# Appendix Pathology > FMGE Pathology notes on appendix pathology: obstructive pathogenesis of appendicitis, perforation, carcinoid tumours, goblet cell tumours and pseudomyxoma. - Canonical URL: https://prepelephant.com/topics/fmge/pathology/appendix-pathology - Exam / course: FMGE · Subject: Pathology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Appendix Pathology", PrepElephant, https://prepelephant.com/topics/fmge/pathology/appendix-pathology ## Direct answer Acute appendicitis, the commonest acute abdominal emergency, arises in this organ through a simple mechanical sequence: luminal obstruction by a faecolith, lymphoid hyperplasia or rarely a tumour, continued mucus secretion, rising intraluminal pressure that first occludes lymphatics then veins, bacterial invasion, ischaemic gangrene and finally perforation with peritonitis. Histologically the progression reads mucosal neutrophils, then transmural inflammation, then gangrene with thrombosed mesoappendiceal vessels. Appendices also surprise pathologists: carcinoid tumours are the commonest appendiceal neoplasm, goblet cell adenocarcinoma mimics it in older women, and low-grade mucinous neoplasms seeded into the peritoneum produce pseudomyxoma peritonei, the "jelly belly" of older surgical texts. ## What you must remember - **Pressure sequence:** obstruction → mucus accumulation → luminal pressure exceeding venous pressure → ischaemia → gangrene → perforation; children perforate faster because of a thinner appendix and less omentum. - **Clinical anchors:** migratory pain from periumbilical to right iliac fossa, McBurney point tenderness, and the Alvarado score that quantifies clinical probability. - **Histological progression:** focal mucosal inflammation to transmural neutrophilia; gangrenous appendicitis shows mural necrosis with thrombosed vessels. - **Carcinoid rules:** commonest appendiceal tumour, usually at the tip; under 1 cm is cured by appendicectomy, over 2 cm or with mesoappendiceal invasion warrants right hemicolectomy. - **Goblet cell adenocarcinoma:** older women, signet-ring-like cells infiltrating the wall, prone to ovarian and peritoneal spread — treated as adenocarcinoma, not carcinoid. - **Mucinous disease:** low-grade appendiceal mucinous neoplasm (LAMN) can perforate and seed — pseudomyxoma peritonei with gelatinous ascites, omental caking and "jelly belly". - **Definition discipline:** a pseudocyst has no epithelial lining, a mucocele is a dilated mucus-filled appendix whose nature (retention cyst, LAMN, cystadenoma) only histology settles. ## From perforation risk to an incidental surprise Follow a 22-year-old with 36 hours of classic migratory pain: appendicectomy reveals a gangrenous appendix wrapped by omentum, and histology confirms transmural acute inflammation with serositis — the timeline of obstruction to gangrene compressed into a day and a half. Now the twist every paper loves: the same specimen's tip harbours a 0.8 cm carcinoid tumour with clear margins. Under 1 cm, appendicectomy alone is curative, and the patient needs nothing more; had it measured 2.5 cm or invaded the mesoappendix, a right hemicolectomy discussion would follow. A third scenario completes the picture — a 60-year-old operated for "ovarian cancer" whose peritoneal deposits are mucinous: the appendix, not the ovary, is the usual source, and the diagnosis is pseudomyxoma peritonei from a LAMN, managed by cytoreductive surgery with hyperthermic intraperitoneal chemotherapy in selected centres. One organ, three entirely different diseases, each with a rule attached. ## Where students slip The size cut-offs for appendiceal carcinoid (1 cm and 2 cm) get blurred with gastric and colonic carcinoid rules, and candidates over-treat a 5 mm tip lesion with hemicolectomy. The pseudocyst question loses marks on one word — "devoid of epithelial lining" — which is what separates it from every cystic neoplasm. And when a stem describes a mucocele, remember it is a gross description, not a diagnosis: retention cyst, LAMN and cystadenoma all present as mucoceles and only microscopy separates them. ## Frequently asked questions ### What is the pathogenesis of acute appendicitis? Luminal obstruction stops mucus outflow, intraluminal pressure rises above venous pressure, ischaemia and bacterial invasion follow, culminating in gangrene and perforation. ### How is a 0.8 cm appendiceal carcinoid managed? Simple appendicectomy suffices for tumours under 1 cm with clear margins; right hemicolectomy is reserved for tumours over 2 cm or mesoappendiceal invasion. ### What is pseudomyxoma peritonei? Gelatinous mucinous ascites with omental caking caused by peritoneal seeding, most often from a low-grade appendiceal mucinous neoplasm. ### Why does a pancreatic pseudocyst not qualify as a cyst? It lacks an epithelial lining, being a walled-off collection of enzyme-rich fluid in organised necrotic tissue — the same rule that governs appendiceal mucocele interpretation. ### Which group gets goblet cell adenocarcinoma of the appendix? Typically older women, with signet-ring-like goblet cells infiltrating the wall and spreading to ovary and peritoneum, managed as adenocarcinoma.