Specific Imaging Findings

Acute subdural hematoma (SDH) is usually a hyperdense mass located along the brain surface on CT. It may displace and compress the adjacent brain, but it does not extend into the cortical sulci. SDH has a characteristic concave interface with the underlying parenchyma, although it may also present with a lenticular shape, particularly in the hyperacute setting. Hyperacute SDH can also be of mixed density (due to active bleeding, unclotted blood and admixture of CSF), sometimes with a characteristic “swirling” pattern. SDH can spread along an entire hemisphere as it is located underneath the dura and not limited by dural attachments at the cranial sutures; however, it may not cross the falx and the tentorium. MRI reveals small SDHs that may be inconspicuous on CT. The evolution of MRI signal characteristics of SDHs differs from the intraparenchymal hematomas and they are most commonly bright on all sequences, including DWI, with a frequent relative hypointensity on T2* images. On post-contrast images, SDH shows peripheral enhancement of the dura, which may also be thickened, especially with chronic SDH. Chronic SDH may also show calcification of the thickened dura, best seen on CT.

Pertinent Clinical Information

vehicle collisions, falls, and non-accidental trauma; they may also occur spontaneously (as with coagulopathies). SDH may resolve or develop into chronic collections. Re-bleeding can occur within an existing SDH following only minor injury, often not even noticed by the patient. Surgical management of an acute SDH is based on the patient’s clinical status, size of the collection, and associated mass affect; rapid treatment is the goal as the chance of survival falls off steeply if elevated intracranial pressure is not relieved within the first 60 min, known as the “golden hour”.