A hematoma is a collection of blood outside of blood vessels; when this occurs inside the skull, it is a form of traumatic brain injury (TBI). Both an epidural hematoma (EDH) and a subdural hematoma (SDH) represent serious, life-threatening conditions resulting from head trauma. The primary danger of either condition is the collection of blood forming a mass that presses on the delicate brain tissue. This pressure must be relieved quickly, as the skull cannot expand to accommodate the increasing volume.
Where Epidural and Subdural Bleeding Occurs
The anatomical location of the bleeding dictates the clinical differences between these two conditions. The brain is protected by three layers of membrane called the meninges, which lie directly beneath the skull bone. An epidural hematoma forms in the space situated between the inner surface of the skull bone and the outermost protective membrane, known as the dura mater.
This location is typically a high-pressure environment because the source of bleeding is usually arterial. The middle meningeal artery runs in a groove on the inner surface of the skull and is frequently torn during a traumatic impact, especially one that causes a skull fracture. Since arterial blood is under higher pressure, the hematoma expands rapidly, forcibly peeling the dura mater away from the bone.
A subdural hematoma, in contrast, occurs in a deeper layer, forming between the dura mater and the arachnoid mater, which is the middle membrane. This space is home to the bridging veins that cross from the brain’s surface to drain into larger venous sinuses within the dura. These veins are more fragile than arteries and can be stretched and torn by sudden acceleration or deceleration forces that cause the brain to shift inside the skull.
Because the bleeding comes from these lower-pressure veins, the blood accumulation tends to be slower than an EDH. The venous blood collects in a potential space, allowing it to spread over a wide area and form a crescent shape along the curvature of the brain.
How Symptoms Develop in Each Condition
The high-pressure arterial bleed of an epidural hematoma causes symptoms to progress with alarming speed. A classic presentation for an EDH often involves a brief loss of consciousness immediately after the injury, followed by a period where the patient appears relatively awake and normal, called the “lucid interval”. This temporary lucidity can last for minutes or hours, creating a false sense of security for the patient and observers.
The lucid interval ends when the rapidly expanding hematoma finally overwhelms the brain’s ability to compensate for the rising intracranial pressure. As the blood mass grows, it compresses the brain, leading to a sudden and catastrophic neurological decline, which can include unconsciousness, fixed and dilated pupils, and eventually, brain herniation and death.
Subdural hematomas exhibit a variable timeline for symptom development, depending on the severity of the injury and the patient’s underlying health. An acute SDH results from significant trauma and presents with symptoms within minutes to hours, similar to an EDH, but the underlying brain injury is often more severe. Subacute SDH symptoms may not appear until days to a week after the injury, reflecting a slower rate of bleeding.
A chronic SDH is the slowest-developing form, with symptoms often taking weeks or even months to manifest following a minor or even forgotten head bump. This type is more common in elderly individuals or those on blood thinners, whose brains have shrunk slightly, causing the bridging veins to be stretched and more easily torn. The symptoms of chronic SDH are often subtle, mimicking other conditions like dementia or chronic headaches, which can significantly delay diagnosis and treatment.
Mortality Rates and Recovery Expectations
When comparing the two conditions, the question of which is worse depends on the specific circumstances and the speed of medical intervention. An epidural hematoma represents the more immediate and time-sensitive danger, as the rapid arterial bleeding causes a swift rise in pressure that is quickly fatal if left untreated. If an EDH is recognized promptly and surgically evacuated, the prognosis is often relatively good, with one study showing that nearly 60% of patients achieved a good recovery.
This favorable outcome for timely-treated EDH occurs because the underlying brain tissue is often less damaged than in an SDH. However, if treatment is delayed beyond a couple of hours, the mortality rate for EDH rises dramatically, from approximately 17% to as high as 65%.
Acute subdural hematoma, particularly those resulting from severe trauma, carries a higher overall mortality rate, often ranging from 50% to 90% in severe cases. This higher mortality is due to the force required to tear the bridging veins, which often causes extensive, diffuse injury to the underlying brain tissue, such as contusions and swelling. Even if the hematoma is successfully removed, the patient’s prognosis is worsened by this associated primary brain damage.
Therefore, while an EDH is more immediately life-threatening due to its rapid expansion, an acute SDH is often considered worse in terms of overall outcome and mortality because it is frequently a marker of a more devastating, generalized brain injury. Chronic SDH, due to its slower progression, has a much better prognosis than acute SDH, but it still requires careful diagnosis and monitoring.