Low-grade appendiceal mucinous neoplasm

Case contributed by Dr Bruno Di Muzio


Two days history of right iliac fossa pain.

Patient Data

Age: 35 years

Abdomen and pelvis

There is what appear to represent a blind-ended large tubular structure filled with fluid located in the right iliac fossa. It is suspected this is in continuity with the large bowel, therefore, representing a grossly enlarged appendix. Trace of free fluid is identified. 

Liver has mildly increased echogenicity suggesting steatosis but is otherwise normal. The biliary tree, gallbladder, spleen, and kidneys are normal. 


Abdomen and pelvis

CT confirms a large appendiceal mucocele pointing upwards with lobulation and rims of calcification at its apex. Adjacent free fluid and the clinical presentation concern for rupture. No free gas. No evidence of metastatic deposits. 

Microscopy: The sections were taken through the appendiceal wall show obliteration of the submucosa, with mucinous epithelial lesion with a villiform architecture resting directly on the muscularis propria. The lining cells show nuclear crowding and mild stratification, coarse nuclear chromatin and tall apical cytoplasm containing mucin. There is the preservation of polarity to the basement membrane.  The lumen contains large quantities of focally calcified, acellular mucin.  At the site of rupture, acellular mucin dissects through the wall of the appendix and is present at the serosal surface, with an associated serosal reaction including mesothelial hyperplasia, a florid fibroblastic response and fibrin deposition on the serosal surface. Acellular mucin is also seen in the extruded material sampled over the appendiceal tip. Focally at the tip, mucin at the serosal surface contains clusters of low-grade neoplastic epithelial cells. Foci of chronic inflammation, including clustered lymphocytes, scattered multinucleated giant cells and granulomatous inflammation, are present within the wall. In areas, dense fibrosis replaces mural structures, including the muscularis propria, and there is acellular dissecting mural mucin.The lesion is clear of the proximal and distal margins, and there are no other mucosal abnormalities. There is no metastatic disease in regional lymph nodes.

Conclusion: Ruptured low-grade appendiceal mucinous neoplasm (LAMN), 90mm; low-grade dysplastic epithelium within extra-appendiceal mucin; negative resection margins; no metastatic disease in 20 regional lymph nodes.

Case Discussion

Low-grade appendiceal mucinous neoplasms, previously known as appendiceal mucinous cystadenomas, are rare mucinous tumors of the appendix showing low-grade cytologic atypia. On imaging, the features are those of an appendiceal mucocele.   

This case illustrates the presentation due to rupture. 

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Case information

rID: 78592
Published: 9th Jun 2020
Last edited: 7th Aug 2020
Inclusion in quiz mode: Included

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