About 1% of patients seeking care in the ED for abdominal pain have appendicitis, and missed diagnosis and subsequent morbidity continue to occur. The lifetime risk for appendicitis is approximately 9% in men and 7% in women.¹ The classic “textbook” manifestation of appendicitis—right lower quadrant pain, abdominal rigidity, and migration of pain from the periumbilical area to the right lower quadrant—is the exception rather than the norm. Symptoms are frequently atypical, and subtle findings are common. Delayed diagnosis results in a higher risk for perforation, which increases morbidity and mortality. When the diagnosis is delayed, about 20% of appendicitis cases perforate.

Anatomy

The appendix is a tubular structure that arises from the cecum and consists primarily of smooth muscle and an abundance of lymphoid tissue. The average adult appendix can reach a length of 10 cm with a luminal width of 6 to 7 mm. Innervation from sympathetic and vagus nerves accounts for referred pain to the umbilicus when inflammatory changes are present. The location of the appendix (retrocecal, 65%; pelvic, 31%; subcecal, 2%) determines the clinical findings and risk for the development of perforated appendicitis.²

Pathophysiology

Acute appendicitis develops as a result of luminal obstruction, which promotes bacterial overgrowth and distention. Obstruction of the appendiceal lumen is commonly caused by fecal stasis and fecaliths; other obstructive masses include lymphoid hyperplasia, vegetable matter, fruit seeds, intestinal worms, inspissated radiographic barium, and tumors (e.g., carcinoid). Luminal obstruction creates a closed space in which bacterial overgrowth leads to the accumulation of fluid and gas. Organisms are typically polymicrobial, with a predominance of anaerobic and gram-negative species.²

As the appendix distends, normal circulatory supply is impaired and the inflammatory changes worsen. Ischemia, infarction, and perforation can ensue. Progression of an inflamed appendix from gangrene to perforation is variable, with a mean duration of abdominal symptoms of between 2 days (gangrene) and 3 days (perforation).

Clinical Presentations

Classic

The pain of acute appendicitis starts as diffuse, poorly localized, periumbilical discomfort (visceral pain) that localizes to the McBurney point in the right lower quadrant over a period of 12 to 24 hours (peritoneal pain). The McBurney point is located one third of the distance from the right anterior superior iliac crest to the umbilicus. The appendix is located within 5 cm of the McBurney point in only 50% of patients.

Once the pain is perceived in the right lower quadrant, sudden movements cause severe discomfort consistent with localized peritonitis. Associated symptoms often include anorexia, nausea, and vomiting. Diarrhea is uncommon, although patients may report an increasing urge to defecate (the “downward urge”). Bowel movements or the passage of flatus does not relieve the pain, however.

Up to 50% of patients have a normal body temperature on initial arrival at the ED.³ Patients with significant inflammation prefer to remain still in an effort to minimize peritoneal irritation. The right leg may be flexed at the hip to further decrease peritoneal stretch (see Table 39.1, Special Maneuvers That Suggest Appendicitis, online at www.expert.consult.com). Palpation of the abdomen generally reveals localized right lower quadrant tenderness. Rebound tenderness, voluntary and involuntary guarding, and rigidity may be observed, depending on the extent of appendiceal inflammation.

Table 39.1 Special Maneuvers That Suggest Appendicitis

Rovsing sign	With the patient in the supine position, palpation of the left lower quadrant causes pain in the right lower quadrant.
Psoas sign	With the patient in the left lateral decubitus position, extension of the right hip increases pain in the right lower quadrant (when an inflamed appendix is overlying the right psoas muscle).
Obturator sign	With the patient in the supine position, internal rotation of a passively flexed right hip and knee increases right lower quadrant pain.

