The morphology of abdominal and inguinal cryptorchid testes in stallions: a light and electron microscopic study.

Eleven unilateral cryptorchid stallions, two to three years old, were castrated at Louisiana State University Veterinary Teaching Hospital. Five of these cryptorchid cases were abdominal and the rest were inguinal. This study was initiated to document the differences between the abdominal and inguinal equine cryptorchid testes. Specimens were obtained from the abepididymal side of each cryptorchid testes and processed for light and electron microscopic study. The cryptorchid testes were smaller than the scrotal testes, with the abdominal testes being one-fourth the size of the scrotal testes. Two of the abdominal testes had cysts filled with a straw-colored fluid. The seminiferous tubules of the abdominal testes were larger than those in the inguinal testes. The epithelial linings of the seminiferous tubules of the abdominal testes were vacuolated and did not contain more than two layers of undifferentiated cells. The interstitial collagen fibers of the abdominal testes were coarse and more abundant than those of the inguinal testes. The seminiferous tubules of the inguinal testes were smaller and contained many layers of epithelial cells at different stages of embryological differentiation, with scattered primordial germ cells. The necrotic, degenerative changes of the epithelial cells of the abdominal testes were distinct, while the inguinal testes had healthy cells at embryological arrest.