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Subdural Hematoma

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A subdural hematoma is a pool of blood that forms just under the outer covering of the brain (the dura). The hematoma is not in the brain itself, but sits between the brain and the dura. Subdural hematomas put pressure on the brain below, and can cause symptoms and damage as they compress vital brain structures.

Acute vs Chronic Subdurals
Subdural hematomas are usually caused by head trauma that bursts veins in the subdural space. A severe trauma can cause an acute, life-threatening hematoma to form. Milder trauma can cause a small bleed to start without causing any immediate symptoms, but the resulting pool of blood can eventually create pressure on the brain. (This is known as a chronic subdural hematoma.) Any head injury should be evaluated immediately. A diagnosis of an acute subdural hematoma is a medical emergency that requires immediate evaluation and possible treatment.

Even minor head injuries may sometimes cause enough bleeding to create a small hematoma, which grows slowly and may not cause any immediate symptoms; the potential for developing this kind of chronic subdural hematoma is another reason why all head injuries, regardless of severity, should be evaluated.

A subdural hematoma can also occur spontaneously, especially in infants and the elderly, in those who take blood-thinning medications, in those with a history of alcohol use, and in individuals who have suffered multiple minor head injuries, none of which individually was serious enough to cause the hematoma.

Evaluating and Treating Subdurals
Some small hematomas may be treated with medication, or monitored until they resolve on their own, but larger and symptomatic hematomas often require surgical treatment.

Evaluations of acute and chronic subdural hematomas with CT and MRI are similar. The urgency is dependent upon the patient's neurological status. Thus an initial evaluation should be performed by experts (neurologists and neurosurgeons) in this condition.

Surgery for acute subdural hematomas requires temporarily opening the skull, draining the blood, repairing the injured vessel, then putting the bone back during closure. If the brain is severely swollen, the bone may need to be left out, and just the skin is closed. When swelling subsides, the bone can be replaced. Recovery is dependent upon the severity of the initial injury.

Until recently, most subdural hematomas that needed to be removed surgically required open surgery. Open surgery for chronic subdurals may be done through a small (1 cm) opening in the skull (called a burr hole) or a slightly larger window (about the size of a silver dollar) to drain the blood. Recovery from chronic subdurals is usually complete.

Minimally Invasive Option for Chronic Subdurals
Recent advances described in a paper by Dr. Jared Knopman allow neurosurgeons to treat chronic subdural hematomas using a minimally invasive procedure called middle meningeal embolization. In the embolization procedure, a tiny catheter is threaded up to the arteries feeding the subdural hematoma membrane starting from the femoral artery, accessed by a small needle stick in the groin. Small particles of polyvinyl alcohol are released through the catheter into the middle meningeal artery to shut down the blood supply to the hematoma. This interrupts the blood supply to the hematoma, felt to be involved in the frequent spontaneous re-bleeds observed that account for its growth and development over time. Subsequently, the hematoma can reabsorb on its own and disappear.  (See the abstract of the paper.)

The new minimally invasive approach to treating subdural hematomas is especially helpful in elderly patients, who are most vulnerable to complications when they undergo major open surgery. (Read Dr. Knopman's blog post about this new procedure.)

Subdural hematomas are best treated in major medical centers by experts with advanced training and extensive experience treating cerebrovascular disorders. Dr. Knopman has pioneered the endovascular technique and is the first neurosurgeon in the country to offer it, thus far having treated nearly 150 patients using the new embolization procedure, which spares patients major surgery and prolonged recovery times. (Find out more about this procedure.)

Note that another type of hematoma, epidural hematoma, can form between the dura and the skull, typically when trauma causes the arteries in that space to rupture. The actress Natasha Richardson died of an epidural hematoma after a fall while skiing.  

Reviewed by Philip E. Stieg, PhD, MD
Last reviewed/last updated: April 2021