Low-grade appendiceal mucinous neoplasm

Low-grade appendiceal mucinous neoplasms (LAMN), previously known as appendiceal mucinous cystadenomas, are rare mucinous tumours of the appendix showing low-grade cytologic atypia, c.f. high-grade appendiceal mucinous neoplasms.

Considerable controversy still exists on mucinous neoplasms of the appendix pathologic classification and nomenclature 9. According to a panel of specialist review in 2016, a new nomenclature and classification for the appendiceal mucinous neoplasms based on their histologic type and biologic behaviour has been proposed. The previously known term "appendiceal mucinous cystadenomas" is no longer recommended, being replaced by “low-grade appendiceal mucinous neoplasm” 7-8.

They may be histologically present in around 0.3% appendiceal resection specimens 3

A commonly described clinical presentation is right iliac fossa pain, similar to that of an acute appendicitis. Around 25% of patients can be asymptomatic 2

Symptoms are more likely to be present if a tumour has perforated and complicated with pseudomyxoma peritonei

It is characterised by villous adenomatous changes of the appendiceal epithelium associated with marked distension of the appendiceal lumen with mucin. This can typically result in an appendiceal mucocoele.

Histologically these tumours show low-grade cytologic atypia associated with at least one of the following 7-8

  • loss of the muscularis mucosae 
  • fibrosis of the submucosa
  • rupture of the appendix
  • mucin and/or tumoral cells outside the appendix

Differentiation between cystadenoma and cystadenocarcinoma of the appendix can be difficult. Size, density and wall thickness of these mucoceles can be similar between the two groups. Furthermore, calcification, internal septations, peri-appendiceal fat stranding and intraperitoneal free fluid is nonspecific.

The presence of:

  • soft tissue thickening (internal soft tissue attenuation nodularity of mucoceles)
  • wall irregularity
  • pseudomyxoma peritonei

have been shown to be the most specific markers in differentiating between benign and malignant groups with these three features more suggestive of malignancy 6.

Staging and management of these are different from those of colorectal carcinoma, please refer to the appendiceal mucinous neoplasms TNM staging for further details. ​

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Article information

rID: 23740
Section: Pathology
Tag: cases
Synonyms or Alternate Spellings:
  • Mucinous cystadenoma of appendix
  • Appendiceal mucinous cystadenomas
  • Mucinous cystadenoma of the appendix
  • Mucinous cystadenomas of the appendix
  • Appendiceal mucinous cystadenomas

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