Chapter 21. Emergency Ultrasound

Clinical Summary

The focused assessment with sonography for trauma (FAST) examination is a safe, portable, noninvasive diagnostic tool to investigate for hemoperitoneum, hemopericardium, and hemothorax in trauma victims. The FAST exam can help detect free fluid (ie, hemoperitoneum in the hypotensive patient); however, the FAST exam cannot exclude solid organ injury. Hemoperitoneum in the pediatric trauma patient is usually a result of hepatic or splenic injury and will appear as an anechoic (dark) collection on ultrasound (US). The primary indications for use of the FAST exam are blunt or penetrating thoracic or abdominal trauma.

Technique

Use a low-frequency (1–5 MHz) curvilinear abdominal or phased-array probe or higher-frequency (6–12 MHz) linear transducers. The latter will provide better resolution as pediatric patients have thinner abdominal walls and less subcutaneous fat. Perform the scan with the patient in the supine position. Direct probe indicator toward the patient’s head or the patient’s right side. When imaging the right upper quadrant (RUQ) and the left upper quadrant (LUQ), rotate the probe counterclockwise during scanning to allow for successful imaging between intercostal rib spaces.

Obtain the following four views:

1. Subxiphoid view of the heart

2. Hepatorenal space (Morison pouch) in the right upper quadrant (RUQ)

3. Splenorenal recess, as well as the subphrenic space, in the left upper quadrant (LUQ)

4. Suprapubic view

   1. Rectovesicular pouch (males)

   2. Pouch of Douglas (females)

   3. RUQ and pelvic views are routinely performed first in the pediatric trauma patient as these are most sensitive in detecting intraperitoneal free fluid

Findings

Free fluid in RUQ appears as an anechoic collection between the liver and the right kidney. This dependent space is the most sensitive view to detect the hemoperitoneum, and it is the most important view. On the LUQ view, blood from a splenic injury appears first above the spleen in the left subphrenic space. If the volume is large enough, blood will collect in the splenorenal space and soon flow to other dependent spaces in the abdomen (ie, hepatorenal space, suprapubic space).

Use suprapubic imaging to visualize the bladder in both transverse and sagittal views. The bladder is a fluid-containing, anechoic structure on US, and serves as an acoustic window to detect free fluid in the dependent space below it. Use the pubic symphysis as an anatomic landmark for probe placement. Obtain a transverse view with the probe indicator directed toward the patient’s right side and a sagittal view with the probe indicator directed toward the patient’s head. Suprapubic imaging also helps to assess bladder volume before the placement of Foley catheters or sterile catheterizations.

Obtain a subxiphoid view to detect pericardial fluid, particularly in penetrating trauma. Direct the probe marker to the patient’s right side with the transducer below the xiphoid process and aim toward the patient’s left shoulder. Pericardial fluid appears as a dark, anechoic stripe between the heart and the liver.

Pearls

1. Obtain a surgical consult immediately in a hypotensive patient (unresponsive to fluid boluses and blood) with a positive FAST exam for expeditious transport to the operating room.

2. Patients with a positive FAST and stable vital signs can be managed conservatively in the pediatric intensive care unit (PICU) with serial blood counts, repeat physical exams, and vital signs.

3. FAST exam does not rule out intra-abdominal solid organ injury; a computed tomographic (CT) scan should strongly be considered in patients with heightened suspicion for injury.

4. A parasternal-long view of the heart can also be used to evaluate for free fluid when images of the heart cannot be obtained from the subxiphoid view.

Clinical Summary

Consider bedside US in patients with signs and symptoms suspicious for appendicitis, particularly when physical examination is unreliable. Ultrasound is a safe, nonionizing method of diagnosing appendicitis in patients with heightened suspicion. Ultrasound has poor sensitivity because it is highly operator dependent but is used to supplement the history and physical examination in patients presenting with possible appendicitis.

Technique

Use a high-frequency (6–12 MHz) linear probe. In patients with a larger body habitus, deeper visualization of the abdomen may be required, necessitating the use of the low-frequency (2–5 MHz) curvilinear [abdominal] probe. Place the patient comfortably in the supine position and direct the probe indicator toward the patient’s head or the patient’s right side. Begin scanning in the RLQ, as lateral as possible, with the probe marker aimed toward the patient’s head and gently advance the probe toward the midline, until the probe approaches the point of maximal tenderness. Use gentle, graded compression to displace gas from the bowel and move the probe closer to the appendix. Measure the diameter of the appendix in both long and short axes, from outer wall to outer wall.

