Endometrial stromal nodule, light micrograph. An endometrial stromal nodule is a benign lesion composed of endometrial stroma, usually seen in middle-aged women. It resembles low-grade endometrial stromal sarcoma; however, it is sharply circumscribed and does not invade blood vessels, lymphatics or myometrium. This high magnification view shows a uniform population of small, round to oval cells with scant cytoplasm, closely resembling normal endometrial stroma. There is no cytologic atypia and mitotic activity is low.