Adenomatous hyperplasia of the rete testis in the undescended testis.

Multiple foci of micronodular or tubulopapillary structures were noted in the rete testis of 13 cases of undescended testes. These structures were lined by low columnar to cuboidal epithelium, showed back-to-back crowding, and were supported by a thin lamina propria. These changes, referred to as adenomatous hyperplasia of the rete testis, appear to be a frequent finding in the undescended testis. An age-matched control group did not show any of these features.