Seminoma in a dog.
Keywords: neoplasia, testicle, canine, seminoma.A mixed breed stray dog weighing 42 Kg was presented for routine castration.
As shown here, the right testicle was substantially enlarged. Note that neither the nipples nor prepuce (a homolog of the vulva lips) were swollen in this dog. Therefore the possibility of a Sertoli cell tumor was considered unlikely.
Image size: 2000 x 1333px
Ultrasonography of the right testicle showed a solid mass with numerous strong acoustic interfaces throughout the tissue. This mass was presumed to be a neoplasm.
Image size: 640 x 480px
Ultrasonography of the left testicle showed strong acoustic interfaces (white arrow) similar to those in the right testicle. These lay adjacent to a more homogeneous echodense area (yellow arrows) within the stroma.
Image size: 640 x 480px
Transabdominal ultrasonography showed the prostate to be moderately enlarged.
Image size: 2000 x 1435px
The cut surface of the right testicle was pale yellow-white in color with multiple lobules of what was presumed to be neoplastic tissue. As seen below, a dark brownish-red area was present in the center of the lobulated mass. Histologic examination showed this to be a neoplastic mass similar to the rest of the mass, but more highly vascularized.
Image size: 3000 x 2402px
Interestingly, neoplastic tissue was also present in the left testicle, explaining the diffuse areas of increased echo-density and the highly echogenic acoustic interfaces seen in this testicle on ultrasonography.
Image size: 3000 x 3266px
Histolopathology of the right and left testicles was similar. The whitish-yellow tissue masses were semininomas. The entire right testicle had been replaced by a seminoma. In the left testicle (inset image below) seminiferous tubules were still present between the neoplastic masses but spermatogenesis was absent in those seminiferous tubules. Only spermatogonia and Sertoli cells were present. The inset image also shows how one particular mass was separated from non-neoplastic tissue by a fibrous tunic. This was not true of all the tumor masses in this case.
Image size: 1200 x 970px
The main image above shows a histological section that is typical of a seminoma i.e. large sheets of closely packed cells with little supporting stroma. Occasional lymphocytic infiltrations (shown below),
Image size: low resolution: 680 x 512px
were also seen within these sheets of cells; again typical of a seminoma. It should be noted that the diffuse distribution of this seminoma probably represents an advanced stage of neoplasia; less advanced stages being intra-tubular, then intratubular and diffuse.
Image size: 1360 x 1024px
As seen here, the tumor cells were large and polyhedral with marked differences in the size and shape of the nuclei (anisokaryosis). As is usual for this tumor, nuclei often contained more than one prominent nucleolus. The mitotic index was low in all the tumor nodules.
Note: Like Sertoli cell tumors, seminomas develop far more frequently in cryptorchid testicles than descended testicles and usually do not metastisize. Unlike Sertoli cell tumors, which produce estrogens and cause feminization, seminomas are not known to produce hormones. Therefore the absence of spermatogenesis in the intact tubules in this case cannot be easily explained.
Seminomas occur bilaterally in about 20% of cases therefore their bilateral occurrence here was not remarkable.
As mentioned, seminomas are usually benign in dogs and orchidectomy is curative. In rare cases, seminomas may metastasize to the skin, eyes, brain and thoracic and abdominal organs. Owners should probably be informed of that possibility.
The authors thanks Mr Matthew Powers AVC 2015, for bringing this case to his attention and Dr Aisha Young for performing the ultrasonography.
References:
Looijenga. L.H. et al 1994. Seminomas of the canine testis. Counterpart of spermatocytic seminoma of men? Lab Invest. 1994.71:490-496
Grieco, V. 2008 Canine Testicular Tumours: a Study on 232 Dogs. J. Comparative Pathology 138:86–89
http://www.uoguelph.ca/~rfoster/repropath/male/dog/maledog_testis.htm
