Between 250,000 and 300,000 appendectomies for acute appendicitis are performed each year in the United States,¹ with an additional 700,000 patients affected in the European community.² The lifetime risk of acute appendicitis in the United States is an estimated 12% for males and 25% for females.³ Yet, the epidemiology of this common ED diagnosis continues to change. Data suggest a reversal of a previous decline in incidence, with the annual rate increasing from 7.62 to 9.38 per 10,000 between 1993 and 2008,⁴ whereas the rate of negative appendectomy has declined.⁵ Similarly, between 2001 and 2008 the rate of perforation decreased, but this declining trend has not been consistent.^4,6 Acute appendicitis is most common in patients aged 10 to 19 years,⁴ remains the most frequent cause of atraumatic abdominal pain in children >1 year old,⁷ and is the most common nonobstetric surgical emergency in pregnancy, complicating up to 1 in 1500 pregnancies.^8,9 Despite advances in lab testing and imaging, accurate diagnosis is a challenge. Both “missed appendicitis” and unnecessary surgery for a false diagnosis are not without consequence. Thus, consider appendicitis in any patient with acute atraumatic abdominal pain without prior appendectomy.

Appendicitis is caused by luminal obstruction of the vermiform appendix, typically by a fecalith. Other less frequent causes include obstruction by lymphatic tissue, gallstone, tumor, or parasites. Continued secretion from the luminal mucosa results in increased intraluminal pressure and appendiceal vascular insufficiency, leading ultimately to bacterial proliferation and inflammation. Left unchecked, perforation may occur.

Visceral innervation produces the vague, hard to localize periumbilical or central abdominal discomfort frequently observed early in the clinical course. Progressive inflammation and subsequent irritation of the somatically innervated parietal peritoneum produces the classic migration of pain to the right lower quadrant, to McBurney’s point, located one third of the distance from the anterior superior iliac spine to the umbilicus. Up to 50% of patients may have an atypical presentation¹⁰ due in part to anatomic variation. For example, a retrocecal appendix produces right flank or pelvic pain, whereas malrotation of the colon results in transposition of the appendix and, subsequently, pain to the left upper quadrant. Abdominal organ displacement from a gravid uterus may lead to right upper quadrant tenderness in pregnancy. Even so, a right lower quadrant location of pain remains the most common location of pain in pregnant women with appendicitis.⁹

The signs and symptoms of acute appendicitis lie along a spectrum that correlates with pathophysiology. Early on, patients classically complain of nonspecific symptoms of general malaise, indigestion, or bowel irregularity. Anorexia is common but not universally present. Alterations in bowel function are highly variable and can include constipation, diarrhea, and even obstruction as a late complication.¹¹ Periumbilical or central abdominal pain generally develop after nonspecific symptoms. If nausea develops, it typically follows the onset of pain.¹² Vomiting may or may not be present. Subjective or objective fever is frequent.

As the clinical course progresses, discomfort migrates to the right lower quadrant. Flank pain, dysuria, or hematuria can occur, given the typical proximity of the appendix to the urinary tract.¹¹

Aggravating and alleviating features can help establish the diagnosis: worsening pain with deep inspiration may be present if there is peritoneal irritation, and individuals may state that the trip to the hospital was painful, particularly when encountering bumps in the road. Such features suggest a peritoneal process is under way. The release of intraluminal obstruction with perforation often results in sudden remittance of pain; consider appendiceal perforation if the patient’s pain has suddenly improved.¹¹

As the natural course progresses, examination findings likewise evolve. Progressive inflammation and peritoneal irritation yield reproducible tenderness to palpation in the right lower quadrant. The exception to right lower quadrant pain is a retrocecal appendix, which does not contact the anterior parietal peritoneum.¹³ Rebound tenderness and involuntary guarding suggest peritonitis. Patients may have costovertebral tenderness, and percussion of the right heel or shaking of the hospital stretcher may elicit abdominal pain. There is no evidence that the digital rectal exam aids significantly in the diagnosis of acute appendicitis.¹⁰ Rovsing’s sign reproduces pain over McBurney’s point as the clinician palpates the descending colon in the left lower quadrant. A positive psoas sign or obturator test suggests an inflammatory peritoneal process. The psoas sign is elicited if abdominal pain is produced with extension of the right leg at the hip while the patient lies on the left side. The obturator test elicits pain with internal and external rotation of the flexed right thigh at the hip. The presence of abdominal rigidity, a positive psoas sign, fever, or rebound tenderness increases the likelihood of acute appendicitis. Prior episodes of similar pain, the absence of right lower quadrant pain, and the absence of classic pain migration make appendicitis less likely. The presence or absence of any exam finding in isolation is neither sufficiently sensitive nor specific to rule out or rule in the diagnosis.

In a systematic review of 42 studies investigating appendicitis in patients aged 18 years or younger, fever was the single most useful sign with an LR(+) of 3.4 (95% confidence interval, 2.4 to 4.8), whereas its absence decreased the likelihood of appendicitis (LR(-), 0.32; 95% CI, 0.16 to 0.64). Rebound tenderness and pain migration to the right lower quadrant were also strong predictors.¹⁴ In comparison, a classic study of exam findings in adult patients showed right lower quadrant pain as the single most useful sign (sensitivity, 0.81; specificity, 0.53; LR(+) 7.31-8.46; LR (-) 0-.28) followed by rigidity and migration of pain. Fever in adults had an LR(+) of 1.94 (95% CI, 0=0.28) of 1.94 (95% CI, 1.63 to 2.32) and a LR(-) of 0.58 (95% CI, 0.51 to 0.67).¹⁵ In both children and adults, however, no historical or physical examination finding is sufficient to rule in or rule out appendicitis.^14,15

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.

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

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

LABORATORY TESTING

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.