Subdural hygroma versus atrophy on MR brain scans: "the cortical vein sign".

PURPOSE To determine if the position of the superficial cerebral cortical veins can be used to distinguish subdural hygroma from atrophy on MR brain scans. METHODS Retrospective review of MR scans obtained in cases of extracerebral fluid collections, separating these into two groups, ie, subdural hygroma or atrophy. FINDINGS All cases of atrophy in this study showed cortical veins and their branches traversing widened cerebrospinal fluid spaces over the cerebral convexities. None of the subdural hygroma patients showed this finding. Cortical veins in hygroma patients were seen only at the margin of the displaced cortex, and did not traverse the fluid collections over the cerebral convexities. CONCLUSIONS The authors call the visualization of cortical veins and their branches within fluid collections at the cerebral convexities "the cortical vein sign." They believe this sign to be prima facie evidence of atrophy; its presence rules out the diagnosis of subdural hygroma in the region of interest.