In infants, the appendix is a conical diverticulum at the apex of the cecum, but with differential growth and distention of the cecum, the appendix ultimately arises on the left and dorsally approximately 2.5 cm below the ileocecal valve. The taeniae of the colon converge at the base of the appendix, an arrangement that helps in locating this structure at operation. The appendix is freely mobile in the majority and is fixed retrocecally in 16% of adults.

The appendix in children is characterized by a large concentration of lymphoid follicles that appear 2 weeks after birth and number about 200 or more at age 15 years. Thereafter, progressive atrophy of lymphoid tissue proceeds with fibrosis of the wall and partial or total obliteration of the lumen. If the appendix has a physiologic function, it is probably related to the presence of lymphoid follicles.

General Considerations

Approximately 7% of people in Western countries have appendicitis at some time during their lives. With more than 250,000 appendectomies for acute appendicitis performed annually in the United States, it is the most common surgical emergency encountered by the general surgeon and accounts for about 1% of all surgical operations.

Obstruction of the proximal lumen by fibrous bands, lymphoid hyperplasia, fecaliths, calculi, or parasites has long been considered to be the major cause of acute appendicitis. A fecalith or calculus is found in only 10% of acutely inflamed appendices. Though evidence of temporal and geographic clustering of cases has suggested a primary infectious etiology this remains to be proven.

As appendicitis progresses, the blood supply is impaired by bacterial infection in the wall and distention of the lumen; gangrene and perforation occur at about 24 hours, though the timing is highly variable. Gangrene implies microscopic perforation, bacterial contamination of the peritoneum, and peritonitis. This process may be effectively localized by adhesions from nearby viscera.

Clinical Findings

Acute appendicitis may simulate almost any other acute abdominal illness, and in turn may be mimicked by a variety of conditions. Progression of symptoms and signs is the rule—in contrast to the fluctuating course of some other diseases.

A. Signs and Symptoms

Typically, the illness begins with vague midabdominal or periumbilical discomfort followed by nausea, anorexia, and indigestion. The pain is continuous but not severe, with occasional mild cramping. The patient may feel constipated or may vomit. Importantly, within several hours of the onset of symptoms the pain shifts to the right-lower quadrant, becoming localized and causing discomfort on moving, walking, or coughing.

Physical examination shows localized tenderness to palpation and perhaps slight muscular guarding. Rebound or percussion tenderness (the latter provides the same information more humanely) may be elicited in the right-lower quadrant. Rectal and pelvic examinations are likely to be negative; if positive, these more often point to another etiology. The temperature is only slightly elevated in the absence of perforation. Administration of narcotic pain medications does not affect the accuracy of the physical examination.

A common misconception is that inflammation of a retrocecal appendix produces an atypical syndrome. This is incorrect; the clinical findings in this situation are the same as for ordinary (antececal) appendicitis. Acute appendicitis may mimic other surgical diseases if the appendix is located outside the right-lower quadrant (ie, sigmoid diverticulitis, acute cholecystisis, or a perforated ulcer). Even when the cecum is normally situated, however, a long appendix may reach to other parts of the abdomen.

Three general points are worth remembering: (1) people with early (nonperforated) appendicitis often do not appear ill. Finding localized tenderness over the McBurney point is the cornerstone of diagnosis. (2) A rule that will help considerably with atypical cases is never to place appendicitis lower than second in the differential diagnosis of acute abdominal pain in a previously healthy person. (3) Patients with appendicitis most commonly have a history of generalized abdominal that over time becomes focused in the right-lower quadrant.

B. Laboratory Findings

The average leukocyte count is 15,000/μL, and 90% of patients have counts over 10,000/μL. In three-fourths of patients, the differential white count shows more than 75% neutrophils. It must be emphasized, however, that 1 patient in 10 with acute appendicitis has a normal leukocyte count, and many have normal differential cell counts. Appendicitis in HIV-positive patients, while up to three times more common, produces the same syndrome as in healthy adults but the white blood cell count is usually normal.

Urinalysis is typically normal, but a few leukocytes and erythrocytes and occasionally even gross hematuria may be noted, particularly in retrocecal or pelvic appendicitis.

C. Imaging Studies

On plain radiographs localized air-fluid levels, localized ileus, or increased soft tissue density in the right-lower quadrant is present in 50% of patients with early acute appendicitis. Less common findings are a calculus, an altered right psoas shadow, an abnormal right flank stripe, or free peritoneal air (from perforated appendicitis). In general, the findings on plain films rarely aid in diagnosis.

A CT examination of the abdomen may be of help in diagnosis. An enlarged appendix with wall thickening, enhancement, or periappendiceal fat stranding is the most useful CT findings of acute appendicitis. Other findings may be present, including focal cecal thickening, appendicoliths, extraluminal or intramural air, and pericecal phlegmon, but are less reliable. Oral contrast administration is not. CT scans are of greatest value in patients with less than typical clinical and laboratory findings, where a positive study would be an indication for appendectomy. In young adults, low-dose CT is noninferior to standard-dose CT. In the face of typical time course of disease, right-lower quadrant pain and tenderness plus signs of inflammation (eg, fever, leukocytosis), a CT scan would be superfluous and, if negative, even misleading. Ultrasound imaging is generally less reliable than CT, though may become more reliable when done using a combined transabdominal and transvaginal approach. When appendicitis is accompanied by a right-lower quadrant mass, an ultrasound or CT scan should be obtained to differentiate between a periappendiceal phlegmon and an abscess or tumor.

D. Appendicitis During Pregnancy

Appendicitis is the most common nonobstetric surgical disease of the abdomen during pregnancy affecting between 1 in 1400 and 1 in 6600 live births, with cases equally distributed through all three trimesters. By far the most common presentation is right-lower quadrant pain, tenderness, and leukocytosis—the classic syndrome—but the enlarged uterus occasionally will have pushed the appendix into the right-upper quadrant, which gives rise to pain in this location. Some symptoms, such as nausea and vomiting, occur in normal pregnancy, which may obscure accurate diagnosis. Fever is less common than with appendicitis in the absence of pregnancy. The main problem is to recognize appendicitis and perform appendectomy promptly. Both CT and MRI are highly sensitive and specific for the diagnosis of acute appendicitis during pregnancy. Delay in operation runs a higher than usual risk of perforation and diffuse peritonitis, because the omentum is less available to wall off the infection. The mother is in greater jeopardy of serious abdominal infection, and the fetus is more vulnerable to premature labor with complications. Laparoscopic appendectomy is well tolerated by the mother and fetus, but the frequency of technical complications is higher than with the open approach. Appendectomy during pregnancy is often followed by preterm labor but rarely by preterm delivery. Early appendectomy in pregnancy has decreased the maternal death rate to under 0.5% and the fetal death rate to less than 10%. Appendectomy in general does not increase a woman’s risk for infertility later in life.

Diagnosis & Differential Diagnosis