Appendiceal Neuroendocrine Tumours
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Direct answer
Found incidentally in roughly one appendicectomy in a few hundred, the appendiceal neuroendocrine tumour (carcinoid) is the commonest neoplasm of the appendix and behaves far more gently than its midgut cousins. Most arise as yellow submucosal nodules at the tip, are under 1 cm, well differentiated and cured by the appendicectomy that found them. Size drives the surgery: below 1 cm, appendicectomy is complete treatment; beyond 2 cm, or with adverse features, right hemicolectomy is standard. The 1-2 cm zone is the judgement band, where guidelines now favour appendicectomy for low-grade tumours without nodal or mesoappendix involvement. Goblet cell carcinoma is a different disease masquerading under the same organ and always deserves hemicolectomy.
What you must remember
- Epidemiology: 50-85% of all appendiceal neoplasms are neuroendocrine; peak incidence in the fourth decade, no strong sex bias; found in 0.3-0.9% of appendicectomies, most at the tip.
- Location matters: about 70% arise at the tip, 20% at the base — a base lesion risks positive margins and lymphatic spread along the ileocolic chain.
- Size-based surgery: <1 cm — appendicectomy curative (5-year survival above 95%); >2 cm — right hemicolectomy with lymphadenectomy; 1-2 cm — appendicectomy generally adequate for G1 tumours with R0 margins and no mesoappendix invasion beyond 3.5 mm, per current ENETS/NCCN guidance, though older textbooks mandated hemicolectomy.
- Other indications for hemicolectomy: G2/G3 grade, positive base or margin, angioinvasion or lymphovascular invasion, involved mesoappendix, nodal disease.
- Carcinoid syndrome is rare: appendiceal tumours secrete serotonin locally and metastasise to liver so uncommonly that flushing and diarrhoea are exceptional — a favourite "why" question whose answer is absence of hepatic metastases.
- Goblet cell carcinoma (adenocarcinoma ex-carcinoid): mixed neuroendocrine-non-neuroendocrine tumour with signet-ring cells, behaves as an adenocarcinoma, spreads transcoelomically (peritoneal disease), needs right hemicolectomy with cytoreductive surgery where peritoneal disease exists — never managed by simple appendicectomy alone.
- Follow-up: low-risk appendicectomy patients need little beyond 5 years of surveillance; larger tumours follow the general NET pathway with chromogranin A, imaging and octreotide scanning as indicated.
The 1-2 cm decision zone in practice
An appendicectomy specimen from a 32-year-old yields a firm yellow nodule at the tip: well-differentiated neuroendocrine tumour, 1.4 cm, Ki-67 under 2%, margins clear, mesoappendix free of invasion. The surgeon's decision letter must reason through the bands. Under 1 cm the operation was already the cure. Above 2 cm, or if the base were involved, right hemicolectomy removes the regional nodes that the appendicular lymphatics drain towards the ileocolic pedicle. This 1.4 cm tip lesion with all favourable features sits where modern consensus supports simple appendicectomy and structured follow-up — an older exam answer of automatic hemicolectomy for anything above 1 cm has been superseded, and quoting the current thresholds with the adverse-feature list (grade, margin, base, mesoappendix invasion depth, angioinvasion) is what earns the marks. The same specimen stamped "goblet cell carcinoma" would flip the logic entirely: there the neuroendocrine component is decorative, the behaviour is adenocarcinoma, and hemicolectomy with consideration of peritoneal disease becomes the plan.
Where students slip
The classic error is extrapolating midgut carcinoid behaviour — carcinoid syndrome, chromogranin-driven workup — onto a lesion that almost never causes it, and forgetting that the syndrome's absence depends on no hepatic metastasis. The second slip is staging confusion: goblet cell carcinoma handled as an indolent carcinoid undertreats a potentially lethal adenocarcinoma; examiners contrast the two deliberately. Finally, remember the appendix drains portal blood to the liver directly, so the reason for rare syndrome is rare metastasis, not rare serotonin — quoting that chain precisely is the viva-winning formulation.
Frequently asked questions
What is the commonest site of appendiceal carcinoid?
The tip, in about 70% of cases — base lesions are fewer but risk margins and earlier nodal spread.
When is right hemicolectomy indicated?
Tumours above 2 cm, high grade, positive margins or base involvement, deep mesoappendix invasion, angioinvasion or nodal disease; all goblet cell carcinomas.
Why is carcinoid syndrome rare with appendiceal tumours?
Serotonin released by the tumour reaches the liver first through the portal vein, and hepatic metastases — needed for systemic syndrome — are uncommon.
What is goblet cell carcinoma?
A mixed neuroendocrine-non-neuroendocrine tumour with mucin-producing signet-ring cells behaving like adenocarcinoma, requiring hemicolectomy rather than appendicectomy.
What is the prognosis of small appendiceal NETs?
Excellent — tumours under 1 cm treated by appendicectomy carry 5-year survival above 95% with negligible recurrence risk.