Rete Testis-Associated Nodular Steroid Cell Nests

Abstract

A putative hilus interstitial cell has been proposed as the cell of origin for testicular tumors of adrenogenital syndrome, but its normal histology is not documented. We present hitherto undescribed nodular steroid cell nests associated with the rete testis that are distinctive in their morphology and immunohistochemical profile from Leydig cells and do not have the morphology of typical extra-adrenal cortical rests. These nodules measured 1, 1, 1.8, 2, and 2.5 mm in size with a distinct sinusoidal vasculature. Individual cells were rounded to polygonal with evenly distributed moderate-to-abundant eosinophilic cytoplasm. The nuclei were homogenous and round, with fine chromatin and ocasionally with prominent nucleoli. The differential diagnosis included adrenocortical rests, testicular adnexal Leydig cells, carcinoid tumorlets, paraganglionic rests, and adenomatoid mesothelial proliferation. Immunohistochemistry showed positivity for melan A (5/5), inhibin (3/5), and calretinin (2/4), although the immunoreactivity was distinctively different from the concurrent intratesticular Leydig cells and testicular adnexal Leydig cells in all cases. The unique morphology, immunophenotype, and distinctive location of these cells in the testicular mediastinum raises the possibility that these cells represent testicular hilus steroid cells, the putative histogenetic cell implicated for testicular tumors of adrenogenital syndrome. We propose to name these proliferations rete testis-associated nodular steroid cell nests.