MRI in the histologic characterization of testicular neoplasms

OBJECTIVE. The purpose of our study was to investigate the potential role of MRI in the preoperative characterization of the histologic type of testicular tumors and, more specifically, to differentiate seminomatous from nonseminomatous testicular neoplasms. MATERIALS AND METHODS. Twenty-one patients with histologically proven germ cell testicular tumors underwent MRI of the scrotum on a 1.5-T unit. T2- and T1-weighted sequences before and after IV administration of gadolinium chelate were performed. MRI studies were retrospectively reviewed by two radiologists and findings were correlated with the histopathologic diagnosis. An attempt was made to differentiate seminomatous from nonseminomatous testicular tumors on the basis of signal intensity and homogeneity of the lesions, presence of fibrovascular septa, tumor encapsulation, and patterns of contrast enhancement. Interobserver agreement was assessed using weighted kappa statistics. RESULTS. MRI findings correctly characterized 19 (91%) of 21 testicular neoplasms (nine seminomatous and 10 nonseminomatous testicular tumors), with excellent interobserver agreement. The presence of an intratesticular lesion of predominantly low signal intensity on T2-weighted images, with septa enhancing more than tumor tissue after contrast material administration, was more suggestive for the diagnosis of a seminoma. Tumors that were markedly heterogeneous both on unenhanced and contrast-enhanced images were indicative of a nonseminomatous neoplasm. CONCLUSION. Our study shows that MRI provides a credible preoperative differentiation of seminomatous from nonseminomatous testicular tumors, with excellent interobserver agreement.