Epidermoid cyst of the testis: An atypical sonographic appearance.

Epidermoid cysts are rare. They represent the most common benign tumor of the testis. The sonographic appearances of testicular epidermoid cysts usually include avascular, mostly lamellated, heterogeneous internal echotexture, with hypoechoic and hyperechoic concentric rings, accounting for the typical onion-ring appearance. On MRI, epidermoid cysts show a low-signal-intensity center, with internal concentric rings of alternating high- and low-signal intensity on T2-weighted images, which correlates with the onion-ring appearance. We report a patient with testicular epidermoid cyst with atypical ultrasound and MRI appearances that led to the erroneous initial diagnosis of "burned-out" tumor.