Pediatric Appendicitis Workup

Making a timely diagnosis of appendicitis is a difficult challenge in children with abdominal pain. Laboratory findings may increase suspicion of appendicitis but are not diagnostic. The minimum laboratory workup for a patient with possible appendicitis includes a white blood cell (WBC) count with differential and urinalysis. Liver function tests and amylase and lipase assessments are helpful when the etiology is unclear.

Other studies, such as interleukin 6 and C-reactive protein (CRP) assays, have been advocated by some in the diagnosis of appendicitis. However, in multiple clinical series, these studies have not been shown to be of clear benefit and, for the most part, only add to the cost of the evaluation.

The WBC count becomes elevated in approximately 70-90% of patients with acute appendicitis. However, the WBC count is elevated in many other abdominal conditions, as well. Furthermore, the WBC count is often within the reference range within the first 24 hours of symptoms. Elevation tends to occur only as the disease process progresses, and it is usually mild. Therefore, its predictive value is limited. Elevation of the neutrophil or band count can be seen without elevation of the total WBC count and may support the diagnosis of appendicitis.

If the WBCs exceed 15,000 cells/μL, the patient is more likely to have a perforation. However, one study found no difference in the WBC counts of children with simple appendicitis and those with perforated appendicitis. In the immunocompromised patient, a neutrophil count of less than 800 may suggest typhlitis.

Urinalysis is useful for detecting urinary tract disease, including infection and renal stones. However, irritation of the bladder or ureter by an inflamed appendix may result in a few urinary WBCs. The presence of 20 or more WBCs per high-power field (hpf) suggests a urinary tract infection.

Hematuria may be caused by renal stones, urinary tract infection, Henoch-Schönlein purpura, or hemolytic-uremic syndrome. However, small numbers of red blood cells (RBCs) can be found in as many as 20% of patients with appendicitis when an overlying phlegmon or abscess lies adjacent to the ureter. Typically, urinary RBCs are fewer than 20/hpf.

Normal urinalysis results have no diagnostic value for appendicitis. However, a grossly abnormal result may suggest an alternative cause of abdominal pain

Abdominal radiography findings are normal in many individuals with appendicitis. However, plain films may be helpful in the setting of severe constipation. A calcified appendiceal fecalith is present in less than 10% of persons with inflammation, but its presence suggests the diagnosis.

Radiographic signs suggestive of appendicitis include convex lumbar scoliosis, obliteration of the right psoas margin, right lower quadrant (RLQ) air-fluid levels, air in the appendix, and localized ileus. In rare incidents, a perforated appendix may produce pneumoperitoneum.

If no other imaging studies are to be performed, an abdominal series is strongly suggested.

For more information, see the Medscape Reference article Appendicitis Imaging.

Given the potential risks of radiation from CT scans, graded compression ultrasonography may be the preferred initial imaging modality in the evaluation of pediatric acute appendicitis. This technique involves locating the appendix and then attempting to compress its lumen.

For ultrasonography to be diagnostic of appendicitis, the operator must visualize the appendix. Even if the appendix is not visualized, however, appendicitis can be excluded more confidently if ultrasonography shows no secondary signs of appendicitis (eg, hyperechoic mesenteric fat, fluid collection, localized dilated small bowel loop).^[4]

A positive finding is a noncompressible tubular structure 6 mm or wider in the RLQ (see the images below). This structure is tender during palpation with the ultrasonographic probe. Additional supportive findings include an appendicolith, fluid in the appendiceal lumen, focal tenderness over the inflamed appendix (sonographic McBurney point), and a transverse diameter of 6 mm or larger. In patients with a perforated appendix, ultrasonography may reveal a periappendiceal phlegmon or abscess formation.

Abdominal ultrasonography has proved to be valuable for diagnosing appendicitis in children, with most published reports indicating a sensitivity, specificity, and accuracy of at least 90-95%. Furthermore, some authors have found that ultrasonography is more sensitive and specific than clinical impression and increases diagnostic accuracy when used either alone or in conjunction with laboratory results.^[5]

The advantages of ultrasonography include its noninvasiveness, lack of radiation, no contrast medium, and minimal pain. The downside of ultrasonography is that the examination is operator dependent and may not be available at some institutions. Factors that add difficulty to the examination include obesity and gaseous distention of the intestines overlying the appendix. However, results of one study determined that ultrasonography should continue to be the first diagnostic imaging study in suspected appendicitis, regardless of the child's body mass index (BMI).^[6]

Ultrasonography is also useful in diagnosing alternative pathologies (eg, tubo-ovarian abscess, ovarian torsion, ovarian cyst, mesenteric adenitis).

