Neuroendocrine tumour of the appendix

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Neuroendocrine tumour of the appendix is a common tumour of the vermiform appendix. It is also known as appendiceal neuroendocrine tumour, abbreviated appendiceal NET.

It was previously known as appendiceal carcinoid.


  • Most common tumour of the appendix.[1]
    • Not really common though - one is seen in approximately 300 appendectomies.[2]


    • Often found incidentally, may be microscopic.
    • May cause obstruction leading to mucocele or acute appendicitis.
    • May precipitate torsion.

Size matters in appendiceal NETs:[3]

  • <1.0 cm - do not metastasize.
  • 1.0-2.0 cm - rarely metastasize.


  • Simple resection, e.g. appendectomy, sufficient for most tumours <2 cm.[4][5]


  • Classically found in the tip of the appendix.
  • Characteristic yellow cut surface post-fixation.
  • Circumscribed but not encapsulated.
  • Firm (due to desmoplasia).
  • Centred in the submucosa.
  • Nodules that do not usually cause erosion of the overlying mucosa.




  • Classically subepithelial/mural.
  • Various growth patterns:
    • Nested (insular).
    • Trabecular.
    • Palisading.
    • Ribbons, rosettes.
  • Fibrous stroma in between cell groups.
  • Cytomorphology:
    • Monotonous appearance with scanty mitoses.
    • Round central nuclei.
    • Stippled chromatin (AKA salt-and-pepper chromatin and coarse chromatin).
    • Eosinophilic granular cytoplasm.


Special Types

  • Tubular carcinoid.
    • Neuroendocrine cells forming tubules (no cell nests).
    • Some tubules can contain mucin.
    • Can be confused with adenocarcinoma.
    • Features suggesting tubular carcinoid (over adenocarcinoma):
      • Arises from base of crypts, with no disruption of surface epithelium.
      • No associated epithelial precursor (no adenomatous change).
      • Neuroendocrine cytologic features, without prominent atypia.
      • IHC (NE markers +ve).
  • Goblet cell carcinoid - dealt with in the article crypt cell carcinoma.
  • Signet-ring cells forming glandular structures.
  • Possibly also with extra-cellular mucin.[citation needed]






  • CK7 and CK20 variable.[6]

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Vermiform Appendix, Appendectomy:
     - Low-grade neuroendocrine tumour (carcinoid tumour), see comment.
     -- Margins clear. 
     -- Please see synoptic report.
     - Perforated acute appendicitis with periappendicitis.

The tumour stains as follows:
POSITIVE: AE1/AE3, chromogranin A, synaptophysin, CD56.
NEGATIVE: CK7, CK20, S100.

The low-grade neuroendocrine tumour (in the planes of section) is in the tip and 
separate from the appendiceal perforation site/acute appendicitis.

The specimen was submitted in total.

See also


  1. Mitchell, Richard; Kumar, Vinay; Fausto, Nelson; Abbas, Abul K.; Aster, Jon (2011). Pocket Companion to Robbins & Cotran Pathologic Basis of Disease (8th ed.). Elsevier Saunders. pp. 435. ISBN 978-1416054542.
  2. Mitra, B.; Pal, M.; Paul, B.; Saha, TN.; Maiti, A. (2013). "Goblet cell carcinoid of appendix: A rare case with literature review.". Int J Surg Case Rep 4 (3): 334-7. doi:10.1016/j.ijscr.2013.01.007. PMID 23416502.
  3. Modlin, IM.; Lye, KD.; Kidd, M. (Feb 2003). "A 5-decade analysis of 13,715 carcinoid tumors.". Cancer 97 (4): 934-59. doi:10.1002/cncr.11105. PMID 12569593.
  4. Nussbaum, DP.; Speicher, PJ.; Gulack, BC.; Keenan, JE.; Ganapathi, AM.; Englum, BR.; Tyler, DS.; Blazer, DG. (May 2015). "Management of 1- to 2-cm Carcinoid Tumors of the Appendix: Using the National Cancer Data Base to Address Controversies in General Surgery.". J Am Coll Surg 220 (5): 894-903. doi:10.1016/j.jamcollsurg.2015.01.005. PMID 25840530.
  5. Fornaro, R.; Frascio, M.; Sticchi, C.; De Salvo, L.; Stabilini, C.; Mandolfino, F.; Ricci, B.; Gianetta, E.. "Appendectomy or right hemicolectomy in the treatment of appendiceal carcinoid tumors?". Tumori 93 (6): 587-90. PMID 18338494.
  6. Matsukuma, KE.; Montgomery, EA. (Jul 2012). "Tubular carcinoids of the appendix: the CK7/CK20 immunophenotype can be a diagnostic pitfall.". J Clin Pathol 65 (7): 666-8. doi:10.1136/jclinpath-2011-200639. PMID 22461652.