Chapter 81: Acute Appendicitis

INTRODUCTION AND EPIDEMIOLOGY

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.

PATHOPHYSIOLOGY

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

CLINICAL FEATURES

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 ...