Atypical Endometrial Hyperplasia : Morphology
Atypical Endometrial Hyperplasia/Endometrioid Intraepithelial Neoplasia (AEH/EIN) is composed of densely packed glands (seen on the left) that are cytologically and architecturally distinct from the non-atypical glands in the adjacent endometrium (seen on the right). The focus must be >1 mm in a single linear dimension (usually > 5-10 glands). Do not combine two separate foci to meet the size criterion for EIN.
For assessing gland:stroma ratio, squamous morular areas are not included. Various artifacts, including gland telescoping or artifactual displacement of glandular epithelium may cause focal increase in gland density but they will lack the cytologic changes of a true AEH/EIN. One must also exclude other benign mimics and adenocarcinoma.