A subdural hematoma (SDH) is a serious form of traumatic brain injury involving internal bleeding within the protective layers surrounding the brain. This condition occurs when blood collects, forming a clot that exerts pressure on brain tissue. Recognizing this medical emergency is important because signs can appear immediately after an injury or be significantly delayed, leading to complications if not treated promptly.
Defining the Subdural Hematoma
The brain is protected by three layers of tissue, collectively known as the meninges, which sit just inside the skull. The outermost layer is the tough, fibrous dura mater, and the layer beneath it is the arachnoid mater. A subdural hematoma refers to a collection of blood that pools in the space between these two layers. This blood clot presses inward, increasing pressure within the skull that can displace or damage the brain.
Hematomas are classified based on the time it takes for symptoms to appear after the initial injury. An Acute SDH is the most life-threatening form, where signs develop rapidly, typically within minutes to hours of severe head trauma. The rapid accumulation of blood causes a swift increase in intracranial pressure.
A Subacute SDH presents more slowly, with symptoms emerging days to a few weeks following the injury. The Chronic SDH is often seen in older adults, where bleeding is slow and subtle. Symptoms may not become apparent until weeks or months after a minor incident, making the diagnosis more challenging.
Causes and Risk Factors
The underlying mechanism for a subdural hematoma is usually the tearing of small blood vessels called bridging veins. These veins cross the subdural space to drain blood from the brain’s surface and are vulnerable to shearing forces. Rapid acceleration or deceleration of the head can stretch and rupture these veins, which commonly occurs in events like falls, car accidents, or violent shaking.
Several factors increase susceptibility to this type of injury, even from minor trauma. Advanced age is a significant risk factor because the brain naturally shrinks (atrophy) over time. This atrophy stretches the bridging veins and makes them more fragile. This means even an insignificant bump to the head can cause a slow leak that develops into a chronic hematoma.
The use of blood-thinning medications, such as anticoagulants and antiplatelet drugs, raises the risk by inhibiting the body’s ability to form clots, leading to more severe bleeding. Chronic alcohol use also increases risk due to associated brain atrophy and liver damage that impairs the blood clotting process. Infants are vulnerable, with subdural hematomas sometimes resulting from abusive head trauma, commonly referred to as shaken baby syndrome.
Recognizing the Signs and Symptoms
The presentation of a subdural hematoma depends on its classification, particularly the difference between acute and chronic types. Patients with an Acute SDH typically experience a rapid decline in neurological function due to the quick increase in pressure on the brain. Common signs include severe headache, confusion, sudden loss of consciousness, weakness or numbness on one side of the body, and seizures.
The signs of a Chronic SDH are more subtle and can fluctuate over time, often leading to misdiagnosis. These symptoms develop gradually and may mimic other conditions, especially in older patients. Common manifestations include a mild but persistent headache, memory issues, difficulty maintaining balance or walking, and personality changes.
The slow nature of chronic symptoms means a patient might not connect their current difficulties to a minor fall that occurred weeks or months earlier. Any new or worsening neurological symptom, such as slurred speech, dizziness, or confusion, should prompt immediate medical evaluation, especially with a history of recent head trauma, regardless of how minor it seemed.
Medical Diagnosis and Treatment Protocols
When a subdural hematoma is suspected, neuroimaging is the primary method for confirming the diagnosis. A Computed Tomography (CT) scan is typically the first choice because it is fast and effectively visualizes fresh blood collections. Magnetic Resonance Imaging (MRI) may also be used, particularly for chronic or subacute cases, as it provides greater detail of the brain’s soft tissues and helps distinguish between blood of different ages.
Treatment protocols vary based on the size of the hematoma, its classification, and the patient’s neurological status. Small, stable hematomas not causing severe symptoms may be managed through careful observation and supportive medical care. This approach involves frequent neurological checks and repeat imaging to ensure the clot is not growing.
For larger or rapidly expanding hematomas, surgical intervention is necessary to relieve pressure. The most common procedure for an Acute SDH is a Craniotomy, where a section of the skull is temporarily removed to fully access and evacuate the solid blood clot. For Chronic SDH, which often contains liquefied blood, a less invasive technique called Burr Hole Trephination is frequently used. This involves drilling small holes into the skull to insert a drain, allowing the accumulated fluid to be drained and relieve the intracranial pressure.