Paratesticular fibrous pseudotumor: a morphologic and immunohistochemical study of 13 cases.

Paratesticular fibrous pseudotumor is a rare intrascrotal fibrous proliferation for which numerous synonyms have been proposed. Immunohistochemical staining was done in 13 cases identified by a database search (2000 to 2008) at our institution. All men (19 to 75 y old, mean 41.9 y) presented with scrotal masses, 6 patients also had hydroceles. Six men were treated by orchiectomy, whereas the remaining 7 men underwent excisional biopsy. Histologically, lesions were subdivided into 3 types: (1) "plaque-like" consisting of dense fibrous tissue with clefts without significant inflammation identical to a pleural plaque (5 cases); (2) "inflammatory sclerotic" with dense fibrous tissue containing lymphocytes (diffusely or aggregates or germinal centers), plasma cells, and an increased capillary network (6 cases); and (3) "myofibroblastic" consisting of reactive looking tissue-culture-like spindle cells with numerous capillaries and sparse chronic inflammation (2 cases). Stains for smooth muscle actin were positive in 11/13 (84.6%) cases, whereas desmin was positive in 4/13 (30.8%) cases. Stains for cytokeratin AE1/AE3, calretinin, and CD34 were positive in 7/13 (53.8%), 6/13 (46.2%), and 7/13 (53.8%) cases, respectively. All cases were negative for beta-catenin and ALK-1. Ki-67 showed a proliferation index of <1% in all but 2 cases, which had 5% labeling. Although there were 3 distinct histologic patterns seen in paratesticular fibrous pseudotumors, their immunohistochemical profile had overlapping features. Paratesticular fibrous pseudotumor looks histologically distinct from fibromatosis and inflammatory myofibroblastic tumor (IMT) seen in other organs, an assertion supported by negative stains for beta-catenin and ALK-1, respectively. However, as not all IMTs react with ALK and we had only 2 cases with a myofibroblastic appearance, we cannot definitively exclude the possibility that this subtype of paratesticular fibrous pseudotumor is related to IMT. Although this lesion has different histologic patterns, presently it is not warranted to split it into 3 separate entities as all share the same clinical presentation, are biologically benign, and lack consistent immunohistochemical differences.