Appendicitis: Overview, Anatomy, and Clinical Management

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Introduction

The vermiform appendix is a small, finger-like projection from the cecum, primarily known for its tendency to become inflamed, leading to acute appendicitis. This condition is the most common cause of acute abdominal pain requiring surgical intervention, particularly in young adults. Appendicectomy (or appendectomy) is one of the most frequently performed emergency surgeries and is often the first major procedure undertaken by surgical trainees. Despite advancements in diagnostic imaging, the diagnosis of appendicitis remains largely clinical, relying on a combination of patient history, physical examination, and surgical judgment.

The appendix, once considered a vestigial organ, may play a role in immune function and maintaining gut microbiota. For example, appendicectomy has been associated with a reduced risk of ulcerative colitis, suggesting a potential interaction between the appendix, intestinal flora, and immune regulation.

Anatomy of the Appendix

The appendix is a narrow, blind-ended tube connected to the cecum, measuring approximately 7.5–10 cm in length. It consists of mucosal, submucosal, muscular, and serosal layers. The base of the appendix is consistently located at the confluence of the three taeniae coli of the cecum. The position of the appendix, however, can vary:

  • Retrocecal: Behind the cecum (most common, ~74% of cases).
  • Pelvic: Extending into the pelvis (~21% of cases).
  • Subcecal or Paracecal: Less common positions.

The mesoappendix, a fold of peritoneum, attaches the appendix to the terminal ileum and contains the appendicular artery, a branch of the ileocolic artery. Thrombosis of this artery can lead to ischemia and necrosis of the appendix. The appendix is also rich in lymphatic tissue, particularly in younger individuals, which may contribute to its susceptibility to inflammation.

Epidemiology and Etiology

  1. Incidence: Acute appendicitis affects approximately 300,000 individuals annually in the U.S., with the highest incidence in those aged 10–19 years. The lifetime risk of developing appendicitis is about 9%.
  2. Causes: The primary cause is obstruction of the appendiceal lumen, often due to:
    • Fecaliths: Hardened fecal matter.
    • Lymphoid Hyperplasia: Enlargement of lymphatic tissue, commonly seen in younger individuals.
    • Tumors or Strictures: Rare causes, more common in older adults.
  3. Pathophysiology: Obstruction leads to increased intraluminal pressure, impaired venous drainage, and bacterial overgrowth. This results in inflammation, ischemia, and, if untreated, perforation. Perforation can lead to localized abscess formation or diffuse peritonitis.

Clinical Presentation of acute appendicitis

  1. Symptoms:
    • Abdominal Pain: Classically begins as vague, colicky periumbilical pain (visceral pain) and later localizes to the right lower quadrant (RLQ) as somatic pain develops.
    • Anorexia, Nausea, and Vomiting: These symptoms often follow the onset of pain.
    • Fever: Low-grade fever is common, though high fever (>38.5°C) in children may suggest alternative diagnoses.
  2. Signs:
    • Tenderness: Maximal at McBurney’s point (one-third the distance from the anterior superior iliac spine to the umbilicus).
    • Rebound Tenderness: Pain upon sudden release of pressure in the RLQ.
    • Rovsing’s Sign: RLQ pain elicited by palpation of the left lower quadrant.
    • Psoas Sign: Pain on extension of the right hip, suggesting a retrocecal appendix.
    • Obturator Sign: Pain on internal rotation of the flexed right hip, indicating pelvic appendicitis.

Diagnosis

  1. Physical Examination:
    • Tenderness, guarding, and rebound tenderness in the RLQ are hallmark findings.
    • Rectal examination may reveal tenderness in cases of pelvic appendicitis.
  2. Laboratory Tests:
    • White Blood Cell Count: Often elevated (>10,000 cells/μL).
    • C-Reactive Protein (CRP): May be elevated.
    • Urinalysis: Helps rule out urinary tract infection.
  3. Imaging:
    • CT Scan: The gold standard for diagnosis, showing appendiceal wall thickening, fat stranding, or fecaliths.
    • Ultrasound: Preferred in children and pregnant women, though less sensitive in obese patients or those with retrocecal appendices.
    • MRI: Used in pregnant women when ultrasound is inconclusive.

Pathology

Acute appendicitis begins with luminal obstruction, leading to increased intraluminal pressure, venous congestion, and bacterial invasion. This progresses to mucosal ulceration, ischemia, and, ultimately, perforation. Perforation can result in localized abscess formation or diffuse peritonitis, depending on the appendix’s position and the body’s ability to wall off the infection.

Treatment

  1. Nonoperative Management:
    • Antibiotics alone are inferior to surgery, with a recurrence rate of 39.1% within 5 years (based on the APPAC trial).
    • Reserved for select patients with uncomplicated appendicitis or contraindications to surgery.
  2. Surgical Management:
    • Laparoscopic Appendectomy: The preferred approach, involving three small incisions and removal of the appendix using a stapler or energy device.
    • Open Appendectomy: Performed via a transverse incision over McBurney’s point, particularly in cases of perforation or abscess.
  3. Perforated Appendicitis:
    • Managed with IV antibiotics and percutaneous drainage of abscesses if >2 cm.
    • Interval appendectomy may be recommended in patients over 30 due to the risk of underlying malignancy.

Summary

Acute appendicitis is a common surgical emergency characterized by migrating abdominal pain, anorexia, and RLQ tenderness. Diagnosis relies on clinical evaluation supported by imaging. Prompt surgical intervention remains the standard of care, though nonoperative management is an option in select cases. Understanding the anatomy, pathophysiology, and clinical features of appendicitis is essential for accurate diagnosis and effective treatment.

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