Ultrasound Findings

A normal appendix has a diameter of <6 mm on US and should demonstrate peristalsis, and normally collapse with gentle compression. Ultrasound features supportive of a diagnosis of appendicitis include noncompressibility, diameter of >6 mm (in either plane), lack of peristalsis, and a bull’s-eye appearance when viewed in the transverse (short-axis) plane.

Pearls

1. Do not delay management of suspected appendicitis for US, and obtain a surgical consult immediately.

2. Do not use negative US to rule out appendicitis. If appendicitis is suspected and bedside US is nonconfirmatory, an official radiologist-performed US should be obtained and/or a CT scan should be considered.

3. If an inflamed appendix has perforated, US has a much lower sensitivity in detecting an appendicitis.

4. Finding the iliac vessels adjacent to the psoas muscle in the RLQ is another good starting location to search for the appendix.

Clinical Summary

Bedside US (noninvasive and nonradiating qualities) has become the accepted first-line diagnostic test for patients with suspected intussusception. An experienced sonographer can identify the lead point (ie, lymphoma, polyps, cysts) as well as assess blood flow to affected bowel segments.

Technique

Use a high-frequency (6–12 MHz) linear probe, or in patients with a larger body habitus, a low-frequency (2–5 MHz) curvilinear probe for deeper visualization of the abdomen. Perform the scan with the patient comfortably in the supine position. If an abdominal mass is noted on inspection or palpation, scan the mass in at least 2 planes. If no mass is immediately appreciated, scan the abdomen slowly along the path of the bowel, beginning from the ileocecal region (RLQ), and scan in a clockwise fashion around the abdomen, keeping note for any potential mass(es) below the abdominal wall.

Ultrasound Findings

The normal, unaffected bowel appears as a uniform, thin, hypoechoic rim around an echogenic centrum of variable widths and demonstrates peristaltic activity. An intussuscepted bowel appears as a “target sign,” in the transverse view representing alternating layers of mucosa, muscularis, and serosa or the “sandwich sign,” in the longitudinal view, representing alternating layers of hypoechoic bowel wall.

Pearls

1. Contrast or air enema is required for reduction regardless of how intussusception is diagnosed.

2. Fecal matter in the colon can imitate intussusception on US.

3. Be aware of other pathologic causes of bowel wall thickening that can resemble an intussusception on US (ie, inflammatory bowel disease).

Clinical Summary

Idiopathic hypertrophic pyloric stenosis is the most common surgical diagnosis in an infant, and requires pylorotomy. Pyloric stenosis typically presents in the first month of life with nonbilious vomiting which may become projectile. There may be a characteristic palpable olive-sized mass in the RUQ or peristaltic wave. Ultrasound spares contrast administration and radiation, making it the initial diagnostic study of choice when working up a patient with suspected pyloric stenosis. The sensitivity and specificity of US for the diagnosis of idiopathic hypertrophic pyloric stenosis approaches 100%. Nondiagnostic US is often followed by a fluoroscopic upper gastrointestinal series, which can also exclude other potential gastrointestinal pathologies (ie, malrotation, gastroesophageal reflux).

Technique

Use a high-frequency (6–12 MHz) linear probe as the neonatal stomach and pylorus are relatively superficial anatomic structures. Warm the US gel prior to the exam for patient comfort and perform the scan with the patient in a supine position. Begin the scan in the transverse plane, with the probe indicator directed toward the patient’s right side, in the subxiphoid region. Visualize the stomach first as it is larger and fluid filled (from the obstructing, hypertrophied pylorus), appearing as a large anechoic structure; following the stomach caudally will lead to the pylorus.

Ultrasound Findings

If the stomach is distended, the pylorus may be distorted and/or displaced, making it difficult to visualize. In this case, consider placement of a nasogastric tube to evacuate stomach contents. Gently rolling the patient in the left lateral decubitus position may also facilitate visualization of the pylorus. Once the pylorus is identified, measure the muscle wall thickness in the transverse and longitudinal planes. A transverse measurement of >3 mm or a longitudinal measurement of >17 mm is consistent with pyloric stenosis. Measure the muscle wall thickness of the pylorus muscle in transverse or longitudinal planes. Ensure that the pylorus is visualized for 5 minutes or more to verify that the muscle wall thickness remains consistently thickened. Visualization of the antral nipple sign—the redundant gastric mucosa that protrudes into the antral stomach—is also consistent with the diagnosis.

