Anatomically, there are three distinct potential spaces between the skull and the surface of the brain where hematomas may accumulate: the epidural space is between the skull and the dura, the subdural space is between the dura and the arachnoid, and the subarachnoid space is between the arachnoid and the pia (which lines the cortical surface of the brain). Subdural hematomas (SDH) typically result from venous bleeding from torn bridging veins that traverse the potential space beneath the dura. SDHs can be subdivided into two groups: acute SDH and chronic SDH; the etiologies and the treatment options may vary between these two types.

Acute SDH

Etiology

Acute subdural hematomas most often occur soon after significant head trauma. Patients with acute traumatic SDH may also have other intracranial pathologic lesions contributing further to elevated intracranial pressure. Potential coexisting intracranial pathologies include: cerebral contusions, intraparenchymal hemorrhages, epidural hematomas, and/or subarachnoid hemorrhages.

Unlike epidural hematomas (which arise from brisk arterial bleeding), acute subdural hematomas may form over several hours after the injury from slow venous bleeding in the subdural space. Consequently, patients who accumulate large acute subdural hematomas may have a lucid interval of up to a few hours before becoming progressively confused or (in some cases) comatose.

Acute SDHs can also occur without any history of significant head trauma. For instance, patients with coagulopathies and/or vascular disorders are more prone to develop hematomas spontaneously or with even the slightest trauma to the head.