Chronic Subdural Hematomas: Pathophysiological Studies with MR Imaging and SEP

Abstract

Comparative evaluations of the MR findings, clinical symptoms, and hematoma fluid contents of 19 chronic subdural hematomas(CSHs) in 16 patients were performed to clarify the etiology of the development of CSH. CSHs were classified into four groups according to the MR findings. Hematomas showed iso-or hypointense on T1-weighted(T1-W) images and proton density-Weighted(D-W) images and hypointense on T2-weighted(T2-W) images in 6 CSHs (group A). They were hyperintense on T1-W and D-W images and hypointense on T2-W images in group B (10 CSHs) and hyperintense on T1-W, D-W, and T2-W images in 2 CSHs (group C). In the remaining CSH (group D), the hematoma showed mildly hypointense on T1-W images, isointense on D-W images, and hyperintense on T2-W images (group D). The intervals between the onset of symptoms and MR examinations were less than 5 days in 5 of 6 CSHs of group A, 4–16 days in all but one CSHs of group B (the exceptional one being an incidental case), 22 and 32 days in group C, and 46 days in group D. RBC counts, Hb, and the Hct of the hematoma fluid were also the highest in group A and the lowest in group D. This finding indicates that large amount of rebleeding took place as neurological symptoms developed and that rebleeding into a hematoma cavity was also responsible for the enlargement of CSH. The central conduction times (CCTs) of somatosensory evoked potentials(SEPs) were examined, because not only the motor pathway but also the sensory pathway should be affected by the extraaxial mass. CCTs were examined in 8 of 14 CSHs with motor weakness, however no case showed an abnormality of the sensory pathway. This suggests that the motor function was more vulnerable to extraaxial compression than the sensory pathway. Further studies are indicated for the evaluation of these mechanisms.