Low-grade appendiceal mucinous neoplasm
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At the time the article was created Yuranga Weerakkody had no recorded disclosures.View Yuranga Weerakkody's current disclosures
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Low-grade appendiceal mucinous neoplasms (LAMN), previously known as appendiceal mucinous cystadenomas, are rare mucinous tumors of the appendix showing low-grade cytologic atypia, cf. high-grade appendiceal mucinous neoplasms.
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Considerable controversy still exists on mucinous neoplasms of the appendix pathologic classification and nomenclature 9. According to a panel of specialist review in 2016, new nomenclature and classification for the appendiceal mucinous neoplasms based on their histologic type and biologic behavior 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 acute appendicitis. Around 25% of patients can be asymptomatic 2.
Symptoms are more likely to be present if a tumor has perforated and complicated with pseudomyxoma peritonei.
It is characterized 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 mucocele.
Histologically these tumors 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, periappendiceal fat stranding and intraperitoneal free fluid is nonspecific.
The following three features are more suggestive of malignancy 6:
- soft tissue thickening (internal soft tissue attenuation nodularity of mucoceles)
- wall irregularity
- pseudomyxoma peritonei
Treatment and prognosis
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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