A subdural hematoma is an abnormal collection of blood that layers between the fibrous covering of the brain known as the dura and the brain itself. Subdural hematomas occur when veins that bridge the gap between the dura and brain tear.
Most commonly bridging veins tear after trauma to the head. Older individuals with more brain atrophy are at higher risk because their bridging veins are under tension as they span the atrophic gap between the dura and the underlying brain. Although subdural hematomas may also occur in younger patients with significant head trauma.
There are three different “flavors” of subdural hematoma: acute, subacute, and chronic. They are distinguished from one another based on CT imaging characteristics. The imaging characteristics give the treating physician an idea of how “old” the blood is (ie: how long has the blood been in the subdural space). An acute subdural hematoma indicates active bleeding that has occurred within a few hours of the CT scan. A subacute subdural indicates that the bleeding occurred at least 3 days to 2 weeks prior to the CT scan. And finally a chronic subdural is one in which the bleeding occurred greater than 2 weeks prior to the scan.
CT scan imaging characteristics help distinguish the different types of subdural hematoma. An acute subdural hematoma is usually "hyperdense" on CT scan, which means that the blood appears lighter (whiter) in color than the adjacent brain tissue. Subacute subdural hematomas are "isodense" meaning that they take on a grayish color similar to the underlying brain; chronic subdural hematomas are “hypodense”, which means that the blood appears darker (blacker) than the underlying brain tissue.
Occasionally a phenomenon known as "acute on chronic" subdural hematoma occurs, which indicates that new bleeding has occurred into an area of older blood.
Signs and symptoms vary depending on the location, acuity and severity of the bleed. Subdural hematomas cause symptoms by putting pressure on the underlying brain tissue. Patients may present with weakness (either overt or subtle) if the blood is pushing on the motor cortex. The increased pressure inside the patient’s head may cause headache, nausea, and vomiting. Large acute subdural hematomas can present with coma and brain death as they force brain tissue to herniate down into the foramen magnum at the base of the skull.
Subdural hematomas are readily diagnosed with CT scans of the head. MRI can also detect subdural hematomas, but takes longer and is not as useful in patient's who are exhibiting acute neurological deterioration.
Treatment is based on symptoms and the size of the subdural hematoma. Many patients have small subdurals that require no intervention. However, if the blood is greater than 15mm, causing more than 5mm of midline shift, or the patient is symptomatic most neurosurgeons recommend surgical evacuation of the blood.
Surgery consists of either burr holes or craniotomy. Burr holes (ie: two holes placed several inches apart) are most successful with subacute and chronic subdural hematomas because the blood is more liquefied and can be “washed” out with copious irrigation. Subacute blood is usually thick and gelatinous because it is attempting to form a clot. As a result, a craniotomy (ie: the removal of a larger piece of skull) is necessary to remove the blood.
A subdural hematoma is blood that sits on top of the brain just below the covering of the brain known as the dura mater. Subdurals come in three flavors: acute, subacute, and chronic. The type of subdural is dependent on how long the blood has been in the subdural space. Symptoms range from none to coma and death. Treatment is based on the size of the subdural as well as whether or not symptoms are present. Surgery with either burr holes or craniotomy is
- Traumatic brain injury
(1) Baehr M, Frotscher M. Duus' Topical Diagnosis in Neurology: Anatomy, Physiology, Signs, Symptoms. Fourth Edition. Stuttgart: Thieme, 2005.
(2) Kumar V, Abbas AK, Fausto N. Robbins and Cotran Pathologic Basis of Disease. Seventh Edition. Philadelphia: Elsevier Saunders, 2004.
(3) Greenberg MS. Handbook of Neurosurgery. Sixth Edition. New York: Thieme, 2006. Chapter 25.
(4) Ducruet AF, Grobelny BT, Zacharia BE, et al. The surgical management of chronic subdural hematoma. Neurosurg Rev. 2012 Apr;35(2):155-69; discussion 169. Epub 2011 Sep 10.