Testicular seminoma: clinical, imaging, and histologic features in nine horses.

Equine testicular seminoma carries a poor long-term prognosis due to high metastatic potential, even after castration.

This retrospective case series describes the clinical, ultrasonographic, and histopathologic features of testicular seminoma in nine horses evaluated at a referral hospital between 2000 and 2024. The median age at diagnosis was 18 years (range 8–26). Three horses presented with systemic signs including colic and ventral edema, had large abdominal masses on rectal palpation, and were euthanized following diagnostic evaluation. The remaining six horses presented with unilateral testicular enlargement (n=5) or during cryptorchid castration (n=1). All six underwent castration, and histopathology confirmed malignancy with lymphatic neoplastic emboli in the excised testes. Despite surgical intervention, five of these six horses were euthanized 4 months to 3 years post-castration due to acute weight loss and confirmed metastatic abdominal masses. One horse was euthanized for unrelated reasons. Notably, negative imaging at the time of diagnosis did not preclude subsequent metastatic disease, highlighting the insidious nature of this tumor. The authors recommend comprehensive diagnostic screening—including transabdominal and transrectal ultrasonography—at diagnosis and at frequent intervals thereafter, regardless of initial findings. Histopathologic findings including lymphatic emboli should raise immediate concern for metastatic potential. Overall, testicular seminoma in horses carries a poor long-term prognosis due to high rates of metastatic spread, regardless of whether the affected testis is descended or retained.

This summary was distilled by AI and may occasionally misinterpret data. Confirm critical details with the primary literature before clinical application.