Background: Cryptorchidism is characterized by the incomplete descent of one or both testicles to the scrotum, being a hereditary alteration and frequently an unilateral condition. Besides the sexual and aggressive behaviour, the retained testicle is commonly located in abdominal cavity, being considered a risk factor for neoplasm development. The most common testicular neoplasm reported in mammalian species are Sertoli cell tumors, Leydig cell tumors, seminomas and teratomas. A presumptive diagnosis of testicular tumor can be achieved by ultrasonography, although the definitive diagnosis is obtained only by histopathology. In this report, we are presenting a case of testicular teratoma in an unilateral abdominal cryptorchid horse. Case: A 3 year-old stallion, American Quarter Horse, was attended and presented a right testicle retained inside the abdomen and a left testicle in the scrotum. Transrectal palpation was used to identify a round and firm structure, presumably the right testicle, lateral to the urinary bladder and located inside abdomen. Further, a transrectal ultrasound examination showed a complex, round mass with irregular edges containing both cystic and solid structures, hypoechoic fluid-filled cavities separated by linear hyperechoic septa. After a clinical examination, the animal was diagnosed with cryptorchidism and was submitted to orchiectomy and cryptorchidectomy by inguinal approach. Surgery was performed under general anesthesia and postoperative care included cold shower, anti-inflammatory and antibiotic therapy. Testicles were surgically removed and further sent for histopathological examination. The visual appearance of the right undescended testicle showed multiple round, cystic, and solid structures on outer surface, while the left descended testicle was apparently normal. The macroscopic evaluation showed that the affected testicle consisted of a firm solid mass with multiple fluid-filled cystic areas. Microscopically, the testicular architecture was replaced by cysts, fibrous tissue, adipose tissue, glandular structures, and foci of calcification. The histology revealed that the retained testicle had a testicular teratoma. Discussion: Reproductive disorders are common in horses and represent a significant part of the equine practitioner routine. Equine cryptorchidism is the most common non-lethal developmental defect of stallions. Surgery is the best treatment, since this alteration is hereditary. Teratomas have been reported more often in cryptorchid testicles, being usually just diagnosed as an incidental finding during surgical procedure. Under field conditions, usually the testicles are not sent for histopathological evaluation and this fact can contribute to underdiagnoses. Ultrasonography allows clinicians to determine testis location, morphological changes in the testes, as well as to elaborate a presumptive diagnose of testicular neoplasm. Histopathology is the best exam to achieve definitive diagnoses in the presence of testicular alterations. In our report, diagnosis of testicular neoplasia was not made before surgery and testicular mass was an incidental finding during pre-surgical examination. In the presence of testicular enlargement or presence of testicular mass, neoplasia should be included in the differential diagnosis. In conclusion, although rare, teratoma should be included in differential diagnoses of retained testicles, especially those with morphological alterations.
