Subdural Hematoma

Accumulation of blood between the dura mater and the arachnoid, usually from bleeding of the bridging veins.

Subdural hematomas develop when blunt head trauma causes brain motion within the skull, shearing off the bridging veins between the brain's surface and adjacent dural venous sinuses. The blood leaks and accumulates slowly. The resulting subdural hematoma may be absorbed spontaneously or, after about 2 weeks, may become encapsulated with a liquefied center. The vascular outer membrane of the hematoma may continue to bleed, causing the center to enlarge.

Etiology

Subdural hematomas may be acute (due to severe head trauma) or chronic (usually due to minor trauma). Chronic subdural hematomas typically occur in elderly persons taking anticoagulants or in alcoholics who have some degree of brain atrophy. Other causes include falls, bleeding disorders, and, occasionally, lumbar puncture. Some subdural hematomas occur without previous trauma. Some patients forget a fall or other trauma or consider it too inconsequential to mention. Often, a fall causes retrograde amnesia, and patients may not be fully aware of the injury.

Symptoms and Signs

The most common findings are headache, decreased alertness, and abnormalities of hemispheric function. Headache, usually ipsilateral to the hematoma, may worsen at night. Drowsiness and decreased alertness are due to increased intracranial pressure. Slight weakness, hyperreflexia, and Babinski's sign in the contralateral limbs are common. Patients with a left-sided hematoma may have slight aphasia, and patients with a right-sided hematoma may have right-sided spatial neglect. Usually, neurologic abnormalities are mild. Seizures may occur, probably indicating contusion of underlying brain tissue. As the hematoma enlarges, headache worsens and the level of consciousness often decreases. An ipsilateral Babinski's sign and ipsilateral 3rd-nerve paresis may develop, indicating midbrain compression.

In alcoholic patients with brain atrophy, bleeding often persists, causing headaches, behavioral changes, an altered level of consciousness, and focal neurologic deficits (eg, hemiparesis).

Diagnosis

Elderly patients with behavioral and neurologic abnormalities (including dementia) should be screened for hematomas, a treatable cause of such abnormalities.

For patients with a history of head trauma, the diagnosis is usually obvious. Chronic subdural hematomas, whose symptoms develop insidiously, must be distinguished from vascular dementia, brain tumor, and brain abscess, especially if patients provide no history of trauma. Subdural hematomas can be distinguished from brain infarcts and intracranial hematomas, whose symptoms and signs usually begin more acutely and include more severe focal deficits.

Neuroimaging is necessary to confirm the diagnosis. On a CT scan, an acute subdural hematoma appears as a sickle-shaped, hyperdense lesion over the outer surface of the brain, lying against the inner surface of the skull and dura. A subacute (lasting 7 to 14 days) subdural hematoma appears isodense in relation to the brain, making diagnosis difficult. During the acute period, a T1-weighted MRI can help because it can detect a high-signal-intensity lesion in the subdural space. A chronic subdural hematoma appears hypodense on CT scans.

Prognosis and Treatment

Patients with an acute subdural hematoma have a poor prognosis. The mortality rate for patients treated for an acute subdural hematoma is about 50%. If a chronic subdural hematoma is recognized and treated, the prognosis is good and is related primarily to the degree of associated brain injury.

Subdural hematomas are surgically evacuated. However, small ones may heal spontaneously without medical treatment. In elderly patients and patients with brain atrophy, reexpansion of the compressed brain may be delayed. Because subdural bleeding may recur, a drain must be left in for several days and the patient must be monitored closely for bleeding.