Adenomyofibroma of the endometrium with skeletal muscle differentiation

A case of adenomyofibroma with skeletal muscle differentiation is described. A 55-year-old asymptomatic woman had atypical glandular cells of undetermined significance on a routine Papanicolaou smear. The endometrial biopsy revealed fragments composed of benign endometrial glands and myofibromatous stroma with foci of skeletal muscle differentiation. The stroma exhibited focal mild cytologic atypia and hypercellularity without periglandular cuffing or mitoses. Electron microscopy and immunohistochemical staining for myoglobin confirmed the skeletal muscle differentiation. A diagnosis of low-grade adenosarcoma with heterologous differentiation was made in the biopsy specimen based on the atypical stroma, the skeletal muscle differentiation, and previous observations that adenosarcomas may contain bland areas indistinguishable from an adenofibroma. The patient underwent hysterectomy, bilateral salpingo-oophorectomy, and pelvic lymphadenectomy. The hysterectomy specimen revealed small foci of residual tumor. In light of these findings the diagnosis was revised to adenomyofibroma with skeletal muscle differentiation. Uterine adenomyofibroma with skeletal muscle differentiation should be distinguished from a low-grade adenosarcoma in an endometrial biopsy.