atypical polypoid adenomyoma atypical polypoid adenomyoma atypical polypoid adenomyoma (apa) is a rare benign tumour of the uterus. atypical polypoid adenomyomamicrograph of an atypical polypoid adenomyoma. h&e stain.specialtypathology pathology apas are characterized by glands with abnormal shapes that: (1) often have squamous metaplasia, and (2) are surrounded by benign smooth muscle. nuclear atypia, if present, is mild. the microscopic differential diagnosis includes endometrial carcinoma and endocervical adenocarcinoma. intermed. mag. very high mag.