Mucinous tumours of the appendix

Mucinous tumours of the appendix
External resources
EHVSC	10183

Mucinous tumours of the appendix are uncommon tumours of the vermiform appendix that can have a benign or malignant behaviour.

Benign appendiceal mucocele and appendiceal mucocele redirect here.

General

• There are many classifications and they are controversial.
  • The controversy centres on whether to call all mucinous tumours outside of the appendix adenocarcinoma - regardless of whether they have atypia & show invasion.
• Panarelli and Yantiss created a nice summary table - that compare the classifications - see: comparison of classifications (archivesofpathology.org).
• In women - an ovarian primary must be excluded.
  • Concurrent bilateral ovarian tumours suggests the tumour originated from the appendix and spread to the ovaries.
• The classification by Misdraji et al. is a good starting point if one is unfamilar with the topic, as it is the least complicated.

Misdraji classification

• Benign - low grade mucinous tumour.
• Borderline - mucinous tumour of uncertain malignant potential or borderline mucinous tumour.
• Malignant - mucinous adenocarcinoma.

Five year survival (in a series of 107 cases) as per Misdraji classification:

Tumour	Five year survival
LAMN	100%
LAMN extra-appendiceal spread	86%
MACA	44%

• LAMN = low-grade appendiceal mucinous neoplasm.
• LAMN extra-appendiceal = low-grade appendiceal mucinous neoplasm with extra-appendiceal spread.
• MACA = mucinous adenocarcinoma of the appendix.

World Health Organization classification

WHO classification:

• Adenoma with low-grade dysplasia.
• Adenoma with high-grade dysplasia.
• Low-grade invasive mucinous adenocarcinoma
  • Confined to the appendiceal wall.
  • Outside of the appendix.
• High-grade invasive mucinous adenocarcinoma.

Comparison between Misdraji and WHO classification

Adapted from Panarelli and Yantiss:

Stage	Cytologic dysplasia	Misdraji	World Health Organization
Confined to the mucosa	low-grade	low-grade appendiceal mucinous neoplasm (LAMN)	mucinous adenoma, negative for high-grade dysplasia
Confined to the mucosa	high-grade	non-invasive mucinous cystadenocarcinoma of the appendix	mucinous adenoma with high-grade dysplasia
At least into the submucosa, confined to the appendix	low-grade	low-grade appendiceal mucinous neoplasm (LAMN)	invasive mucinous adenocarcinoma, low-grade
At least into the submucosa, confined to the appendix	high-grade	mucinous adenocarcinoma of the appendix (MACA)	invasive mucinous adenocarcinoma, high-grade
Extra-appendiceal spread	low-grade	low-grade appendiceal mucinous neoplasm (LAMN)	invasive mucinous adenocarcinoma, low-grade
Extra-appendiceal spread	high-grade	mucinous adenocarcinoma of the appendix (MACA)	invasive mucinous adenocarcinoma, high-grade

Microscopic

Low-grade appendiceal mucinous neoplasm

• AKA benign mucinous tumour of the appendix.

Microscopic:

• Single layer of epithelium with tufts.
  • Vaguely resemble serrations, i.e. the saw-tooth pattern in hyperplastic polyps of the colon.
• Mucin contained (inside appendix only).
• No marked nuclear atypia.

Note:

• May be deceptively bland appearing from a cytologic perspective.

Images

www:

• LAMN - low mag. (nature.com).
• LAMN - high mag. (nature.com).
• Appendiceal mucocele (pathlabmed.typepad.com).

• 

  Mucinous cystadenoma - low mag. (WC)

• 

  Mucinous cystadenoma - intermed. mag. (WC)

• 

  Mucinous cystadenoma - high mag. (WC)

• 

  Mucinous cystadenoma - high mag. (WC)

• 

  Mucinous cystadenoma - very high mag. (WC)

Low-grade appendiceal mucinous neoplasm with extra-appendiceal spread

• AKA mucinous borderline tumour of the appendix.

Microscopic:

• Same as LAMN but mucin outside of the appendix.
• Cells in mucin, i.e. cellular mucin.

Mucinous adenocarcinoma of the appendix

• AKA malignant mucinous tumour of the appendix.

Microscopic:

• Marked nuclear pleomorphism.
• Invasion into the appendiceal wall.

Sign out

LAMN

VERMIFORM APPENDIX, APPENDECTOMY:
- LOW-GRADE APPENDICEAL MUCINOUS NEOPLASM.
- ACUTE APPENDICITIS.
- ACUTE PERIAPPENDICITIS. 

VERMIFORM APPENDIX AND CECUM, APPENDECTOMY WITH CECAL CUFF:
- LOW-GRADE APPENDICEAL MUCINOUS NEOPLASM (MUCINOUS CYSTADENOMA).
- MARGINS NEGATIVE FOR MUCINOUS NEOPLASM.

COMMENT:
No extra-appendiceal mucin is identified. There is no invasion into the appendiceal wall.

APPENDIX, APPENDECTOMY:
- APPENDICEAL MUCINOUS CYSTADENOMA WITH EXTENSIVE CALCIFICATION.
-- NEGATIVE FOR HIGH-GRADE DYSPLASIA.
- NEGATIVE FOR MALIGNANCY.

See also

• Vermiform appendix.
• Mucinous carcinoma.