A prospective study by Lowe et al comparing noncontrast CT scanning and ultrasonography revealed a sensitivity, specificity, and accuracy of 97%, 100%, and 98%, respectively, for unenhanced CT scanning, compared to 100%, 88%, and 91%, respectively, for ultrasonography.^[7] Still others have shown that the perforation rate and negative appendectomy rate can be decreased by using both tests in tandem.

For more information, see the Medscape Reference article Appendicitis Imaging.

CT scanning is a useful modality for diagnosing appendicitis in children. Although radiation exposure is a concern, CT scans have been shown to have an accuracy of 97% in diagnosing appendicitis. Advantages of CT scan include the availability at most institutions, the ability to evaluate the entire abdomen and locate abscesses and phlegmon, the lack of dependence on operator skill, and physician familiarity with reading CT scans.

CT findings that are indicative of appendicitis include a thickened appendix, fat streaking around the appendix, or thickening of the cecal wall (see the images below).

CT findings that suggest perforated appendicitis include periappendiceal or pericecal air, abscess, phlegmon, and extensive free fluid. Because the disease is due to obstruction of the appendix and the inflammation occurs distal to the obstruction, extravasation of contrast or extensive free air is rarely seen. If a patient is found to have free air throughout the abdomen or under the diaphragm, other diagnoses should be entertained.

CT scanning may be helpful in obese patients or those in whom a localized appendiceal abscess is clinically suspected. In patients with abscesses, CT scanning may also be helpful in the CT-guided drainage of the abscess.

CT scanning has been found to have sensitivity, specificity, and accuracy similar to those of ultrasonography.^{[7, 8]} Disadvantages include the aforementioned radiation exposure, the need for oral and intravenous contrast and its related disadvantages, and the need for the patient to be still, which is often difficult for small children.

Because of the advantages of CT scans, 62% of surveyed North American pediatric surgeons preferred it for evaluation of appendicitis. Of note, less than 1% of pediatric surgeons favored CT scanning for every case of suspected appendicitis. Most preferred CT scanning on a selected basis, with 51-58% of patients with suspected appendicitis undergoing CT scanning.

However, despite now-widespread use of CT scanning for evaluation of appendicitis with its superior sensitivity and specificity, the negative appendectomy rate in children has not shown a statistically significant reduction.

Peck et al and Mullins et al have reported sensitivities of 92-97% and sensitivities of 99.6-99%, respectively, using noncontrast helical CT scanning.^{[8, 9]} Callahan et al reported equivalent results using helical CT scanning and rectally administered contrast material.^[10] They reported that this technique results in decreased total number of inpatient observation days, decreased number of negative laparotomies, and decreased per-patient cost.

Additional radiographic testing is clearly indicated in patients who present with equivocal signs and symptoms of appendicitis. Whether noncontrast CT scanning, rectally administered contrast-enhanced CT scanning, CT scanning with oral and intravenous contrast, or ultrasonography is used may be a function of the institution or time of day. The data clearly show that each has sensitivities and specificities over 90% and that each can be helpful in clinical decision-making.

For more information, see Appendicitis Imaging.

If the history, physical examination, laboratory tests, and imaging studies have failed to produce a satisfactory differential diagnosis, anteroposterior (AP) and lateral chest radiography should be performed to look for right lower lobe pneumonia.

Typically, histologic findings range from acute inflammatory infiltrate most apparent in the submucosal level in early appendicitis to transmural infarction in perforated appendicitis.

The finding of an apparently normal appendix at surgery requires careful follow-up of the histologic findings. Occasionally, early appendicitis is histologically identified and clinically correlates with the resolution of preoperative symptoms. Additionally, unsuspected findings of luminal nematodes should indicate further anthelmintic therapy (eg, mebendazole [Vermox]). Chronic inflammation or fibrosis of the tip of the appendix are occasionally seen and coincide with resolution of the symptoms.

