Cryptorchidism in a dogKeywords: canine, cryptorchid, testicle
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The reproductive tract of a seven month old border Collie (hit-by-car). This dog had a well developed prostate gland and os penis and the penile frenulum had almost disappeared. The frenulum is visible here as the thin, clear membrane on the ventral part of the extended penis. All these are signs of adequate androgen production. The left testicle was retained in the abdomen. Note how much smaller the left testicle is than its counterpart; mainly due to the absence of spermatogenesis. See histology below.
One should remember however, that the effect of cryptorchidism on steroidogenesis is for all practical purposes, negligible.
The right testicle was present in the scrotum but was separated from the rest of the ductus deferens when the tract was retrieved. The missing section of the ductus deferens is indicated here by the dotted line. To illustrate the fact that the ductus deferens runs medially and caudally in normal descended testicles (and indeed in this case too), it has been rotated clockwise (green arrow) to show that anatomy. The parietal vaginal clinic (PVT) has been stripped away from the descended testicle in order to show these structures. In the retained testicle of course, there is no vaginal clinic around the testicle therefore the testicle and epididymis are immediately visible.
The histology of the testicles is shown below:
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The upper image is that of the cryptorchid testicle. Interstitial cells (Leydig cells) and germ cells (spermatogonia) are present but there is no active spermatogenesis. In fact the tubules are in greater disarray than expected if one is accustomed to equine cryptorchid histology (another species where cryptorchidism is common).
The lower image shows that spermatogenesis was proceeding to spermiation in some tubule cross sections in the descended testicle. The author was struck by the relative lack of tubule cross sections in which spermiation was occurring. This may have been associated with the fact that this dog was only seven months old and therefore only on the verge of puberty. Also, besides being sparse, spermatogenesis was not normal in this testicle. Large cells resembling hypertrophic secondary spermatocytes were present in some tubules. Also present were cells that contained extremely compact, basophilic nuclei. These are shown below:
The risk of neoplasia in retained testis has been reported to be 9 to 14 times higher than in the scrotal testis with Sertoli cell tumors and seminomas being the most common tumors. Due to the fact that the testicles in dogs do not descend until birth or shortly thereafter, one should not confirm a diagnosis of cryptorchidism until a dog is at 4 months of age, especially in view of the fact that prepuberal testicles are sometimes very difficult to feel in dogs.