Subdural hematomas typically result from the traumatic rupture of bridging veins that cross the subdural space between the brain surface and the superior sagittal sinus (90% of cases). These injuries are more common in infants, when the brain is not fully developed, and in the elderly, after senile brain atrophy has occurred. Either case results in longer, more fragile bridging veins. In the elderly, alcohol may be involved in up to 50% of cases, while shearing action from shaking (“shaken baby syndrome”) is the likely etiology in infants.

On CT, acute SDHs usually result in a hyperdense, crescent-shaped area that conforms to the outer brain surface, forming in the potential space between the dura and arachnoid. Anemic patients or those in DIC may have a more isodense appearance, making diagnosis more difficult. The appearance and shape of chronic SDHs is much more variable, as they generally become less dense over 1-2 weeks as the tertiary structure of hemoglobin is lost and the clot is metabolized. Highly vascular membranes develop around the hematoma site, which are then vulnerable to rebleeding injury (as may have occurred in this patient).