Appendicitis - types according to etiology, pathogenesis and forms of inflammation. Tumors of the appendix - epithelial, neuroendocrine
The appendix is a normal true diverticulum of the cecum, it is prone to chronic and acute inflammation.
Acute appendicitis
- Most common in adolescents, 7% prevalence across life
- Etiology due to progressive increases in intraluminal pressure that compromises venous outflow. Many cases are also associated with luminal obstruction (by fecaliths or gallstones)
- Subserosal vessels are congested, with perivascular infiltrate in all layers of the wall. Gross visual changes show a dull, granular appearing erythematous surface. In more severe cases focal abscesses may form (acute suppurative appendicitis) which may create hemorrhagic ulcerations and gangrenous necrosis, often followed by rupture
- Clinical observation is localised pain in the right lower quadrant with nausea, vomiting and low grade fever. Deep tenderness is found at McBurney’s point, known as McBurney's sign.
Gross: acute appendicitis in a 10-year-old boy, cut lengthwise – the appendix is swollen and sausage-shaped, with red, inflamed mucosa around the lumen and a thickened, pale wall.
Image: “Acute Appendicitis” by Ed Uthman from Houston, TX, USA, CC BY 2.0, via Wikimedia Commons.
Remember: the forms follow each other – catarrhal (superficial, mucosa only) → phlegmonous (suppurative; neutrophils through the whole wall) → gangrenous → perforation with peritonitis or a periappendiceal abscess. The histological diagnosis of acute appendicitis needs neutrophils in the muscularis propria.
Tumours of the appendix
- Most common is the carcinoid tumor, often discovered incidentally
- Adenomas or non-mucin-producing adenocarcinomas can also occur in the appendix and may cause obstruction and enlargement that mimics acute appendicitis