Neuroendocrine tumour of the appendix

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.

General

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

Presentation

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

Size matters in appendiceal NETs:

• <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 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.

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 and coarse chromatin).
  • Eosinophilic granular cytoplasm.

DDx:

• Colorectal adenocarcinoma.
• Adenocarcinoid.
• Crypt cell carcinoma, also known as 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).

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]}

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)

www:

• Appendiceal carcinoid (humpath.com).
• Carcinoid of the appendix (brown.edu).
• Appendiceal carcinoid (flickr.com/Qiao).

IHC

Features:

• Chromogranin A -ve/+ve.
• Synaptophysin +ve.
• Keratin positive, but CK7/CK20 negative.^{[citation needed]}
• S100 positive for appendix.^{[citation needed]}

See also

• Vermiform appendix.
• Neuroendocrine tumours.