[Cellular fibroma of the ovary: description of a case]

Cellular fibromas of the ovary are rare neoplasms belonging to the group of sex-cord stromal tumours. They have been described to show from 1 to 3 mitotic figures per 10 high power fields (HPF) and they generally behave in a benign fashion. Herein we describe the clinicopathological features of a case of ovarian cellular fibroma. The patient, a 22-year-old woman, presented with acute abdominal pain. Laparotomy revealed a large ovarian mass. Histologically the lesion was composed of spindle cells showing slight or moderate pleomorphism and 3 mitoses per 10 HPF. The spindle cells were immunoreactive for vimentin, smooth muscle actin and inhibin alpha-subunit. The differential diagnoses that we considered included the mitotically active leiomyoma because of the strong positivity for smooth muscle actin, but positive immunoreaction with anti alpha-inhibin antibody helped in confirming a sex-cord stromal tumour. Electron microscopy did not show any evidence of smooth muscle differentiation.