Many surgeons now encounter patients with “early appendicitis” based on history, physical examination findings, and/or CT scans who had minimal changes found in the appendix in the operating room or only intraluminal inflammatory cells on histology. Most of these patients have complete resolution of their signs and symptoms after appendectomy. Whether this is because the appendectomy is performed at an earlier stage of appendicitis or is due to the placebo effect of the appendectomy is unknown.

For more information, see the Medscape Reference article Appendicitis Imaging.

Electrolyte assessments and renal function tests are more helpful for management than diagnosis. Indications for these tests include a significant history of vomiting or clinical suspicion of significant dehydration.

A beta–human chorionic gonadotropin (beta-HCG) test should be performed to rule out pregnancy or ectopic pregnancy in adolescent girls.

Evaluation rules and algorithms have been proposed to help the clinician make the correct diagnosis and treatment plan. Although these decision rules may help predict which children are at low risk for appendicitis, they are not used consistently

Kharbanda et al scoring system

The system proposed by Kharbanda et al assigns scores based on the following 6 findings^[11] :

• Nausea (2 points)
• History of focal RLQ pain (2 points)
• Migration of pain (1 point)
• Difficulty walking (1 point)
• Rebound tenderness/pain with percussion (2 points)
• Absolute neutrophil count of greater than 6.75 X 10³/µL (6 points)

A score of 5 or less had a sensitivity of 96.3%, a negative predictive value of 95.6%, and a negative likelihood ratio of 0.102 in the validation set.

The Samuel score (pediatric appendicitis score)

This scoring system is based on 8 variables, as follows^[12] :

• RLQ tenderness elicited by cough, hopping, or percussion
• Anorexia
• Elevated temperature
• Nausea/vomiting
• Tenderness over the right iliac fossa
• Leukocytosis
• Increased polymorphonuclear neutrophil percentage (ie, left shift on white blood cell differential)
• Migration of pain

Samuel recommended that patients with a score of 5 or lower should be observed, while those with a score of 6 or higher should undergo surgical consultation.

The Alvarado score (MANTRELS score)

The MANTRELS score is based on the following 8 variables:

• Migration of pain to RLQ
• Anorexia
• Nausea/vomiting
• Tenderness in RLQ
• Rebound pain
• Elevated temperature (>37.3° C)
• Leukocytosis (>10,000/µL)
• Left shift

Schneider et al found that an Alvarado score of 7 or higher yielded a sensitivity of 73% and a specificity of 80%.^[13] Use of this scoring system is limited to risk stratification of suspected appendicitis in children.

The clinical staging of appendicitis has important implications in the postoperative treatment of the child. Although somewhat subjective at the time of surgery, appendicitis may be divided into 3 broad categories: acute (nongangrenous), suppurative or gangrenous (nonperforated), and perforated. Perforated appendicitis can be divided further into cases with diffuse or with localized peritonitis.

Acute (nongangrenous) appendicitis

This stage of appendicitis is referred to as early appendicitis. No mural gangrene or infarction is present. This type requires no further antibiotic therapy in most settings. The child may be discharged home as soon as diet and oral pain medications can be tolerated.

Suppurative or gangrenous (nonperforated) appendicitis

Patients with exudative appendicitis, particularly those with mural gangrene, have an increased rate of postoperative intra-abdominal and wound infections, even in the absence of demonstrable perforations. Often, microperforations are present and may be identified if cultures of the fluid are obtained. However, if the the child is clinically improved and Gram stain and culture findings, if available, are negative, the intravenous antibiotics can be stopped in approximately 24 hours, and the child may be discharged home as soon as diet and oral pain medications can be tolerated. A decision can be made by the surgeon to continue oral antibiotics at home.

Perforated appendicitis

Perforated appendicitis (diagnosed either by intraoperative findings or by positive intraoperative cultures) is associated with a postoperative infection rate of as high as 30%. Children with perforated appendicitis require antibiotic therapy for a minimum of 7-10 days. Often, intra-abdominal abscesses that require drainage may develop. A high index of suspicion for a postoperative abscess is required in the patient with perforated appendicitis who has fevers or ileus that last more than 5 days. A child who develops a postoperative abscess or a small bowel obstruction may need additional surgery and may have a prolonged hospital stay.