Pearls

1. Ensure that the plane of measurement is transverse or longitudinal and not oblique to the cross section or long axis of the pylorus.

2. Pylorospasm also results in false positives, which can be avoided by observing the pylorus for at least 5 minutes; a hypertrophied pyloric wall will always remain thickened.

3. Severe dehydration secondary to vomiting and poor oral intake may affect pyloric muscle thickness; adequate fluid resuscitation is indicated in such cases with a high suspicion for pyloric stenosis.

Clinical Summary

Biliary pathology frequently involves adolescents, especially those with sickle cell disease and obese boys. Ultrasound has high sensitivities and specificities for diagnosing gallstones and acute cholecystitis. The “sonographic Murphy sign” is a highly sensitive finding for acute cholecystitis. Ultrasound is indicated in patients with suspected gallstones or acute cholecystitis.

Technique

Use a low-frequency (1–5 MHz) curvilinear or phased array probe or a high-frequency (6–12 MHz) linear probe. Place the patient in a supine position with the head of the bed elevated or in the left lateral decubitus position to help bring the gallbladder into view from the surrounding ribs. Instructing the patient to breathe in deeply or hold their breath may assist in better gallbladder visualization. Scan the gallbladder in both long and short axes, with the probe marker directed toward the patient’s head or right side, respectively. Next, scan the gallbladder from the fundus to the neck checking for stones or pockets of pericholecystic fluid. Pay special attention to a potential sonographic Murphy sign during the exam (elicited by localizing the gallbladder with the US probe and attempting to find the point of maximal pain around the gallbladder). Measure the anterior gallbladder wall (in the near field) from outer wall to outer wall: normal gallbladder wall thickness should be <3 mm. Identify and measure the common bile duct (CBD) and identify the portal triad. Use color or power Doppler to identify the CBD by appreciating the absence of color when compared to the portal vein and hepatic artery, which will demonstrate blood flow.

Ultrasound Findings

Gallstones appear as hyperechoic foci of varying sizes within the anechoic gallbladder, and usually have associated shadows immediately inferior to them as the US beams are reflected back to the transducer. Gallstones lie in the most dependent part of the gallbladder, unless impacted (ie, in the gallbladder neck). Changing the position of the patient will often demonstrate movement of the gallstones. Gallstones may be confused with gallbladder polyps, which are not as hyperechoic as gallstones, immobile, and adhere to the internal segments of the gallbladder wall.

Consider a diagnosis of cholecystitis if: anterior gallbladder wall thickness exceeds 3 mm, there is noted pericholecystic fluid, or a sonographic Murphy sign is elicited. Pericholecystic fluid is not always appreciated with acute cholecystitis but has been found to be specific for the diagnosis.

Pearls

1. Visualize the entire gallbladder from fundus to neck.

2. Gallbladder wall thickness may be caused by a number of pathologic entities (ie, ascites, hepatitis, HIV, pancreatitis) and may not necessarily imply a case of cholecystitis.

3. Measure the anterior (near-field) wall of the gallbladder for near-accurate assessment of gallbladder wall thickness as acoustic enhancement may falsely increase posterior (far-field) wall measurements.

Clinical Summary

Emergency-physician-performed US is established as a safe, rapid, and nonradiating form of diagnostic imaging for managing gynecologic and obstetric complaints and has become the standard of care for patients presenting with abdominal, pelvic pain, and/or vaginal bleeding during the first trimester. Exclusion of ectopic pregnancy during the first trimester by visualization of an intrauterine pregnancy (IUP) is the most common application. In the hemodynamically unstable patient, FAST can allow for visualization of free fluid, allowing rapid identification of patients requiring immediate surgical intervention for suspected ruptured ectopic pregnancy. The differential diagnosis is also assisted by identification of other acute gynecologic pathologies (ie, ovarian torsion, tubo-ovarian abscess, or pelvic mass).

