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Wednesday, October 9, 2013

Cryptorchidism in a dog

Keywords: 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:

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Other cells appeared to be binuclear or were in a state of mitosis, a phenomenon not normally visible in seminiferous epithelium:

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The significant of these findings is not certain but again they may be associated with the peripuberal status of this dog.

The prostate gland shown here

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From what can be seen in this interactive histology preparation, of a normal male dog (click on Guest to log in automatically) the glands in this dog were probably inactive i.e. there was no prostatic fluid within the gland in the sections shown above. A word of caution: When one views the cross section of a normal canine prostate gland, it should be noted that secretions accumulate in collecting ducts towards the center of the gland. Therefore it is possible that the sections shown here were too superficial within the gland to show secretions.  My thanks to Dr David Sims, a colleague here at the AVC for that interactive preparation. Incidentally David informs me that the measuring tool was not programmed for that preparation so any measurements will be meaningless.

In summary, no conclusions could be drawn as to the normalcy of the prostate in this dog.

Notes: Cryptorchidism is a common problem in dogs, especially the toy breeds. The mode of heritability is not clear but, in some breeds, it has been associated with an autosomal recessive gene.

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.