MRI Distinguishes Seminomatous From Nonseminomatous Testicular Neoplasms

The objective of a recent study was to assess the ability of MRI for preoperatively characterizing the histologic type of testicular tumor, and to distinguish between seminomatous and nonseminomatous testicular neoplasms.
The study has concluded that MRI can provide information allowing for reliable preoperative characterization of testicular neoplasms, particularly differentiating between seminomatous and nonseminomatous tumors.

Participants
In this retrospective analysis, 21 patients with germ cell testicular tumors proven at histology who were referred for evaluation of a painless scrotal mass participated in the study.

Methodology
Ultrasound and MRI were performed. MRI examinations were performed with a 1.5-Tesla system. Imaging sequences included axial T1-weighted, as well as axial, coronal, and sagittal T2-weighted images.
Axial T1-weighted images were also performed following administration of IV gadolinium contrast. MRI images were interpreted by 2 radiologists experienced in MRI of the scrotum. Lesion detection and characterization were performed.
Signal intensity of the mass lesion was compared with that of the normal testicular parenchyma. Absence or presence of the following findings was recorded:

• lesion homogeneity,
• tumor capsule,
• necrosis,
• hemorrhage,
• fat,
• fibrovascular septa,
• and pattern of contrast enhancement.

Findings were compiled to try to differentiate between seminomatous and nonseminomatous testicular neoplasms. Based on their cellular uniformity and nodular histologic characteristics, seminomas are expected to be hypointense on T2-weighted images and contain fibrovascular septa that enhance to a greater degree compared to the tumor itself. In contradistinction, nonseminomatous germ cell neoplasms are expected to be heterogeneous with a combination of hemorrhage, necrosis, or fat.

Results
There were 10 seminomas and 11 nonseminomatous germ cell neoplasms. Nonseminomatous lesions included teratocarcinoma, embryonal carcinoma, teratoma, choriocarcinoma, and yolk sac tumor. MRI findings were concordant with histological diagnosis in 19 of 21 cases. Nine of 10 seminomas were correctly characterized by MRI prior to surgery. Seminomas were predominantly hypointense on T2-weighted images and contained fibrovascular septa that enhanced to a greater degree than the tumor tissue.

A minority contained areas of necrosis and/or hemorrhage. The tenth lesion was homogeneously hypointense on T2-weighted images and preoperatively characterized as a seminoma, which subsequently proved to be an embryonal carcinoma.
MRI correctly characterized 10 of 11 lesions as nonseminomatous germ cell neoplasms. These lesions were heterogeneous on T2-weighted images and demonstrated heterogeneous enhancement.
A few of these lesions had areas of necrosis, hemorrhage, or fat. The eleventh lesion was markedly heterogeneous on T2-weighted images with areas of necrosis and heterogeneous enhancement and preoperatively characterized as nonseminomatous germ cell neoplasm, which subsequently proved to be an anaplastic seminoma.
Five of 9 seminomas and 9 of 10 nonseminomatous neoplasms had a hypointense halo that corresponded to a fibrous capsule at histology.

Reviewer’s Comments
These Results are useful in demonstrating the credible possibility of distinguishing between seminomatous and nonseminomatous germ cell testicular tumors at MRI examination.

Author: :
John C. Sabatino, MD, MSD

Reference: :
Tsili AC, Tsampoulas C, et al. MRI in the Histologic Characterization of Testicular Neoplasms. AJR; 2007; 189 (December): W331-W337