[Testicular Leydig Cell Tumor Incidentally Detected on Computed Tomography : A Case Report].

A 58-year-old man was referred to our department for further evaluation of an incidental right intratesticular mass detected on abdominal and pelvic contrast-enhanced computed tomography performed for an unrelated condition. The mass measured approximately 13 mm and was not clearly palpable on physical examination. Scrotal magnetic resonance imaging showed a well-defined, lobulated, and multinodular mass within the right testis. As a malignant testicular tumor could not be excluded, a right high inguinal orchiectomy was performed for diagnostic and therapeutic purposes. Macroscopically, the excised specimen contained a solid yellow-white mass measuring 16×13×12 mm. Histopathological examination revealed proliferation of tumor cells with round nuclei and eosinophilic cytoplasm. Immunohistochemical staining showed that the tumor cells were positive for calretinin, focally positive for Melan-A, and negative for SALL4. Based on these findings, the diagnosis of a Leydig cell tumor of the testis was made. The patient's postoperative course was uneventful, and no evidence of local recurrence or distant metastasis was observed during 9 months of follow-up. Leydig cell tumors are rare, accounting for approximately 1-3% of all testicular tumors. To our knowledge, this case represents the 128th reported case of testicular Leydig cell tumor in Japan. We report this rare case and provide a review of the literature.