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low-grade appendiceal mucinous neoplasm

Wednesday 18 May 2016

LAMN / mucinous neoplasms of the appendix, LAMNs



- Low-grade appendiceal mucinous neoplasm (LAMN) : Macroscopy

- Low-grade appendiceal mucinous neoplasm (LAMN) : Microscopy

- Typical undulating and flattened epithelium resting on fibrous stroma in appendiceal LAMN


- Villous or occasionally flat proliferation of mucinous epithelial cells originating from appendiceal lumen.
- Lesional cells typically demonstrate abundant apical mucin with elongated nuclei and low grade nuclear atypia (LAMN); however, nuclei may appear compressed.
- Often associated with atrophy of underlying lymphoid tissue, crypt loss and effacement of muscularis mucosae.
- Broad dissection of mucin, epithelium or both may occur with potential involvement of extra-appendiceal surface, an important finding affecting prognosis.
- Extra-appendiceal mucin incites a serosal reaction and may contain neovascularization, assisting in differentiation from benign transfer of mucin during gross examination.

Ovarian metastasis

Features in favor of metastatic LAMN
- Bilaterality
- pseudomyxoma peritonei
- subepithelial clefts
- scalloped glands
- pseudomyxoma ovarii
- tall cells

Differential diagnosis

- HAMN : High grade appendiceal mucinous neoplasm (HAMN):

  • lesion arising in appendix with high grade epithelial features in the absence of infiltrative growth
  • high grade nuclei (HAMN)
  • may show convoluted architecture, including micropapillary architecture or cribriform architecture

- teratoma-associated mucinous tumors

See also

- appendiceal tumors

- appendix

  • appendiceal pathology / pathology of the appendix

Open references

- Mucinous neoplasms of the appendix: a current comprehensive clinicopathologic and imaging review. 2013. doi : 10.1102/1470-7330.2013.0003