Answer: Sclerosing stromal tumor

Histology: On low power, the neoplasm has a pseudo-lobular pattern made up of cellular nodules separated by edematous connective tissue and dense collagen containing numerous thin-walled vessels. The cellular areas are composed of rounded, vacuolated cells, with eccentric nuclei.

Discussion: Nearly all of sclerosing stromal tumors (SST) occur in the first three decades and all reported cases have behaved in a benign fashion. SST has been associated with virilization secondary to androgen production by the tumor. Histologically this case is classic in its demonstration of the pseudolobular pattern of cellular nodules, composed of fibroblasts and lipid laden cells, and paucicellular areas which can display varying degrees of sclerosis. In addition, this case demonstrated focal positivity for inhibin, although only a minority of tumors has been reported to be immunoreactive for inhibin. Although fibrothecomas with massive edema can have a similar appearance to SST, careful histologic examination and knowing the patient’s age can be extremely helpful. Fibrothecomas are uncommon in the first three decades, where as 80% of SST occur during the second and third decades. In addition, the presence of pseudolobulation and two cell types seen in SST almost always allows a specific diagnosis. Of note, immunohistochemical stains for inhibin will not help with the differential of fibrothecoma or any sex-cord stromal neoplasm versus SST, as all can show positivity for inhibin. The prominent vascularity seen in SST may resemble that seen in hemangiopericytomas. Hemangiopericytomas, however, lack the other distinctive features of SST. The signet-ring type cells in SST can also suggest the diagnosis of a Krukenberg tumor (metastatic signet ring cell carcinoma). However, true signet ring cell carcinomas will contain mucin as opposed to the lipid within the vacuolated cells in the SST. Both a mucin stain as well as an inhibin stain can help with the differentiation of SST from carcinoma.