EIN in Endometrial Polyps

The Problem: EIN can occur within a Polyp!!  Nonetheless, caution should be exercised not to misdiagnose benign endometrial polyps. Features of benign polyps that can overlap with EIN include a cytology different than that of the normal functionalis, and low volume percentage stroma caused by cysts (senile polyps) or randomly aggregated glands.  

Benign polyps: Usually have a regularly irregular distribution of glands.   Dominant cysts, especially those lined by bland or atrophic epithelium are common in older patients.  Cytologic variation does not usually appear in geographic clusters of glands, but is interspersed.  Apparent gland aggregates have a cytology similar to more dispersed glands.  See Below.

EIN arising within a polyp. In general, all criteria for usual EIN diagnosis apply to EIN arising within a polyp,  but with the caveat that the reference point for interpretation of EIN cytology and architecture are the background polyp itself, not the normal endometrial functionalis.  EIN within polyps are best recognized as geographic regions of contiguous glands with an architecture and cytology readily distinguished from that of the background polyp.  See Below.

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