Despite the advent of cross-sectional radiographic imaging and high-definition ultrasonography and a more than doubling of their use in recent years, detection rates for appendicitis have essentially remained the same.16 There are numerous appendicitis mimics, and the differential diagnosis is broad (Table 81-1). Perform a complete physical examination, including a pelvic examination in women of childbearing age. Acute appendicitis is largely a clinical diagnosis, and no one adjunctive test is universally indicated.
TABLE 81-1Differential Diagnosis of Right Lower Quadrant Pain ||Download (.pdf) TABLE 81-1 Differential Diagnosis of Right Lower Quadrant Pain
Crohn's/ulcerative colitis flair
Functional abdominal pain
Incarcerated inguinal hernia
Ovarian vein thrombosis
Referred testicular pain
Abdominal wall/rectus sheath hematoma
Consider appendicitis in any patient with atraumatic right-sided abdominal, periumbilical, or flank pain who has not previously undergone appendectomy. Available diagnostic adjuncts include peripheral WBC and other acute inflammatory markers (e.g., C-reactive protein or erythrocyte sedimentation rate), urinalysis, and a pregnancy test. Diagnostic imaging should be considered in atypical presentations or if significant diagnostic uncertainty exists after thorough history and examination.
Scoring systems, such as the Alvarado and Samuel scores, have been developed to aid in diagnosis. The modified Alvarado score for acute appendicitis ranks symptoms (migration, 1 point; anorexia or urinary acetone, 1 point; nausea or vomiting, 1 point), signs (right lower quadrant tenderness, 2 points; rebound, 1 point; fever, 1 point), and WBC count (>10,000/mm3, 2 points) into low-risk appendicitis (score, 1 to 4) and possible or probable appendicitis (score, 5 to 9). However, the low-risk score (score, 1 to 4) was demonstrated as only 72% sensitive compared to 93% for clinical judgment when appendicitis was either the most likely or second most likely diagnosis.17 Despite continued technologic advances and development of decision rules, different scoring systems often yield conflicting results and should not replace clinical judgment; the clinical impression of the experienced physician has the highest impact on patient outcome.18,19,20,21
An increase in peripheral WBC may be the earliest marker of inflammation.22 A study of 722 children identified both prospectively and retrospectively found acute appendicitis to be the most common diagnosis in children >4 years old with nontraumatic abdominal pain and leukocytosis.23 However, a normal WBC is not uncommon, and leukopenic presentations have been documented.24 While numerous studies have evaluated the use of the WBC, there is no clear consensus on its utility.22,23,25,26,27 The WBC does not distinguish between simple and perforated appendicitis.25 C-reactive protein and the erythrocyte sedimentation rate used alone lack the sensitivity and specificity to rule in or rule out the diagnosis. If the only diagnostic consideration is acute appendicitis (yes or no), the greatest utility of laboratory tests may be in combination: an elevated WBC and/or C-reactive protein may have a combined sensitivity as high as 98%. Normal values of both in patients with a low pretest probability of acute appendicitis make pathologically confirmed appendicitis very unlikely.27,28,29,30,31 However, WBC and C-reactive protein levels are elevated in a number of other appendicitis mimics, so these markers are not useful if the differential diagnosis of pain is broad.32,33
Obtain a urinalysis because isolated microscopic hematuria may support a diagnosis of renal colic, and pyuria may suggest pyelonephritis. However, hematuria or sterile pyuria can be present in acute appendicitis.11 Document a negative pregnancy test in females of reproductive age to rule out ectopic or heterotopic pregnancy. Other laboratory tests are not routinely indicated but may be beneficial when considering other diagnoses.
Obtain early surgical consultation before imaging in straightforward cases of suspected appendicitis in adults. Imaging is not universally necessary but may be of benefit in certain populations.34,35,36 In children, some centers prefer pediatric surgery consultation prior to imaging with ionizing radiation.
When adjunctive imaging is indicated, early surgical consultation may aid guidance in imaging selection. The goal of imaging is to establish the diagnosis of appendicitis, avoid a negative appendectomy, identify perforation, and exclude other causes of abdominal pain with minimal radiation, cost, and time.
Plain radiography is not helpful. Findings are typically nonspecific but may demonstrate a nonspecific bowel gas pattern or adynamic ileus. An appendicolith may be visualized in up to 50% of children with appendicitis.35
Graded compression US should be the initial imaging modality of choice in both pregnant females37 and children. It can likewise be considered in young, nonobese adults. Reports of the effectiveness of US diagnosis of appendicitis in pregnancy are conflicting, with some reporting US as useful38 and others reporting it as ineffective for diagnosis.39 Regardless, US is safe, fast, well tolerated, and cost-effective.
The appendix is oval in the axial plane, ends blindly in the longitudinal plane, and should be compressible with a maximal diameter not exceeding 6 mm.40 The normal appendix is typically differentiated from small bowel on US by the absence of peristalsis and the lack of change in configuration over time; its small size distinguishes it from large bowel. Typical findings in appendicitis are a thickened, noncompressible appendix >6 mm in diameter (Figure 81-1). Doppler US may illustrate hyperemia.35 It is important to image the entire length of the appendix, because inflammation may be more pronounced at or localized to the distal end.40 Given the highly operator-dependent nature of US, centers treating larger volumes of children may have greater reproducibility of high-quality studies. The diagnostic accuracy of abdominal US in children is better at ruling in acute appendicitis than excluding it.41 Besides operator skill, other limitations to accuracy include cases of retrocecal appendicitis or perforation, excessive abdominal guarding or bowel gas, a gravid uterus or obese habitus, a decompressed bladder, and lack of patient cooperation. Perforation may lead to disappearance of specific imaging hallmarks and difficult visualization of the appendix on US. Pelvic US may be useful in cases of suspected appendicitis and a nondiagnostic abdominal US or CT,42 or in the differentiation of appendicitis from pelvic inflammatory disease43 (see chapter 97, "Abdominal and Pelvic Pain in the Nonpregnant Female").
