Canine cryptorchid dissection
Keywords: cryptorchid, canine, dissection, anatomy
The dissected specimen; a young German Shepherd Dog cryptorchid on its left side.
Salient parts of the dissection specimen are keyed in color below. Of special interest is the clearly visible mesodeferens (MD) adjacent to the retained testicle (RT). It would be much longer (caudal-to-cranial) if the testicle had descended into the scrotum on that side. The epididymis (EP) of the retained testicle and the retained testicle itself are clearly visible without any dissection because they are not covered by a vaginal tunic, specifically a visceral layer of a vaginal tunic. Obviously, there is no vaginal tunic in the abdomen. The descended testicle (DT) is however, covered by the visceral layer of the vaginal tunic and for that reason, it cannot be seen without further dissection in this specimen.
The descended testicle serves as reminder for normal anatomy. The parietal vaginal tunic (PVT) is shown in green below, cut away and folded back towards the top of the image, revealing the red vascular bundle (V) that contains the spermatic artery and vein and the blue ductus deferens (DD). Both of these structures and the testicle itself of course, are revealed here because they lie in the vaginal cavity. The reader is reminded however that although they are visible, they are in fact, covered with the visceral layer of the vaginal bursa (a small point for the anatomic purist!). On the other hand, a very practical point is the location of the ductus deferens on the medial side of the testicle. This means that the ductus can be reached most easily for vasectomy by entering the medial side of the vaginal cavity and even more easily from the cranial aspect of the scrotum than the caudal aspect. This is because the mesorchium can interfere with entry to the medial cavity if a caudal approach is adopted. Although dogs are seldom vasecomized, this anatomy holds true for any carnivore, wild or domestic. In fact, it holds true for all mammals.
The ductus deferens can be seen entering the abdomen through the inguinal canal (the yellow ring). The bladder (B) is colored yellow here, as are the ureters (U) .From the kidneys, each ureter travels caudally dorsal to the ductus deferens (DD) on each side then they enter the bladder.
This dissection is of course centered around the fact that this dog was a hemi-cryptorchid. The testicles will be retained, weighed and histopathology will be conducted on the retained testicle. As is usually the case, it is expected that the spermatogenesis will be absent in the retained testicle but present in the scrotal testicle. Even here, the retained testicle appears to be smaller than the descended testicle. Those images & data are pending.
Retained testicles in dogs become neoplastic at a rate that is 8 to 10 times higher than for descended testicles. Usually these are Sertoli cell tumors. For this reason, they are usually removed surgically. Diagnosis of cryptorchidism revolves around clinical signs and the use of ultrasonography, hCG stimulation paired with testosterone assay and more recently, antimullerian hormone (AMH) assay.
