine collection is expected if the transverse diameter measurement exceeds 3.5 cm, while failure is likely if the measurement is <3.0 cm.230 If the bladder diameter is inadequate, it can be rechecked in about 30 minutes.

Prior to needle insertion, scan the bladder in the transverse plane to confirm midline position. After using sterile precautions, insert a 22- or 23-gauge needle of adequate length directly over the bladder and perpendicularly to the skin, one fingerbreadth above the symphysis pubis (Figure 20-57). Maintain constant negative pressure on the syringe while the needle is advanced toward the bladder. Advance the needle until it enters the bladder and urine fills the syringe. Determine the maximal depth of needle placement by the depth markers on the ultrasound image. If no urine is returned after a single ultrasound-assisted attempt, then use real-time ultrasound-guidance for the second attempt.

Pitfalls

1. Infants may spontaneously void if startled by cold ultrasound gel or pressure on their bladder. For this reason, warmed gel and minimal transducer pressure are preferred.220

2. Suprapubic aspiration has the potential for serious iatrogenic injury, although complications are exceedingly rare.

3. Other fluid-filled structures may be misidentified as the bladder. Thorough visualization of the bladder and surrounding anatomy will decrease this risk. The characteristic walls of the bladder help differentiate it from free intra-abdominal fluid that tracks around adjacent structures. Fluid-filled bowel will have intermittent peristalsis and heterogenous content.

Case Study

Patient Presentation

A 14-month-old baby girl presented with 5 days of fever. She had been vomiting and unable to tolerate fluids for the past 2 days. She had no urine output for 6 hours prior to arrival. On physical examination, her initial blood pressure was 70/40 mm Hg, heart rate 160 beats per minute, respiratory rate 50 per minute, rectal temperature 38.6°C, and an oxygen saturation of 100% on room air. The patient was tender to palpation in the suprapubic region of the abdomen. She was alert, mucous membranes were dry, and her eyes were sunken. Capillary refill was 2 seconds.

Management Course

IV access was established and IV fluids were started. Point-of-care ultrasound revealed an empty bladder. A repeat ultrasound exam after 30 minutes of IV rehydration showed a partially filled bladder with a transverse diameter measurement of 3.8 cm. A successful urethral catheterization was then performed. Urinalysis confirmed a urinary tract infection and antibiotic therapy was initiated.

Commentary

This case demonstrates the advantage of ultrasound assistance in performing a successful urethral catheterization. An unsuccessful (“dry”) urethral catheterization was avoided.

The authors acknowledge the contributions of Daniel Price and Michael Peterson, who authored this chapter in the second edition.