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The Appendix

  1. Anatomy
    The vermiform appendix, which is usually 8 to 10 cm in length, typically has a retrocecal attachment to the cecum, but its tip is generally not fixed and can therefore move freely. It is invested with a mesentery, the mesoappendix. Q The wall of the appendix is composed of the same layers as the rest of the intestine. The most prominent microscopic feature is the predominance of submucosal lymphoid tissue, which develops in early infancy, reaches its largest size during adolescence and then progressively atrophies.
  2. Appendicitis:
    1. Acute appendicitis is an inflammatory disease of the wall of the vermiform appendix that leads to transmural inflammation and perforation and peritonitis.
    2. This condition is by far the most common disease of the appendix and is the most frequent cause of an abdominal emergency.
    3. Although incidence peaks in the second and third decades, acute appendicitis may occur in persons of any age.
  3. Pathogenesis
    1. Acute appendicitis relates to obstruction of its orifice, with secondary distention of the lumen and bacterial invasion of the wall. Mechanical obstruction by fecaliths or solid fecal material in the cecum is found in one third of cases.
    2. Occasionally tumors, parasites such as Enterobius vermicularis or foreign bodies are incriminated. Lymphoid hyperplasia due to bacterial or viral infection (e.g., by Salmonella or measles) may obstruct the lumen and lead to appendicitis.
    3. However, no obstruction is demonstrated in up to half of patients with appendicitis, and the factor that precipitates the disease in these patients is unknown.
    4. As secretions distend an obstructed appendix, intraluminal pressure increases and eventually exceeds the venous pressure. This causes venous stasis and ischemia,and leads to mucosal ulceration and invasion by intestinal bacteria.
    5. Neutrophil accumulation produces microabscesses. Interestingly, appendectomy protects against development of ulcerative colitis but not Crohn disease.
  4. Pathology
  1. The appendix is congested, tense, and covered by a fibrinous exudate. Its lumen often contains purulent material. A fecalith may be evident.
  2. Microscopically, early cases show mucosal microabscesses and a purulent exudate in the lumen. As infection progresses, the entire wall becomes infiltrated with neutrophils, which eventually reach the serosa. Q Perforation of the wall releases the luminal contents into the peritoneal cavity.
  3. The complications of appendicitis are principally related to perforation, which occurs in one third of children and young adults. 

Clinical Features:

  1. Acute appendicitis is typically manifested as epigastric or periumbilical cramping pain, but the pain may be diffuse or initially restricted to the right lower quadrant.
  2. Shortly thereafter, nausea and vomiting occur and the patient develops a low-grade fever and moderate leukocytosis.
  3. Several conditions that do not require surgery may be misdiagnosed as appendicitis, especially mesenteric adenitis in children, Meckel diverticulitis, rupture of an ovarian follicle during ovulation and acute salpingitis.
  1. Mucocele
  1. Mucocele refers to a dilated mucus-filled appendix.  Q
  2. The pathogenesis may be neoplastic or non-neoplastic.  Q
  3. In the non-neoplastic variety chronic obstruction leads to retention of mucus in the appendiceal lumen. Q
  4. Most mucoceles are associated with neoplastic epithelium. In the presence of a mucinous cystadenoma or a mucinous cystadenocarcinoma, the dilated appendix is lined by a villous adenomatous mucosa.
  5. Cystadenocarcinoma exhibits infiltrating neoplastic glands into the wall of the appendix.
  6. A mucocele which results from mucus secretion by a cystadenoma or cystadenocarcinoma of the appendix, perforation may lead to seeding of the peritoneum by mucus-secreting tumor cells, a condition known as pseudomyxoma peritonei. In less than one third of cases, pseudomyxoma peritonei is caused by disease of the appendix; in half, it originates from ovarian mucinous cystadenocarcinoma.


  1. Carcinoid tumors of the appendix are common.
  2. They are unlikely to metastasize unless they are over 1.5 cm, which is very rare.

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