Intramucosal fat is uncommon in large bowel polyps but raises three differential diagnoses.

AIMS: This case series intends to expand currently limited knowledge regarding the existence and diagnostic significance of intramucosal fat in colorectal polyps.
METHODS: Clinicopathological features of nine such polyps were reported following histopathological review, including S100 and EMA immunohistochemistry. RESULTS AND
CONCLUSIONS: Such review subdivided seven polyps into three groups: (1) mucosal perineurioma/serrated polyps with fat among the perineurial stroma (three cases); (2) submucosal lipomas with adipose tissue extending into the overlying mucosa (two cases) and (3) polyps with intramucosal adipose tissue only, that is, the newly described but less-recognised entity known as intramucosal lipoma (two cases). The two remaining polyps of this series did not include submucosa but, from assessing their muscularis mucosae, were favoured to represent intramucosal lipomas. The first two phenomena are formally described for the first time by this case series. The last of these three diagnoses should prompt investigations for Cowden syndrome, but intramucosal lipomas are more often sporadic/non-syndromic. © Author(s) (or their employer(s)) 2019. No commercial re-use. See rights and permissions. Published by BMJ.