Diffusion-Weighted Imaging Characteristics of Primary Central Nervous System Germinoma with Histopathologic Correlation:

Rationale and Objectives

The aim of this study was to quantify, using diffusion-weighted magnetic resonance imaging, the microscopic rate of water diffusion in pure germinoma and to determine whether or not the apparent diffusion coefficient (ADC) values correlated with the different histologic components.

Materials and Methods

A retrospective analysis of echoplanar diffusion-weighted magnetic resonance images was conducted on 10 patients with 11 germinoma lesions. All images were obtained using 1.5-T magnets with a b value of 1000 s/mm². Regions of interest were drawn separately within the solid and the cystic or necrotic components of each germinoma, as well as within the normal gray and white matter of the respective cases, to calculate ADCs. The diffusion characteristics of the germinomas were assessed using mean and normalized ADC values. Histologic samples from all cases were blindly reviewed and then correlated with the ADC values.

Results

Data are expressed as mean ± standard error. Evaluation of the solid components revealed that 36% of germinomas (4 of 11) had predominantly restricted diffusion (ADC_solid, 694.71×10⁻⁶±74.54×10⁻⁶ s/mm²; ADC ratio, 0.84±0.07) compared to normal brain. The majority (55% [6 of 11]) had normal diffusion (ADC_solid, 947.64×10⁻⁶±54.38×10⁻⁶ s/mm²; ADC ratio, 1.14±0.10). Only 9% (1 of 11) had increased diffusion (ADC_solid, 1172.30×10⁻⁶±48.52×10⁻⁶ s/mm²; ADC ratio, 1.67±0.16). The cystic and necrotic components had a mean ADC ratio of 2.55±0.25. There was no significant correlation between the histologic components and the ADC values of germinomas.

Conclusions

The vast majority of germinomas demonstrated predominantly restricted (36%) or normal (55%) diffusion. The histologic components were not correlated with the ADC values.

Key Words: Germinoma, germ cell tumor, diffusion, central nervous system, magnetic resonance (MR), mean diffusivity