Physical signs and symptoms vary with the location of the appendix. If the appendix is retrocecal, pain and tenderness may localize to the flank and not to the right lower quadrant. A retroileal appendix in men or boys may irritate the ureter with resulting radiation of pain to the testicle. The gravid uterus of a pregnant patient was previously thought to displace the appendix superiorly as the pregnancy progresses and cause right upper quadrant or flank pain. However, recent studies suggest that this conventional belief may be incorrect and that the location of the appendix may be similar in pregnant and nonpregnant patients.^4,⁵ A pelvic appendix may irritate the bladder or rectum and result in dysuria, suprapubic pain, or a more pronounced urge to defecate. If the appendix is low lying, isolated rectal tenderness may be the only sign.²

Variations

Children

Appendicitis is the most common condition requiring emergency abdominal surgery in children. Up to 8% of children seen in the ED with abdominal pain have appendicitis. In the very young, appendicitis is quite uncommon because the appendix is funnel shaped and less prone to obstruction. Symptoms of appendicitis in this age group are nonspecific and mimic those of gastroenteritis, viral syndrome, and intussusception. The incidence of appendicitis rises with age, but the likelihood of perforation is highest in infants. Neonatal appendicitis has a high mortality rate. Almost 100% of children younger than 2 years have a perforated appendix at the time of diagnosis. In children 3 to 5 years of age the perforation rate is 71%, and in children 6 to 10 years of age the rate is 40%. Appendicitis most frequently occurs in patients between 10 and 20 years old.

Children with appendicitis commonly exhibit fever and vomiting. These two signs, along with abdominal distention, are most often seen in infants. A lethargic, irritable baby with grunting respirations may be a typical manifestation in this age group. Toddlers are more likely to have vomiting and fever followed by pain. In school-age children, vomiting and abdominal pain are the more frequent symptoms.⁶ When the diagnosis is unclear, one should avoid diagnosing acute gastroenteritis in young children without diarrhea.

In the vast majority of children, the diagnosis of appendicitis is made only after perforation occurs, possibly because of a child’s inability to describe the pain or the physician’s misattribution of symptoms to other childhood diseases or to gastroenteritis. As a result of perforation, worsening peritonitis in children might be manifested as lethargy, inactivity, and hypothermia.⁷

Adolescent girls are a subset of the pediatric population that deserves special attention in the evaluation of acute appendicitis. The etiology of right lower quadrant pain in prepubertal and postpubertal girls includes ovarian torsion, ovarian cyst, intrauterine pregnancy, and ectopic pregnancy. A urine pregnancy test followed by pelvic ultrasonography may be helpful in distinguishing ovarian pathology from appendicitis.⁶

Elderly

Elderly patients are often initially seen late in the course of the disease and are three times more likely than the general population to have perforated appendicitis. The elderly have a higher incidence of early perforation (up to 70%) because of the anatomic changes in the appendix that occur with age, such as thinner mucosal lining, decreased lymphoid tissue, a narrowed appendiceal lumen, and atherosclerosis.⁸ A definitive diagnosis is often difficult to make because of associated comorbid conditions and the possibility of immunosuppression. Appendicitis accounts for 7% of abdominal pain in the elderly. Geriatric patients most commonly have an atypical manifestation and delay seeking medical intervention.⁹ In patients older than 70 years, the mortality rate is higher than 20% because of diagnostic and therapeutic delays.¹⁰ The majority of older patients with acute appendicitis are afebrile and do not have leukocytosis. When the clinical, laboratory, and imaging findings are equivocal, a low threshold for surgical consultation and inpatient observation must be considered for elderly patients with abdominal pain.

Pregnant Women

Appendicitis is the most common extrauterine surgical emergency during pregnancy. Diagnosis of appendicitis in pregnancy is difficult because the appendix migrates upward as the uterus enlarges, so the location of pain or tenderness is variable. Early symptoms of appendicitis, particularly nausea and vomiting, are common in pregnancy. Leukocytosis is also a normal finding in pregnancy and does not aid in the differentiation of appendicitis, although an increase in band cells implies the presence of infection.

Pregnancy appears to have a protective effect on the development of appendicitis, especially in the third trimester.² A fetal loss rate of up to 5% is seen in patients with unruptured appendicitis. Maternal death from appendicitis is extremely rare; however, perforation and subsequent peritonitis cause fetal mortality to rise to 30% and maternal mortality to 2%. The use of ultrasonography may differentiate obstetric causes of abdominal pain from appendicitis without the need for imaging studies that involve radiation, such as computed tomography (CT). Once the diagnosis of appendicitis has been made in a pregnant patient, urgent surgical exploration should be performed.¹¹

Nonpregnant Women

Gynecologic causes of lower abdominal pain often mimic appendicitis.¹⁰ Up to 45% of women who appear to have appendicitis on clinical examination are found to have a normal appendix at surgery. The highest percentage of misdiagnosis occurs in women of childbearing age.