From the archives of the AFIP: tumors and tumorlike lesions of the testis: radiologic-pathologic correlation.

Testicular carcinoma represents only 1% of all neoplasms in men, but it is the most common malignancy in the 15-34-year-old age group. Germ cell tumors constitute 95% of all testicular tumors. Germ cell tumors are a varied group of neoplasms whose imaging features reflect their underlying histologic characteristics. Seminomas are generally well-defined homogeneous lesions, whereas the nonseminomatous tumors (embryonal carcinoma, yolk sac tumor, choriocarcinoma, teratoma, and mixed germ cell tumor) have a much more varied appearance. Germ cell tumors follow a predictable pattern of spread via the lymphatic drainage to the retroperitoneal nodes. Choriocarcinoma, which has a proclivity for early hematogenous spread, is a notable exception. Testicular tumors may also arise from the sex cords (Sertoli cells) and stroma (Leydig cells). Although 90% of these tumors are benign, there are no reliable imaging criteria to differentiate them from malignant masses. Some benign testicular masses can be recognized, obviating an unwarranted orchiectomy. A dilated rete testis is a normal variant and appears as a series of small tubules near the mediastinum testis. Other benign lesions that can be suspected on the basis of imaging findings and history include intratesticular cysts, epidermoid cysts, congenital adrenal hyperplasia, and sarcoidosis.