Diffusion-weighted MR imaging in brain abscess

We illustrate the high signal intensity of brain abscess on echo-planar diffusion-weighted MR imaging (DWI). Five consecutive patients (mean age 42 years, 4 men and I woman) with proven brain abscess were evaluated with DWI. All the DWIs were performed on a 1.5 T system, using single shot spin-echo echo-planar imaging technique with b value of 1000 s/mm(2). Diffusion gradients were applied in three directions (x, y, z) simultaneously. In all patients, the signal intensity of abscess content was evaluated qualitatively and quantitatively. In the quantitative study, the signal intensity was measured in the central abscess content, surrounding edema, the normal white matter, and the lateral ventricle for the calculation of % contrast of abscess/edema, abscess/normal white matter, and the abscess/lateral ventricle. On the visual inspection all the abscess contents showed very bright high signal intensity, whereas surrounding edema revealed nearly isointensity with the normal white matter on DWIs. The signal intensity of abscess content ranged from 233 to 571 (mean 399), whereas that of surrounding edema ranged from 80 to 144 (mean 105), the normal white matter 82 to 115 (mean 99), and the lateral ventricle II to 23 (mean 16). Mean % contrasts of abscess/edema, abscess/normal white matter and the abscess/lateral ventricle were approximately 380%, 400%, and 2,400 %, respectively. Abscess content revealed bright signal intensity on DWI, presumably due to high viscosity The DWI may be used as an adjuvant method in differentiating brain abscess from the cystic or necrotic tumors.