Metastatic seminoma with regression of testicular primary: ultrasonographic detection.

We report a case of seminoma of the testis metastatic to the retroperitoneum. Biopsy of the retroperitoneal mass revealed anaplastic seminoma. No testicular mass could be palpated. Testicular ultrasonography showed a hypoechoic 3 X 2 cm. area in the left testis suggestive of a primary testicular tumor, most likely a seminoma. Histological evaluation of the resected testis revealed fibrous tissue but no definable tumor.