They can be seen in any age group, they are generally small solid masses, but they may show cystic areas, hemorrhage, or necrosis. Their sonographic appearance is variable and is indistinguishable from that of germ cell tumors. Sertoli cell tumors are less common, constituting less than 1% of testicular tumors. They are less likely than Leydig cell tumors to be hormonally active, but gynecomastia can occur. Sertoli cell tumors are typically well circumscribed, unilateral, round to lobulated masses. Clinically lymphoma can manifest in one of three ways: as the primary site of involvement, or as a secondary tumor such as the initial manifestation of clinically occult disease or recurrent disease. Although lymphomas constitute 5% of testicular tumors and are almost exclusively diffuse non-Hodgkin B-cell tumors, only less than 1% of non-Hodgkin lymphomas involve the testis. Patients with testicular lymphoma are usually old aged around 60 years of age, present with painless testicular enlargement and less commonly with other systemic symptoms such as weight loss, anorexia, fever and weakness. Bilateral testicle involvements are common and occur in 8.5% to 18% of cases. At sonography, most lymphomas are homogeneous and diffusely replace the testis [Fig. 7]. However focal hypoechoic lesions can occur, hemorrhage and necrosis are rare. At times, the sonographic appearance of lymphoma is indistinguishable from that of the germ cell tumors [Fig. 8], then the patient's age at presentation, symptoms, and medical history, as well as multiplicity and bilaterality of the lesions, are all important factors in making the appropriate diagnosis. Primary leukemia of the testis is rare. However, due to the presence of blood-testis barrier, chemotherapeutic agents are unable to reach the testis, hence in boys with acute lymphoblastic leukemia, testicular involvement is reported in 5% to 10% of patients, with the majority found during clinical remission. The sonographic appearance of leukemia of the testis can be quite varied, as the tumors may be unilateral or bilateral, diffuse or focal, hypoechoic or hyperechoic. These findings are usually indistinguishable from that of the lymphoma [Fig. 9]. Epidermoid cysts, also known as keratocysts, are benign epithelial tumors which usually occur in the second to fourth decades and accounts for only 1–2% of all intratesticular tumors.