Answer: Sclerosing stromal tumor

Histology: At low power this tumor has a pseudolobular pattern with loose connective tissue and edema between the cellular nodules. The tumor also has a staghorn (Hemangiopericytoma-like) vascular pattern. The cellular component of the nodules mainly consists of round cells with vacuolated cytoplasm and fibroblast-like cells. No mitotic figure is seen.

Discussion: Sclerosing stromal tumor (SST) of the ovary occurs predominantly in young women. EM study has revealed that the cells in SST are a mixture of luteinized theca like cells, fibroblast like cells, smooth muscle cells, and primitive mesenchymal cells. Sometimes one can see cells resembling signet-ring cells. One study has shown that a variable portion of tumor cells in all cases studied have trisomy 12. As far as the prognosis is concerned, limited follow-up data indicate that this is a benign lesion.

The differential diagnosis includes tumors with a hemangiocytoma-like vascular pattern such as solitary fibrous tumor, hemangiopericytoma, low grade endometrial stroma sarcoma etc. If necessary, immunostains can be performed to exclude these possibilities but the histology of this case is typical of sclerosing stromal tumor.

Reference(s):
– Kawauchi S, Tsuji T, Kaku T, Kamura T, Nakano H, Tsuneyoshi M. Sclerosing stromal tumor of the ovary: a clinicopathologic, immunohistochemical, ultrastructural, and cytogenetic analysis with special reference to its vasculature. Am J Surg Pathol. 1998; 22(1):83-92.