Neuroendocrine tumour of the appendix

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Neuroendocrine tumour of the appendix is a common tumour of the vermiform appendix.

General

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

Presentation

    • 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.

Gross

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

Image

  • Appendiceal neuroendocrine tumour. (WC)

Microscopic

Features:

  • 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, 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 aka Crypt cell carcinoma
  • Signet-ring cells forming glandular structures,
  • Possibly also with extra-cellular mucin

DDx:

  • Colorectal adenocarcinoma.
  • Adenocarcinoid.
  • Crypt cell carcinoma (goblet cell carcinoid).
  • Metastatic adenocarcinoma.
  • Normal ganglion cells in the Meissner plexus (submucosa) and Auerbach plexus (located between the inner and outer layers of the muscularis propria).

Images

  • Appendiceal carcinoid with torsion of the appendix - 1x (SKB)

  • Appendiceal carcinoid with torsion of the appendix - low power (SKB)

  • Appendiceal carcinoid with torsion of the appendix - medium power (SKB)

  • Appendiceal carcinoid - low power (SKB)

  • Appendiceal carcinoid - high power (SKB)

  • Appendiceal carcinoid - synaptophysin (SKB)

  • Appendiceal carcinoid - low power (SKB)

  • Appendiceal carcinoid - high power (SKB)

  • Appendiceal carcinoid - low power (SKB)

  • Appendiceal carcinoid with necrosis (SKB)

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IHC

Features:

  • Chromogranin A -ve/+ve.
  • Synaptophysin +ve.
  • Keratin positive, but CK7/CK20 negative
  • S100 positive for appendix

See: '.

See also

References

  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.
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