Ultrasonographic demonstration of acute appendicitis. A noncompressible, inflamed appendix (red circles) is shown in a cross-sectional view (A; 7.5 MHz) and a longitudinal section (B; 7.5 MHz). Mural lamination of the swollen appendix is maintained in the early stages of acute appendicitis. C. An appendicolith (arrow) with acoustic shadowing is demonstrated (5 MHz). [Reprinted with permission from Ma OJ, Mateer JR, Reardon RF, Blaivas M. Emergency Ultrasound. 3rd ed. Copyright © The McGraw-Hill Companies, 2014, All rights reserved. Chapter 11, General Surgery Applications, Figures 11-31A&B & 11-33.]
In most adult males and nonpregnant females for whom the diagnosis of appendicitis is not sufficiently clear, consider abdominal CT that includes the abdomen and pelvis. Typical CT findings include a dilated appendix >6 mm with a thickened wall, periappendiceal inflammation, and potential visualization of an appendicolith or abscess.44 Luminal obstruction and dilation may be relieved in cases of perforation, leading to disappearance of specific imaging hallmarks and difficult visualization of the appendix on CT.11
The accepted sensitivity of CT (composite studies using oral or IV contrast or no contrast) for the diagnosis of acute appendicitis is typically >94%, with a positive predictive value >95% (Figure 81-2).34,36 In a comparison of CT versus US, the overall sensitivity of CT in patients >2 years old was 96%, with a 96% positive predictive value; graded compression US had an overall sensitivity of 86%, with a 95% positive predictive value.36 In this same study,36 women who had preoperative imaging had a statistically significant lower negative appendectomy rate than women who had no imaging, suggesting that women with suspected acute appendicitis derive the greatest benefit from preoperative imaging. Appendiceal CT, a less frequently used protocol, uses rectally administered contrast only with acquisition of thin cuts through the right iliac fossa. This avoids the difficulties of oral contrast administration in patients with active emesis and prevents potential adverse reactions of IV contrast. Time to acquisition of images is much shorter, typically around 15 minutes after administration of rectal contrast, but may produce significant patient discomfort.45,46
Acute appendicitis on contrast CT scan as evidenced by dilated and inflamed appendix (red circle).
Oral and IV Contrast versus Nonenhanced CT Oral contrast medium has historically been recommended for CT of the abdomen and pelvis when investigating a broad differential of GI or pelvic diagnoses, and many centers continue to recommend CT imaging with both IV and oral contrast. Yet, a growing body of literature calls this practice into question. Multiple studies indicate that nonenhanced CT has excellent performance in the diagnosis of acute appendicitis.47,48,49,50,51,52,53 The imaging evaluation of abdominal pain is time intensive and impacts ED overcrowding. Unenhanced studies can significantly decrease the time to diagnosis and eliminate patient discomfort from oral (especially in vomiting patients) or rectal contrast, and avoids altogether the risk of renal injury from IV contrast. More than 52% of 462 patients who underwent CT imaging in at least one study had no oral, IV, or rectal contrast administered, with a combined sensitivity of 93% and a positive predictive value greater than 92%, supporting the suitability of nonenhanced CT imaging for making the diagnosis.36 A comparison of nonenhanced CT with findings on laparoscopy reported 95% sensitivity with 100% specificity of nonenhanced CT in suspected appendicitis,2 whereas another systematic review reported a pooled sensitivity of 92.7% (95% CI, 89.5% to 95.0%) and specificity of 96.1% (95% CI, 94.2% to 97.5%).47 Another systematic review of 23 studies showed equivalent or improved diagnostic performance of nonenhanced CT when compared to oral contrast.36 Oral contrast frequently does not reach the terminal ileum at the time of imaging, yet in this group of patients, at least one author has shown no diagnostic compromise in the performance of imaging.52 Several studies attribute disagreement between nonenhanced CT and contrasted studies more to interobserver variability than contrast medium.51,53 Noncontrast CT should be considered an accepTable imaging modality in the workup of acute appendicitis. In patients with renal insufficiency or dye allergy, administration of IV contrast is contraindicated. Body habitus may limit reproduction of noncontrast CT test characteristics; intraperitoneal fat serves as an intrinsic contrast medium in unenhanced CT, and its paucity in very thin patients can affect imaging interpretation.44,45,54
Consider MRI as another reliable imaging technology in the evaluation of acute appendicitis, particularly in pregnant women. MRI avoids ionizing radiation and visualizes the entire abdomen in multiple planes. In a survey of U.S. academic medical centers with radiology residency programs, MRI was preferred over CT (39% vs. 32%) for evaluation of appendicitis in the first trimester of pregnancy. This preference reversed in the second and third trimesters.37 IV gadolinium crosses the placenta and is not used in pregnancy given the teratogenic effects seen in animal studies.55 Gadolinium is not given to patients with renal insufficiency because it may cause nephrogenic fibrosing dermopathy. Avoid MRI in the evaluation of the unsTable patient given the time necessary for study acquisition. Sedation may be required for small children, rendering it impractical in many pediatric cases.