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Appendicitis is acute inflammation of the vermiform appendix, most often due to luminal obstruction, and is the commonest surgical emergency of the abdomen.

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https://www.youtube.com/watch?v=r9amif1DQMc

https://www.youtube.com/watch?v=rTTAnK3PY4A

https://www.youtube.com/watch?v=NNGr9p4c9jo

https://www.youtube.com/watch?v=_HO-HPuE7Ss

Etiopathogenesis

https://www.youtube.com/watch?v=K86eIZyKVmc

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Luminal obstruction → increased intraluminal pressure → venous congestion → ischemia → bacterial overgrowth → inflammation and possible perforation.

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![Proposed pathophysiology of acute appendicitis: The mildest form of appendicitis, phlegmonous uncomplicated appendicitis, is characterized by a transmural invasion of neutrophils. In complicated acute appendicitis, the inflammation and associated vascular thrombosis results in appendiceal wall necrosis (gangrenous appendicitis) progressing to perforation of the appendiceal wall (perforated appendicitis) resulting in either peritonitis (perforation into the free abdominal cavity) or into a localized (peri-appendicular) abscess. The symbol ‘?’ in the figure denotes that it is not comprehensively known which cases of suppurative appendicitis progress to gangrenous and possibly perforated appendicitis and which remain uncomplicated and possibly even resolve spontaneously.

Adapted from Blohs, M. et al. Acute appendicitis manifests as two microbiome state types with oral pathogens influencing severity. Gut Microbes 15, 2145845 (2023) Salminen, P., Haijanen, J., Minneci, P.C. et al. Appendicitis. Nat Rev Dis Primers 11, 79 (2025). https://doi.org/10.1038/s41572-025-00659-6](attachment:6bc4694c-e1f5-4663-a88a-168dbbdac86e:41572_2025_659_Fig4_HTML.webp)

Proposed pathophysiology of acute appendicitis: The mildest form of appendicitis, phlegmonous uncomplicated appendicitis, is characterized by a transmural invasion of neutrophils. In complicated acute appendicitis, the inflammation and associated vascular thrombosis results in appendiceal wall necrosis (gangrenous appendicitis) progressing to perforation of the appendiceal wall (perforated appendicitis) resulting in either peritonitis (perforation into the free abdominal cavity) or into a localized (peri-appendicular) abscess. The symbol ‘?’ in the figure denotes that it is not comprehensively known which cases of suppurative appendicitis progress to gangrenous and possibly perforated appendicitis and which remain uncomplicated and possibly even resolve spontaneously.

Adapted from Blohs, M. et al. Acute appendicitis manifests as two microbiome state types with oral pathogens influencing severity. Gut Microbes 15, 2145845 (2023) Salminen, P., Haijanen, J., Minneci, P.C. et al. Appendicitis. Nat Rev Dis Primers 11, 79 (2025). https://doi.org/10.1038/s41572-025-00659-6

Causes of obstruction:

• Fecalith (most common).
• Lymphoid hyperplasia (esp. in children, after viral infection).
• Rare: parasites (Enterobius vermicularis, Ascaris), tumors (carcinoid, adenocarcinoma), foreign bodies.

Clinical features

https://www.youtube.com/watch?v=kmAnQUMtOXQ

https://www.youtube.com/watch?v=LM2LrQ5oOSQ

Symptoms