Small Leydig cell tumors usually present as well-defined homogeneously hypoechoic lesions, often located peripherally in the testis, with prominent vascularization at color Doppler interrogation. They are often more echogenic compared to seminoma (Fig. 40.3). Large-cell calcifying Sertoli cell tumors are usually echogenic masses with large areas of calcifications, or extensively calcified lesions. Non-calcifying Sertoli cell tumors are typically hypoechoic, well-circumscribed, round to lobulated masses. The ultrasonographic appearance of the other histotypes is not specific.

While primary testicular tumors usually present as a mass-forming lump that enlarges destroying and replacing the normal parenchyma, the hallmark of lymphoma and other infiltrating neoplasms, such as plasmacytoma, is an infiltrative growth pattern in which tumor cells surround and compress the seminiferous tubules and the normal testicular vessels. Focal lymphomatous involvement presents on ultrasonography as single or multiple hypervascular lesions of decreased echogenicity. In diffuse lymphomatous infiltration, the testis is globally enlarged, with decreased echogenicity and marked hypervascularization, mimicking inflammation (Fig. 40.4). Identification of normal testicular vessels with a regular course crossing the lesion is a relatively specific feature characterizing lymphomas and other infiltrative tumors from mass-forming lesions. In a recent series of 43 pathologically proven testicular lymphomas, color Doppler ultrasonography demonstrated normal testicular vessels within the tumor in 72 % of cases [3]. Although color Doppler ultrasonography is able to differentiate between infiltrative and mass-forming tumors, nonneoplastic diseases such as chronic granulomatous orchitis and other inflammatory conditions may have similar appearance. Therefore, differential diagnosis may be difficult in the absence of clinical signs and symptoms of inflammation.

The ultrasonographic appearance of leukemic and lymphomatous infiltration is similar to primary lymphoma. Mass-forming metastatic deposits are very rare, often indistinguishable from primary neoplasms (Fig. 40.5). They present with variable echogenicity and echotexture depending on the characteristic of the primary tumor.

Not all solid intratesticular lesions are neoplastic [4–7]. Granuloma, focal orchitis, abscess, infarction, fibrous pseudotumor, and hematoma can present as hypoechoic masses at ultrasonographic examination. The patient’s age at presentation is important. Germ cell tumors are prevalent in young, while lymphoma in elderly patients, and some histotypes are much more prevalent in prepuberal boys.

Clinical correlation is vital: many nonneoplastic conditions likely manifest with acute scrotum. One needs to be cautious, however, because also tumors can occasionally manifest with pain. Also history of fever or trauma may suggest a nonneoplastic origin, permitting conservative management. In any case, the ultrasound findings of traumatic and inflammatory changes evolve rapidly; if a nonneoplastic intratesticular pathology is suspected, a short-term follow-up ultrasonographic examination allows differential diagnosis with tumor.

Tumor markers can help in the differential diagnosis between testicular tumors and nonneoplastic lesions. Human chorionic gonadotropin (hCG) is elevated in virtually all patients with choriocarcinoma and with seminomas containing syncytiotrophoblasts. Increased α-fetoprotein is found in yolk sac tumors and in mixed germ cell tumors with yolk sac elements. Sertoli cell tumors may produce excessive estrogen or testosterone, resulting in precocious virilization or feminization. Normal serum tumor markers, however, do not rule out testicular neoplasms.

Although the sensitivity of the newest equipment allows identification of vascular signals in an increasing number of small testicular masses, several lesions less than 1.5 cm may still appear avascular at color Doppler interrogation and cannot be distinguished effectively from nonneoplastic lesions. In our experience virtually, all testicular and extratesticular tumors display vascularization at CEUS [8, 9]. Cystic components in mixed tumors and areas of necrosis or hemorrhage lack contrast enhancement.