Positioning and Technique

Use a low-frequency (1–5 MHz) curvilinear or phased-array probe for transabdominal imaging and a high-frequency (4–7 MHz) endocavitary probe for transvaginal imaging. With the patient in the supine position, obtain transabdominal imaging in both longitudinal and transverse planes; then with the probe marker toward the head, obtain a longitudinal view of the uterus. Rotate the probe counterclockwise, so that the probe indicator is pointed toward the patient’s right side to obtain a transverse view of the uterus. If pregnancy is early and an IUP cannot be visualized well on abdominal US or if better visualization is desired, proceed to transvaginal imaging and scan completely through the uterus and adnexal regions. Obtain multiple views of the uterus beginning with the longitudinal axis (sagittal plane) looking for the endometrial stripe, and scan the entire length of the uterus from left to right, as well as laterally to visualize the adnexa. Turn the probe counterclockwise with the probe indicator directed to the patient’s right side to visualize the uterus in the transverse plane. Determine whether there is evidence of an IUP (ie, yolk sac or fetal pole) and correlate US findings with quantitative assessment of beta human chorionic gonadotropin (β-hCG) blood levels as follows:

1. With a β-hCG between 1500 to 3000 mIU/mL, a yolk sac should be visualized on transvaginal US.

2. With a β-hCG between 6000 to 6500 mIU/mL, a yolk sac should be visualized on transabdominal US.

If an IUP is appreciated, organized cardiac activity should be sought if a fetal pole is present. Fetal heart movement can be captured using a video clip or by using M-mode US.

Ultrasound Findings

The normal prepubertal uterus has a tubular configuration on US without an apparent endometrium and a length of 3 to 4 cm with a thickness that does not exceed 10 mm. A pubertal uterus has a pear-shaped configuration with average length of 5 to 9 cm and width of 3 to 4 cm. Endometrial lining varies with the menstrual cycle. The normal prepubertal ovary measures 1 cm in length by 1 cm in height by 1 cm in depth on US. A pubertal ovary measures 3 cm in length by 2 cm in height by 2 cm in depth.

Ovarian torsion is more common with a predisposing lesion, such as an ovarian cyst or mass. An 8- to 12-mm mean gestational sac diameter should contain a yolk sac. An 18- to 22-mm mean gestational sac diameter should contain a fetal pole. A 5-mm fetal pole should contain a fetal heartbeat.

Pearls

1. Always attempt to visualize the uterus in 2 planes.

2. A full bladder provides the best acoustic windows for transabdominal visualization of the uterus and adnexa, while an empty bladder yields better evaluation on transvaginal sonography.

3. If a gestational sac is noted, attempt to visualize it in long and short axes.

4. If there is high suspicion for an ectopic pregnancy, examine the hepatorenal space for possible free fluid.

5. An empty uterus with a low β-hCG level should not exclude an ectopic pregnancy as close to half of ectopic pregnancies present with a β-hCG level <1000 mIU/mL.

Clinical Summary

Ultrasound is a safe, nonionizing, and repeatable method of assessing parenchymal or pleural diseases in the dyspneic or critically ill pediatric patient. Ultrasound has better sensitivity than a supine chest x-ray for detecting pneumothorax or pleural fluid, especially in the critically ill patient in which an upright or decubitus chest x-ray cannot be performed. Lung US is a viable alternative to CT or radiographs for evaluation of pediatric pneumonia. Ultrasound can also be used in real time to assess endotracheal tube placement. The lack of lung sliding of the left hemithorax after intubation is indicative of a right main stem intubation.

Positioning and Technique

Use a high-frequency (6–12 MHz) linear array or a high-frequency (5–8 MHz) micro-convex array with the patient in the supine position and the probe indicator pointed toward the patient’s head. Scan in longitudinal (sagittal) and coronal planes, moving through all rib spaces of the anterior, axillary, and posterior chest wall.

Ultrasound Findings

The pleural space is found between and slightly inferior to the ribs, and a strong acoustic interface between the pleura and aerated lung produces strong posterior reverberations. This allows for visualization of normal pleural sliding motion of the lung during respiration. In pneumothorax, no lung sliding is seen. When there is fluid in the pleural space (eg, pneumonia, pulmonary edema, pulmonary contusion, or acute respiratory distress syndrome), strong reverberation artifacts generate comet-tail artifacts running the entire length of the image. When normal aerated lung becomes consolidated or atelectatic, it becomes possible to examine the lung parenchyma with US. Airless, consolidated lung appears sonographically similar to the liver (oftentimes described as “hepatization”), making it possible to visualize air bronchograms as branching linear echogenicities. The sonographic appearance of pleural fluid depends on its composition. The fluid may be completely anechoic from a transudative process, to more echogenic from an infectious process or hemorrhage, to having internal septations from an empyema or an organized infection.

