Mucinous tumours of the appendix

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

Mucinous tumours of the appendix
Diagnosis in short
Mucinous cystadenoma of the appendix. H&E stain.
LM	mucin, +/- nuclear atypia
Subtypes	see LMDDx
LM DDx	mucinous adenocarcinoma, entrapped mucin, mucinous cystadenoma
Site	appendix
Prevalence	uncommon
Prognosis	dependent on stage and presence/absence of nuclear atypia
Clin. DDx	other appendiceal tumours, metastatic tumours
Treatment	right hemicolectomy or appendectomy (?)

Mucinous tumours of the appendix
External resources
EHVSC	10183

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.
• Many potential pathways for extra-appendiceal spread and peritoneal mucin deposition (pseudomyxoma peritonei)
  • A mucinous neoplasm ruptures the appendix due to expansion by excessive mucin
    • Could occur with either a benign or malignant neoplasm.
  • Malignant mucinous glands infiltrate through the appendiceal wall or enter the lymphatics and spread throughout the peritoneum.
    • Would require a malignant neoplasm.
• Panarelli and Yantiss created a nice summary table - that compares 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 2003 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 of 2003

• 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).
  • mucin extravasation into the appendiceal wall does not upgrade the tumour.
• 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 - low power (SKB)

• 

  Low Grade Appendiceal Mucinous Neoplasm - mucin extravasation into the appendiceal wall- low power (SKB)

• 

  Low Grade Appendiceal Mucinous Neoplasm - mucin extravasation into the appendiceal wall - low power (SKB)

• 

  Low Grade Appendiceal Mucinous Neoplasm - medium power (SKB)

• 

  Low Grade Appendiceal Mucinous Neoplasm - high power (SKB)

• 

  Low Grade Appendiceal Mucinous Neoplasm - low power (SKB)

• 

  Low Grade Appendiceal Mucinous Neoplasm - medium power (SKB)

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.
-- NEGATIVE FOR EXTRA-APPENDICEAL MUCIN.
-- MARGINS NEGATIVE FOR 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.

WHO

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

See also

• Vermiform appendix.
• Mucinous carcinoma.