Complex multilocular cystic lesion of rete testis, accompanied by smooth muscle hyperplasia, mimicking intratesticular Leydig cell neoplasm.

Non-neoplastic smooth muscle cell proliferation occurs under a variety of circumstances in many body organs. These abnormalities have been described as hypertrophy, hyperplasia or hamartomatous proliferations. In the male genital system, the excessive growth of smooth muscle in spermatic cord or paratesticular tissue is rare. In previously described cases, these lesions presented as masses but lacked the microscopic features of a neoplasm. We describe a complex multilocular cystic lesion composed of cystic transformation of the rete testis associated with smooth muscle proliferation mimicking intratesticular Leydig cell neoplasm. The lesion consists of three separate components: (1) cystic dilatation of the rete testis; (2) diffuse, interstitial smooth muscle proliferation with intraseptal expansion; and (3) extensive stroma with myxoid areas and scattered interstitial Leydig cells. These morphological findings, supported by a wide immunohistochemical panel, are consistent with cystic dilatation of the rete testis associated with smooth muscle hyperplasia, most probably of myoid origin. To the best of our knowledge, no similar complex lesion of the rete testis has yet been reported.