A subdural hematoma (SDH) is a serious form of bleeding on the surface of the brain, typically resulting from a head injury. This condition involves a collection of blood pooling between two protective layers surrounding the brain, creating a mass that puts pressure on the underlying tissue. Because the skull is a rigid structure, this expanding blood accumulation quickly elevates pressure inside the head. This can cause significant neurological damage or death, making SDH a medical emergency requiring immediate assessment and intervention.
The Mechanics of a Subdural Hematoma
The brain is protected by three layers of membranes called the meninges. An SDH forms in the subdural space, which lies between the outermost layer (dura mater) and the arachnoid mater. The bleeding source is most commonly the bridging veins, small blood vessels that traverse this space to drain blood from the brain’s surface. When the head undergoes sudden, violent movement, such as rapid acceleration or deceleration, the brain shifts within the skull. This motion stretches and tears the bridging veins, causing blood to leak into the subdural space.
Since this bleeding is typically venous, it is under less pressure and accumulates more slowly than arterial bleeds. The rate of accumulation determines the injury classification, which is based on the time elapsed since the injury.
Types of Subdural Hematoma
An acute SDH involves symptoms appearing within 72 hours of trauma, posing the most immediate threat due to rapid pressure increase. A subacute SDH presents between three days and three weeks after the event. A chronic SDH is present for three weeks or longer, often resulting from a minor, unnoticed injury.
Common Causes and Vulnerable Populations
The primary cause of a subdural hematoma is head trauma, ranging from high-impact injuries like car accidents and falls to minor bumps. The force causes the brain to shift, straining and tearing the bridging veins. While severe trauma typically causes acute SDH, minimal force can lead to chronic SDH, especially in susceptible individuals.
Vulnerable Populations
The elderly population is highly vulnerable due to age-related brain atrophy. As the brain shrinks, the bridging veins are stretched, making them susceptible to tearing from slight head movements or falls. Individuals taking anticoagulant or antiplatelet medications (blood thinners) also face higher risk because their blood does not clot efficiently. This allows a small tear to result in a larger, more persistent bleed.
In infants, SDH is a frequent finding in cases of abusive head trauma, often called shaken baby syndrome. Violent shaking causes the infant’s head to move rapidly, tearing the bridging veins. Other risk factors include chronic alcohol use, which contributes to brain atrophy, and conditions that affect blood clotting, such as hemophilia.
Recognizing the Warning Signs
The symptoms of a subdural hematoma vary widely based on the size and speed of the bleed. In acute cases, signs appear rapidly and include sudden, severe headache, confusion, and slurred speech. Other neurological deficits quickly follow, such as weakness or numbness on one side of the body, vision changes, and nausea or vomiting.
As pressure increases, more severe symptoms manifest, including seizures, loss of consciousness, and drowsiness. Chronic subdural hematomas often have subtle symptoms that progress gradually over weeks or months. These slower-developing signs, such as fluctuating low-grade headaches, memory loss, and changes in personality, can mimic conditions like dementia, making diagnosis challenging. Any new or worsening neurological symptom following a head injury warrants immediate medical evaluation.
Medical Assessment and Confirmation
When a subdural hematoma is suspected, medical professionals perform a thorough neurological examination to assess cognitive function, motor skills, and reflexes. This initial assessment determines the severity of the neurological deficit and the urgency of the situation. Definitive diagnosis relies on medical imaging, which provides a detailed view of the brain.
The standard and most rapid imaging tool is a Computed Tomography (CT) scan, typically the first step in an emergency setting. A CT scan quickly detects the presence and size of the blood collection. The blood’s appearance on the CT helps determine the hematoma’s age: acute blood appears bright white (hyperdense), while chronic blood appears dark (hypodense). Magnetic Resonance Imaging (MRI) is used when the CT scan is inconclusive, especially for smaller, chronic, or isodense hematomas where blood density is similar to brain tissue.
Treatment Approaches and Recovery
Treatment for a subdural hematoma depends on the hematoma’s size, development speed, and the patient’s symptoms. Small, chronic, and asymptomatic SDHs are managed conservatively with careful observation and repeated imaging. In these cases, the body may naturally reabsorb the blood collection over time, reducing the need for an invasive procedure.
For larger or symptomatic hematomas, especially acute ones causing significant pressure, surgical intervention is necessary to evacuate the blood.
Burr Hole Trephination
This common procedure involves drilling one or two small holes into the skull over the hematoma. A catheter is inserted through the holes to drain the liquid blood and relieve pressure on the brain. This technique is frequently used for chronic SDHs.
Craniotomy
A Craniotomy is a more extensive surgical option reserved for large, solid, or rapidly expanding hematomas, typically acute SDHs. This procedure requires temporarily removing a larger section of the skull, called a bone flap, to allow the neurosurgeon access to remove the blood clot and control active bleeding. Following treatment, recovery may involve intensive rehabilitation.