Histopathological findings in the cryptorchid testes of stallions

Abdominal, inguinal and scrotal testes from 53 horses differing in age were examined by light microscopy including immunohistochemical techniques. Spe rmatogenesis of scrotal testes (controls) starts at the age of 1.5-2 years. By contrast, the development of cryptorchid testes occurs later at the age of 2-3 years. The degenerative alterations affecting the seminiferous tubu les are more distinct in abdominal than in inguinal cryptorchidism. Additio nally the differentiation of the peritubular and intertubular cells is reta rded and disturbed in cryptorchid testes resulting in a deviating expressio n pattern of vimentin, desmin and alpha -actin. Angiosclerosis in equine te stes is a frequent age-related finding and is not associated to the locatio n of the affected testes. Four cases of "testicular regression syndrome" and two cases of an exclusiv e descent of the epididymis are reported. One case of a metastasising semin oma was diagnosed in a unilateral abdominal testis. The findings presented in this study show the possible complexity of alterations in cryptorchidism and, with a view to surgical success, the importance of detailed histopath ological investigation of "abnormal" tissues removed during castration.