Pearls

1. Lung US is based on the visualization and interpretation of artifacts.

2. Scan all lung fields on both hemithoraces.

3. A “lung point”—the interface between sliding and nonsliding lung—is pathognomonic for a pneumothorax.

4. Bedside US is sensitive to determine rib fractures.

Clinical Summary

Cellulitis (see also Chapter 7) can be appreciated on bedside US in most cases by identifying the accumulation of associated edematous fluid. Ultrasound can aid in identifying the extent of the cellulitis surrounding an abscess and is helpful in addressing the extent of the abscess, presence of fluid, and the best location for incision and drainage (I&D) by identifying the “pocket” and any surrounding structures (ie, artery) that must be avoided during I&D.

Positioning and Technique

Because the skin and subcutaneous tissues are relatively superficial, the high-frequency (6–12 MHz) linear probe is often employed, affording higher-resolution images. In patients with a larger body habitus, deeper visualization of the tissue may be required, necessitating the use of the low-frequency (2–5 MHz) curvilinear probe. Place the patient in a comfortable position depending on the location of the cellulitis and/or abscess with the affected area readily exposed. Use gentle manipulation and pressure of the US transducer as the affected area may be sensitive and painful, and warm the US gel medium to room temperature for patient comfort.

Ultrasound Findings

Compare affected tissue with normal skin and subcutaneous tissue to appreciate subtle findings. Cellulitis exhibits hyperechoic skin, and a reticulated pattern of areas of hypoechoic edema, which can be seen with the probe in either longitudinal or transverse axes, with depth and gain adjustments. The lacelike appearance of the edematous tissue has been described as cobble-stoning. Abscesses appear as hypoechoic fluid collections, spherical or irregular in shape, and often surrounded by edematous soft tissue. The (purulent) abscess cavity may contain debris or septations, which can appear as hyperechoic regions in the anechoic collection on US. Use color flow Doppler to differentiate abscesses (no color) from vascular structures (colored). Necrotizing fasciitis can also be visualized on US, with hyperechoic artifacts generating dirty shadowing.

Pearls

1. Identify any adjacent structures (ie, nerve, artery, or vein) that can potentially be injured before I&D of an abscess.

2. Ultrasound should not supplement a good physical exam for the diagnosis of necrotizing fasciitis.

Clinical Summary

Consider bedside US for children presenting with hip pain, a painful limp, or refusal to bear weight to identify hip effusion(s) or perform US-guided hip arthrocentesis.

Positioning and Technique

Use a high-frequency (7–12 MHz) linear array transducer and place the patient comfortably in the supine position with legs in neutral position. Scan with the US transducer in a sagittal-oblique plane, parallel to the long axis of the femoral head.

Ultrasound Findings

A capsular-synovial thickness >5 mm measured at the concavity of the femoral-synovial neck, from the anterior surface of the femoral neck to the posterior surface of the iliopsoas muscle, or a >2-mm difference compared to the asymptomatic contralateral hip is suggestive of hip effusion.

A septic hip may show increased echogenicity, a thick articular capsule (>2 mm), and/or increased capsular blood flow on power Doppler.

Pearls

1. Ultrasound alone cannot make the distinction between infected and inflammatory effusions.

2. Real-time US-guided arthrocentesis can increase success rate of the aspiration of hip effusions.

Clinical Summary

Ultrasound is a rapid, nonionizing tool for evaluating pediatric factures and evaluating the success of a fracture reduction, especially the forearm. The reflective acoustic properties of cortical bone make US highly specific for fractures as small as 1 mm.

Positioning and Technique

Use a high-frequency (7–12 MHz) linear array transducer and a low-frequency (2–5 MHz) curvilinear transducer for deeper structures (ie, femur). Scan the bone(s) of interest in both the longitudinal (parallel) and transverse (perpendicular) planes. Note that only the near-field cortex of bone will be identified.

Ultrasound Findings

Cortical bone is hyperechoic on US due to its strong acoustic impedance, and disruption or loss of the normal contour of the near-field cortical bone is strongly suggestive for fracture. The posterior fossa of the elbow can be identified by applying the US beam in parallel with the posterior distal humerus following the triceps insertion on the olecranon.

Pearls

1. Do not confuse growth plates with fractures.

2. If the posterior fat pad of the distal humerus is elevated on US, there is a fracture about the elbow.