Chapter 50: Appendicitis

• Appendicitis is the most common surgical illness of childhood.

• The presentation of appendicitis in children is variable, and many other conditions mimic it, such as right lower lobe pneumonia, mesenteric adenitis, and gastroenteritis.

• Blood tests such as white blood cell count, CRP, and procalcitonin can be helpful, but are not reliable for excluding appendicitis.

• Diagnostic imaging is not required in children with obvious appendicitis.

• Ultrasound is the initial imaging modality of choice with computed tomography reserved for nondefinitive sonographic studies.

• Clinical decision rules that identify low risk for appendicitis should be used to avoid clinical investigations in these children.

Appendicitis is the commonest surgical emergency in children and its prompt identification is often challenging. Meticulous history and physical examination supported by the judicious use of diagnostic imaging are the mainstays of its diagnosis.

Lifetime appendicitis risk is approximately 8% with males slightly higher than females. Under the age of 3 years, perforation rates are close to 100%, likely secondary to delays in presentation, and missed diagnosis secondary to overlap of symptoms with more common ailments such as gastroenteritis. In adolescence, perforation rates decrease to approximately 15%. Appendicitis is more common in the early summer when enteric infections are high as well.¹

The infant's appendix is somewhat funnel-shaped and becomes tubular after the age of 2 years.¹ Appendicitis begins with luminal obstruction by an appendicolith, foreign body, parasite, or lymphoid follicle hyperplasia. This leads to continued inflammation, mucous production, and eventual perforation resulting in peritonitis or abscess formation. Perforation rates range between 25% and 40%.

Missed appendicitis is one of the most frequent reasons for litigation in pediatrics. Appendicitis is missed upon first presentation approximately 28% of the time. Gastroenteritis, constipation, and urinary tract infections are common diagnoses in those patients with a misdiagnosis.¹

The history is a crucial part of the evaluation of acute appendicitis, and particular features of the history will vary with age. The diagnosis is particularly challenging in children less than 3 years old because preverbal children cannot provide history, and the clinical course is often more rapid and frequently atypical compared with older children. Young children will more often have vomiting and irritability as their primary presentation, which has significant overlap with other diagnoses. Abdominal pain is not easy to elicit from a history, and if so, the patients are less likely to have focal right lower quadrant pain than older children. Because they frequently have perforated appendicitis at diagnosis, they have higher temperatures and higher rates of bilious emesis and bowel obstruction.

As children become more verbal, and the anatomy of the appendix changes, the historical features tend to become more reliable. The classic presentation of periumbilical pain, nausea, and migration of pain to the right lower quadrant is less frequent in children and is only reported in about one-third of patients. As opposed to adults, children are more likely to present with vomiting first, then followed by abdominal pain. Diarrhea is a frequent complaint and should not be assumed to indicate gastroenteritis. Older children often report anorexia, and pain with walking, coughing, or jumping.

Referred pain to the abdomen mimicking appendicitis is also common, and asking about respiratory and genitourinary symptoms is important. A classic example is a right lower lobe pneumonia that refers pain to the abdomen mimicking appendicitis.¹

Low-grade fever is often present early in the course of appendicitis but its absence does not rule it out. Tachycardia is a nonspecific finding noted in most children presenting with pain or fever. It is important to evaluate the child's perfusion and respiratory status assessing for evidence of compensated or decompensated shock. The classic findings of right lower quadrant tenderness, vomiting, and fever are less frequent in children than adults; especially in younger children. Evaluation of gait is a nonthreatening way to assess for peritoneal irritation. If they are in pain, they may walk hunched over, or may be unable to walk at all. Younger children with significant stranger anxiety can be very difficult to examine. It is best, if possible, to examine these children in the arms of the caregiver, and one should pay special attention at this age to abdominal findings such as irritability with palpation, firmness, or distension. As children grow older and become verbal, the utility of bedside tests of peritoneal irritation (Table 50-1) becomes more useful. Pain with coughing, jumping, or walking can be elicited during the course of examination and its presence increases the likelihood of appendicitis.

Chest and pulmonary examination may reveal lower-lobe crackles suggesting pneumonia. The genitalia should be examined. Testicular torsion and hernias can present with referred pain to the abdomen mimicking appendicitis. The rectal examination is of low utility and is best avoided.¹

A suggestive history and consistent physical examination is often enough evidence to proceed directly to surgery without further testing. This decision is surgeon- and institution-dependent. A multidisciplinary care guideline can often minimize variation, and recent evidence shows decrease in ancillary testing in settings where these guidelines exist.²

Clinicians frequently order lab tests in children with suspected appendicitis. Urine should be tested for infection but the presence of pyuria does not exclude the diagnosis of appendicitis. The white blood cell (WBC) count is typically obtained, but it is nonspecific and insensitive for appendicitis. Its sensitivity increases with longer duration of symptoms and with perforation. Some decision rules, however, have found that a normal to low WBC count does help stratify a population of children who are at low risk of acute appendicitis.^3,4

Diagnostic Imaging

Radiography is rarely helpful in the diagnosis of appendicitis unless an appendicolith is seen. Many surgeons will proceed directly to surgery without further imaging if the remainder of the presentation is consistent.

