hyperplasia simple endometrial hyperplasia MONDO:0006410 UMLS:C0456483 SCTID:198324001 EFO:1000525 ICD9:621.31 NCIT:C35463 MEDGEN:96819 A proliferation of endometrial cells resulting in glandular enlargement and budding without changes in the basic structure of the endometrium. Epithelial atypia may be present or absent.