Sedimentation level in chronic subdural hematoma visible on computerized tomography.

A clear interface dividing subdural hematoma into an upper hypodense and a lower hyperdense part was seen on computerized tomography (CT) scan in seven of 140 patients with chronic subdural hematoma. All except one of the seven patients had a definite history of head trauma more than 1 month before they developed acute disturbances of consciousness and pronounced hemiparesis. Consequently, they remained bed-ridden until they underwent drainage of the subdural hematoma. This group was compared to seven chronic subdural hematoma patients with mild clinical manifestations who were selected and intentionally confined to bed for a period before CT examination and craniotomy. The CT scans in this latter group did not show the clear interface in the subdural hematoma seen in the first group. Based on this study, it is hypothesized that this sedimentation level occurred as a result of rebleeding into a chronic hematoma that was sufficiently old to result in its contents being homogenous prior to the rebleed. In cases of rebleeding, a sufficient period of bed confinement in the brow-up position before CT examination allows development of a gravitational sedimentation in the hematoma. This clear level of sedimentation is seen in only a small portion of patients, but this finding may be specific for a significant amount of rebleeding and may herald acute deterioration.