Ultrasound (Fig. 50-1), despite lower sensitivity and specificity than computed tomography (CT) for appendicitis, is the initial diagnostic imaging modality of choice because of concern regarding radiation exposure.⁵ Pooled estimates of sensitivity and specificity have been reported to be 88% and 94%, respectively.⁶ However, more recent reports do not show such high sensitivities. The ability to identify the appendix on ultrasound improved with time, and sensitivities were as low as 61% when done “after hours.” Sensitivity varies with the duration of symptoms with it being lower early on (∼80%) and rising to near 100% as the disease progresses.⁷ Thus, both operator experience and timing of symptoms play a role in the utility of ultrasound. Children early in the course of disease should have strategies that rely on observation, serial examination, repeat ultrasounds, or CT scans if indicated. If the ultrasound is not definitive, then a CT should be done.

CT (Fig. 50-2) has sensitivity and specificity in the mid- to high 90s.^6–8 The choice of contrast for these CTs varies according to institution-specific guidelines, but has not been shown to impact the test characteristics significantly.⁹ One must consult with their local radiologists to ensure that the ionizing radiation levels used are the lowest needed for adequate images. MRI is now being studied, and ultrafast MRI without sedation is promising as another radiation-sparing imaging modality.¹⁰

Scoring Systems and Clinical Decision Rules

In recent years, the development and attempted validation of pediatric appendicitis scoring systems and clinical prediction rules have increased. The most frequently used scoring systems are the Alvarado score and the Samuel score.^11,12 Preliminary data from the development cohorts were promising, but subsequent validation studies have shown mixed results.^13–18 There is utility at the extremes of scores. These are scores of children in whom the presence or absence of appendicitis is not difficult. Not surprisingly, these scoring systems are less reliable in clinically challenging patients.

Clinical prediction rules have been developed but attempts at validation have been challenging. Kharbanda et al. have described the following prospectively validated prediction rule: an absolute neutrophil count of 6.75 × 10³/μL or less and no maximal tenderness in the right lower quadrant, or an absolute neutrophil count of 6.75 × 10³/μL or less with maximal tenderness in the right lower quadrant but no abdominal pain with walking, jumping, or coughing. This refined rule had a sensitivity of 98.1%, specificity of 23.7%, and negative predictive value of 95.3%.⁴

No scoring system or clinical prediction rule can completely exclude or completely make the diagnosis of appendicitis without a small percentage of children undergoing a negative appendectomy. The data do, however, provide the practitioner some strategies to avoid immediate imaging, especially CT scan, and observe a subset of patients that are at low risk.

Management includes fluid resuscitation, pain control, and antibiotic administration. Tachycardia, delayed capillary refill, and other signs of decreased end-organ perfusion such as altered mental status and poor urine output mandate immediate IV fluid resuscitation. Patients who present with vomiting, poor oral intake, or history of decreased urine output should have IV fluids started. Patients will also be expected to be NPO during the evaluation, and maintaining adequate intravascular blood volume is essential.

Pain control has been controversial with concerns that it may mask the diagnosis of appendicitis. However, allowing patients with suspected appendicitis to suffer pain is not acceptable. Recent literature supports that the provision of opioid analgesia does not mask the diagnosis of appendicitis.^19,20 Four randomized clinical trials in children demonstrated the expected efficacy of opioids for reducing pain but were not significantly powered to address the question of decreased diagnostic precision.¹⁹ However, the rates of missed appendicitis, perforations, appendectomies, appendectomies with a normal appendix, and children with appendicitis being observed prior to appendectomy were virtually the same whether or not an opioid was administered.²⁰ This strongly supports no deleterious effect upon diagnostic precision. Pain control with adequate doses of morphine or fentanyl should be given after the emergency physician has assessed the patient and is awaiting surgical consultation. Good communication with the surgical team and a clinical care pathway can be helpful in expediting care in these patients.

Preoperative antibiotic administration in cases of nonruptured appendicitis has been debated. Most studies suggest that postoperative infectious complications are lower in those treated with preoperative antibiotics. Preoperative antibiotic therapy for suspected ruptured appendicitis is less controversial. Many regimens are used with the choice often being institution's preference. A systematic review by the American Pediatric Surgical Association recommends ceftriaxone and metronidazole as the most cost-effective combination.²¹