A one year-old male beagle dog was obtained from the Animal Facilities of Center for Animal Resources Development, Wonkwang University, Korea. In the previous 3 days, the dog had shown appetite reduction, and the dog was given a health examination. Abdominal sonography and radiography demonstrated abnormal enlargement of the left testicle in the abdominal cavity. Both the retroperitoneal cryptorchid testicle and the other contralateral testicle were removed surgically. The orchidectomized testicles were submitted to gross examination and trimmed. The trimmed tissues was fixed in 10% neutral buffered formalin and embedded in paraffin. Four µm sections were made and stained with hematoxylin and eosin for histopathological examination.

The retroperitoneal cryptorchid testicle was an enlarged, firm and bulging sphere mass (Figure 1A). The cut surface revealed a homogeneous white color (Figure 1B). The contralateral testicle in the scrotum showed an almost normal appearance. Histopathologically, the tumor cells had abundant eosinophilic cytoplasm, round or oval nuclei, and punctuate nucleoli (Figure 2). Malignant behavior was rare. As the results of histopathological analysis, the retroperitoneal cryptorchid testicle was diagnosed as a Sertoli cell tumor.

Testicular neoplasms are frequent in aged dogs [6], with seminoma, Sertoli cell tumors or sertolioma, and Leydig cell tumors being the most prevalent types of testicular neoplasia [6], although cases of mixed germ cell tumors [7] and mesenchymal tumors [8] have been described. Older dogs are commonly affected by testicular enlargement [9], especially in cryptorchid testes, where the incidence of neoplasia is higher compared with scrotal testes [10]. It is common to observe two or more types of neoplasia in the same testicle [4]. A Sertoli cell tumor in the dog is the most prone to produce metastases, occurring in 10 to 14% of the cases. In contrast, seminoma produces metastasis in 6 to 11%, and metastasis from a Leydig cell tumor is extremely rare [4,10]. In this case, metastases were not detected. The more frequent occurrence of these tumors in the right testicle can be accounted for by cryptorchism, which is more common on the right side [4]. The right testicle arises more cranially than the left and has a longer distance to travel to reach the scrotum [4,10]. In this study, the dog revealed unusual cryptorchism in the left testicle. This report describes a case of a Sertoli cell tumor with cryptorchism in a beagle dog.