For evaluation of the perihematomal edema, T2-weighted fluid attenuation inversion recovery sequences (FLAIR) and standard T2-weighted images have been proven to be reliable (Fig. 2) (5,14). The edema volume is calculated by tracking the outer boundaries of the perihematomal edema, multiplying the surface areas on each slice with the slice thickness and then subtracting the hematoma volume from the hematoma plus edema volume. Up to now there has been no clear consensus as to whether the hyperintensity on FLAIR sequences reflects edema caused by blood degradation product-related brain damage or, at least in parts, acute ischemic brain damage (i.e., due to compression of perilesional arteries). Diffusion-weighted images (DWI) and calculation of apparent diffusion coefficient (ADC) maps seem to be helpful for differentiating between perihematomal ischemia and edema since diffusion is reduced in acute ischemia with cytotoxic edema and increased in vasogenic extracellular edema not related to ischemia (19). Perfusion-weighted images (PWI) necessitating the injection of gadolinium-DTPA for calculation of mean transit times may also allow differentiation of ischemia from edema (19). It should be noted that the diffusion and perfusion changes are quite subtle and cannot be directly visualized. Therefore, measurement of quantitative values in predefined regions of interest (ROI) is necessary to detect these differences.

Only few groups have proposed imaging of the hematoma with computerized tomography (CT). Shi and coworkers used CT scanning in piglets (20). The comparatively small volume of the pig brain in relation to the thick bone and the inability to visualize the edema properly are the major restrictions of CT scanning.