A subdural hematoma (SDH) is a serious condition where blood collects inside the skull, specifically between the brain’s surface and the dura mater, the outermost protective membrane. This pooling of blood creates a mass that exerts pressure on delicate brain tissue, leading to increased intracranial pressure. Because the skull is a rigid structure, this pressure buildup can rapidly impair brain function and become life-threatening. Surgical evacuation is often necessary to relieve this compression.
Understanding Subdural Hematoma
The brain is protected by three layers of tissue called the meninges. A subdural hematoma occurs in the space between the dura mater (the tough outer layer) and the arachnoid mater, typically resulting from the tearing of small blood vessels known as bridging veins. These veins cross the subdural space to drain blood from the brain’s surface.
Trauma is the most frequent cause, ranging from severe impacts to minor falls in older adults whose brains may have shrunk, stretching the bridging veins and making them vulnerable to tearing. The speed at which symptoms develop dictates the classification. An acute SDH appears immediately, with symptoms presenting within hours of injury, indicating rapid bleeding.
A subacute hematoma develops more slowly, with symptoms emerging days to a couple of weeks following the injury. In contrast, a chronic SDH is a slower bleed, and symptoms may not manifest until weeks or months after a minor head trauma. As blood collects, the rising intracranial pressure can cause symptoms such as:
- A persistent, severe headache.
- Confusion.
- Weakness or numbness on one side of the body.
- Slurred speech.
- Seizures.
Assessing the Need for Evacuation
The decision for surgical evacuation relies on assessing the hematoma’s characteristics and the patient’s neurological condition. Diagnosis is confirmed using a computed tomography (CT) scan, which provides a rapid image of the brain and the size of the blood collection. A primary radiographic criterion for surgery is the hematoma’s thickness; an acute SDH measuring 10 millimeters or more typically requires immediate intervention.
Another measurement is the degree of midline shift, where pressure pushes the brain structure across the central line of the skull. A shift of 5 millimeters or more indicates significant pressure and necessitates surgical decompression. The patient’s neurological status is quantified using the Glasgow Coma Scale (GCS), which measures eye-opening, verbal response, and motor response.
Surgical evacuation is generally required for patients in a coma, defined as a GCS score of 8 or less, even for smaller hematomas. Intervention is also mandated if a patient’s GCS score drops by two or more points, or if they develop fixed or asymmetrically dilated pupils. If the measured intracranial pressure (ICP) exceeds 20 millimeters of mercury, this sustained elevation is an indication for surgery. For very small, stable hematomas in patients who are awake and alert, conservative management with close observation and serial CT scans may be pursued.
Surgical Evacuation Techniques
The technique chosen depends on the type of SDH (acute or chronic) and the physical state of the collected blood. For acute SDH, where the blood is solid and clotted, a craniotomy is the standard approach. This procedure involves temporarily removing a section of the skull bone (a bone flap) to allow the neurosurgeon full access to the hematoma and underlying bleeding sources. The dura mater is opened, the clot is carefully removed, and bleeding points are controlled before the bone flap is secured back in place.
For chronic or subacute hematomas, where the blood has liquefied, less invasive methods are preferred. Burr hole trephination is the most common technique, involving drilling one or two small holes, usually 12 to 14 millimeters in diameter, into the skull over the hematoma. The dura is opened beneath the holes, allowing the liquefied blood to drain out, often assisted by saline solution.
A third, less invasive option is the twist-drill craniostomy, which uses a specialized drill to create a very small hole, sometimes performed at the patient’s bedside under local anesthesia. A catheter is inserted through this opening to drain the fluid, typically reserved for selected chronic cases. For all drainage techniques, a temporary subdural drain is often left in place for 24 to 48 hours post-operation. This drain ensures complete removal of residual fluid and promotes brain re-expansion, which helps prevent recurrence.
Post-Operative Care and Recovery
Following surgical evacuation, patients are typically transferred to an intensive care unit (ICU) for monitoring of their neurological status and vital signs. Surveillance for signs of re-bleeding or brain swelling is maintained, with follow-up CT scans performed within 24 hours to confirm adequate hematoma removal and brain re-expansion. Pain management is a priority, often involving medications to control common post-operative headaches.
Post-operative complications include the risk of seizures, especially in the first week after surgery, which may necessitate the temporary use of anti-epileptic medications. The hospital stay ranges from several days to a few weeks, depending on the severity of the initial injury and the patient’s rate of recovery. Rehabilitation is often required, involving physical, occupational, and speech therapy to address residual deficits in movement, daily functioning, or communication.
A full recovery trajectory is individualized, depending on the patient’s age and the extent of the initial brain injury. Follow-up appointments and imaging scans are essential to monitor for the long-term risk of subdural hematoma recurrence, a risk elevated with chronic SDH. Patients are advised to gradually resume normal activities, avoiding strenuous effort for several weeks, and may require temporary restrictions, such as not driving, until cleared by their neurosurgeon.