Evaluation of solid lesions affecting masticator space with diffusion-weighted MR imaging.

The aim of this study was to evaluate the value of diffusion-weighted magnetic resonance (MR) imaging in differentiating various masticator-space solid lesions.Before surgery and/or pathologic verification, diffusion-weighted echo-planar MR imaging was performed on 78 subjects who had lesions in their masticator spaces. Based on their pathologic outcomes, lesions were classified into 3 groups: group 1: benign tumors and tumor-like lesions (23 cases); group 2: inflammatory diseases (14 cases); and group 3: malignant tumors (41 cases). Mean apparent diffusion coefficients (ADCs) were calculated from diffusion-weighted MR images that were obtained with a b factor of 0 and 1,000 s/mm(2). Differences between groups and lesion types were statistically compared with the Kruskal-Wallis and Mann-Whitney U tests.The ADCs were significantly different (P = .0001) among the 3 groups, between group 1 (1.52 +/- 0.29 [SD] x 10(-3) mm(2)/s) and group 2 (1.01 +/- 0.31 x 10(-3) mm(2)/s), and between group 1 and group 3 (1.11 +/- 0.29 x 10(-3) mm(2)/s). There was no statistically significant difference (P = .31) in ADCs between group 2 and group 3. In addition, there were significant differences between osteosarcomas (1.40 +/- 0.28 x 10(-3) mm(2)/s) and inflammatory diseases (P = .038) and between osteosarcomas and carcinomas (1.11 +/- 0.26 x 10(-3) mm(2)/s; P = .035).Diffusion-weighted MR imaging may be valuable in differentiating between benign solid lesions and malignant tumors in the masticator space. Inflammatory lesions cannot, however, be separated from most malignant tumors, except for osteosarcomas.