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.
Treatment and prognosis
- 1. Pickhardt PJ, Levy AD, Rohrmann CA et-al. Primary neoplasms of the appendix: radiologic spectrum of disease with pathologic correlation. Radiographics. 2003;23 (3): 645-62. Radiographics (full text) - doi:10.1148/rg.233025134 - Pubmed citation
- 2. Ng SS, Lee JF. Mucinous cystadenoma of the appendix. Can J Surg. 2009;52 (2): 158-9. Free text at pubmed - Pubmed citation
- 3. Zagrodnik DF, Rose DM. Mucinous cystadenoma of the appendix: diagnosis, surgical management, and follow-up. Curr Surg. 2003;60 (3): 341-3. doi:10.1016/S0149-7944(02)00728-6 - Pubmed citation
- 4. Lo RH, Kan PS. Appendiceal mucinous cystadenoma presenting as "porcelain" appendix with myxoglobulosis-a rare cause of a right lower quadrant mass. Singapore Med J. 1998;39 (4): 174-6. Pubmed citation
- 5. Honnef I, Moschopulos M, Roeren T. Appendiceal mucinous cystadenoma. Radiographics. 2008;28 (5): 1524-7. Radiographics (full text) - doi:10.1148/rg.285075160 - Pubmed citation
- 6. Wang H, Chen YQ, Wei R et-al. Appendiceal mucocele: A diagnostic dilemma in differentiating malignant from benign lesions with CT. AJR Am J Roentgenol. 2013;201 (4): W590-5. doi:10.2214/AJR.12.9260 - Pubmed citation
- 7. Leonards LM, Pahwa A, Patel MK, Petersen J, Nguyen MJ, Jude CM. Neoplasms of the Appendix: Pictorial Review with Clinical and Pathologic Correlation. Radiographics : a review publication of the Radiological Society of North America, Inc. 37 (4): 1059-1083. doi:10.1148/rg.2017160150 - Pubmed
- 8. Carr NJ, Cecil TD, Mohamed F, Sobin LH, Sugarbaker PH, González-Moreno S, Taflampas P, Chapman S, Moran BJ. A Consensus for Classification and Pathologic Reporting of Pseudomyxoma Peritonei and Associated Appendiceal Neoplasia: The Results of the Peritoneal Surface Oncology Group International (PSOGI) Modified Delphi Process. The American journal of surgical pathology. 40 (1): 14-26. doi:10.1097/PAS.0000000000000535 - Pubmed
- 9. Tirumani SH, Fraser-Hill M, Auer R, Shabana W, Walsh C, Lee F, Ryan JG. Mucinous neoplasms of the appendix: a current comprehensive clinicopathologic and imaging review. Cancer imaging : the official publication of the International Cancer Imaging Society. 13: 14-25. doi:10.1102/1470-7330.2013.0003 - Pubmed
The appendix can be affected by numerous inflammatory, infectious and neoplastic conditions:
- appendiceal mucocoele
neoplasms of the appendix
- appendiceal epithelial neoplasms
- appendiceal neuroendocrine tumours
- appendiceal lymphoma