Acute appendicitis remains one of the most common diseases treated by the general surgeon. Appendectomy (appendicectomy in the UK) is the most common acute care operation performed in the United States, with 341,000 appendectomies performed in 2006. Americans have a 7% lifetime risk of developing appendicitis. Mortality associated with acute appendicitis and its treatment has dropped from 26% historically to as low as 0.2 deaths per 100,000. Mortality for patients with perforated appendicitis, multiple comorbidities, and at the extremes of age, however, may approach 5% or even higher in some cases.

The appendix is a diverticulum of the cecum and averages about 10 cm in length and 3 to 5 mm in width. The appendix derives its blood supply from the appendiceal artery, a terminal branch of the ileocolic artery or, on occasion, off the right colic artery. Thought to be a vestigial organ, the appendix is now known to have some immunologic function, especially with the secretion of the immunoglobulin A (IgA), a mucosal surface antibody.

The pathophysiology of acute appendicitis is related to luminal obstruction. Fecaliths are the most common cause of luminal obstruction, present in nearly 50% of patients with acute appendicitis and even greater numbers in patients with gangrenous appendicitis. Other causes of luminal obstruction include lymphoid hyperplasia, malignancy, or rarely parasitic infection. Luminal obstruction has also been reported from ingested foreign bodies such as nails, screws, gum, cherry pits, and teeth. Obstruction at the appendiceal orifice with continued mucosal secretions results in venous congestion, tissue ischemia, and tissue infarction. Bacterial overgrowth occurs resulting in suppuration and localized inflammatory phlegmon formation, exacerbating the tissue injury. The clinical spectrum of appendicitis, therefore, begins with simple (or uncomplicated) appendicitis progressing toward suppurative and phlegmonous appendicitis, then toward gangrenous appendicitis and finally to perforated (or ruptured) appendicitis with eventual abscess formation. Spontaneous resolution or transient improvement with antibiotics and subsequent recurrent appendicitis has been described in the literature, mostly occurring within 1 year of symptoms.

Traditionally, appendicitis is considered a clinical diagnosis. The classic presentation was described by Reginald Fitz, who coined the term “appendicitis,” in 1886 and codified by Zachary Cope in 1921. Appendicitis is more common in younger men with the highest incidence between 10 and 30 years of age, but may occur in men and women of any age.

The classic presentation begins with vague periumbilical or sometimes epigastric pain of visceral nature from a dilated appendix that migrates to the right lower quadrant and becomes somatic in nature from contact of the serosa of the inflamed appendix against the parietal peritoneum. The periumbilical pain is classically followed by anorexia, nausea, and occasionally vomiting. Fever may follow, but is inconsistent, present only in 40% of patients with appendicitis. The migratory nature of the pain that settles clearly at McBurney’s point (one-third of the distance from the anterior superior iliac spine to the umbilicus) is one of the most specific signs of appendicitis. The Alvarado Scale is one of a number of clinical quantification scores of the most common signs and symptoms of appendicitis.

Other signs of peritoneal inflammation are more variable and include percussion tenderness, Rovsing’s sign (right lower quadrant pain elicited by palpation of the left lower quadrant), and Dunphy’s sign (increased abdominal pain with coughing). The uncommon psoas sign (pain on extension of the right hip) suggests retrocecal appendicitis and the rare obturator sign (pain on internal rotation of the right hip) when present suggests pelvic appendicitis. Perforated appendicitis may present with more severe abdominal pain, progressing from focal peritonitis to generalized peritonitis with rebound, voluntary guarding, followed by involuntary guarding, and finally rigidity.

The time course is variable, but typically becomes progressively worse from 12 to 48 hours. Seventy-five percent of patients present within 24 hours of symptoms. Pediatric and geriatric patients are more likely to present later and with perforation. Risk of rupture in adult patients is variable, but at 36 hours of symptoms is ∼2% and left untreated may increase about 5% every 12 hours. Other literature suggests no increased risk of perforation, especially if antibiotics are administered at the time of diagnosis.

An elevated WBC count is classically present, but may be normal in nearly one-third of adults with appendicitis, and in up to 80% of patients with <24 hours of pain. A left shift or an increase in polymorphonuclear leukocytes, neutrophilia, and bandemia are typically present. C-reactive protein (CRP), often used in Europe in the workup of abdominal pain is often elevated in adults but is not as reliable in children. Pyuria and RBCs on a urinalysis may be seen with appendicitis. A very high WBC count (>20,000) may suggest perforation.

While appendicitis is traditionally a clinical diagnosis, computed tomography (CT) scan has >95% accuracy for the diagnosis of appendicitis and is being used with increasing frequency. CT criteria for appendicitis include an enlarged appendix >6 mm in diameter, appendiceal wall thickness >2 mm (sometimes called the target sign), periappendiceal inflammation (fat stranding), the presence of a fecalith, and occasionally the presence of the arrowhead sign (thickened cecum funneling contrast toward the appendiceal orifice). CT scans of the abdomen and pelvis are typically performed with oral and IV contrast, though recent evidence suggests nearly equivalent results without oral or IV contrast. Some centers offer appendiceal CT scan, performed after instillation of gastrografin per rectum and requiring only one-third of the radiation exposure of standard abdominopelvic CT scans with high accuracy. Ultrasound is not as accurate as CT, but may be useful to avoid ionizing radiation exposure, especially in pregnant women and children. The
risk of radiation-induced malignancy has been recently estimated at 0.18% following exposure to abdominal CT. Magnetic resonance imaging (MRI) may be useful for the pregnant patient with suspected appendicitis and an indeterminate ultrasound. Negative appendectomy rates have been steadily declining, with historic rates of 10% to 40%, now as low as 5% when imaging is used.

In a patient with a history of chronic abdominal pain, bloody diarrhea, or a family history of inflammatory bowel disease, Crohn’s ileitis should be considered. CT scanning will often show evidence of ileal inflammation. Gynecologic pathology such as mittelschmerz, salpingitis, ectopic pregnancy, tubo-ovarian abscess, and endometriosis may be elicited on physical examination and may often be apparent on CT scan. A history of diarrhea and vomiting without migratory or focal right lower quadrant pain may suggest gastroenteritis. Meckel’s diverticulitis may mimic appendicitis but is usually distinguished on CT scan. Pelvic inflammatory disease (PID) can present similarly to appendicitis. History and physical examination may be helpful in distinguishing the two, though some women with appendicitis may also exhibit adnexal and cervical motion tenderness. A history or a recent upper respiratory infection with poorly localized abdominal pain in a child may suggest acute mesenteric adenitis. The uncommon epiploic appendagitis, torsion, and thrombosis of a pedunculated adipose structure off the serosal surface of the cecum may resemble appendicitis but can be distinguished on CT scan. Finally, the rare familial Mediterranean fever (FMF) may masquerade as perforated appendicitis with diffuse peritonitis, but lacks CT findings of appendicitis and is often diagnosed only after laparotomy.