The Full form of SDH is Subdural Hematoma. SDH is a common neurosurgical disorder that often requires surgical intervention. It is a type of intracranial hemorrhage that occurs beneath the dura (essentially, a collection of blood over the surface of the brain) and may be associated with other brain injuries. In simple words, a SDH is a collection of clotting blood that forms in the subdural space. This may be an acute SDH, a subacute SDH (this phase begins 3-7 days after the initial injury) or a chronic SDH (this phase begins 2-3 weeks after the initial injury). There is also a simple SDH (when there is no associated parenchymal injury) or a complicated SDH (when there is associated underlying parenchymal injury, such as contusion). An acute SDH is usually caused either by bleeding from a damaged cortical artery or tearing of bridging veins from the cortex to one of the draining venous sinuses – typically occurring when bridging veins are sheared during rapid acceleration-deceleration of the head. Blunt head trauma is the usual mechanism of injury but spontaneous SDH can arise as a consequence of clotting disorder, arteriovenous malformations/aneurysms or other conditions.