A Developmental Concept of Equine Cryptorchism1

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Abstract
Fifty equine fetuses and 13 foals were dissected to observe normal and abnormal testicular descent. The findings were correlated with observations on cryptorchid horses to establish the importance of the developmental factors contributing to cryptorchism. By developmental processes previously described, the testis is surrounded by the peritoneal cavity, suspended from the dorsal body wall, by a broad thin mesorchium and is connected to the groin by the gubernaculum and posterior gonadal (epididymal) ligament. Expansion of the vaginal process around the gubernaculum because of continuous pressure of peritoneal fluids results in tension on the gubernaculum, drawing the testis to the internal inguinal ring. Enlargement of gubernaculum and epididymal ligament stretches the inguinal canal, allowing passage of the testis through the canal, normally between 300 days of gestation and 10 days after birth. The left testis frequently lags as much as 6 cm behind the right testis in descent, so is more likely to be locked in the abdominal cavity by fibrosis of the internal ring after brith. The testis passes through the inguinal canal, not retroperitoneally to it. An understanding of testicular descent provides a basis for diagnosis and surgical correction of various types of cryptorchism. Cryptorchism may be diagnosed by rectal and scrotal palpations, considering the position of the vas deferens in the inguinal ring and the mass of gubernaculum preceding the testis into the scrotum.

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