An epidural hematoma is a collection of blood that forms between the skull and the tough outer membrane covering the brain, called the dura mater. It typically results from a head injury that ruptures an artery running along the inside of the skull, causing blood to pool rapidly in a space where blood doesn’t normally exist. Because the bleeding is arterial and under pressure, an epidural hematoma can become life-threatening within hours, making it one of the most time-sensitive emergencies in neurosurgery.
What Causes the Bleeding
The most common cause is a rupture of the middle meningeal artery, a blood vessel that runs between the skull and the dura. A blow to the side of the head, often at the temple where the skull is thinnest, can fracture the bone and tear this artery. Between 85% and 90% of epidural hematomas are associated with a skull fracture. Because arterial blood is under higher pressure than venous blood, it forces the dura away from the skull and creates a rapidly expanding pocket of blood that compresses the brain beneath it.
Common scenarios include falls, car accidents, sports injuries, and assaults. The injury doesn’t always have to be dramatic. A relatively modest impact to the right spot can fracture the thin temporal bone and set the process in motion.
The “Lucid Interval” and Other Symptoms
Epidural hematomas are known for a distinctive and dangerous pattern: a person loses consciousness at the moment of impact, wakes up and appears fine for a stretch of time, then deteriorates rapidly as the blood collection grows. This window of apparent normalcy is called the lucid interval, and it occurs in roughly 10% to 33% of cases. It’s dangerous precisely because it can fool people into thinking the worst has passed.
Not everyone follows this textbook pattern. Some people never lose consciousness initially. Others remain unconscious from the start. The key warning signs as the hematoma expands include worsening headache, vomiting, confusion, drowsiness that deepens into unresponsiveness, and weakness on one side of the body. A pupil that becomes fixed and dilated on the side of the injury is a late and ominous sign that the brain is being pushed out of position.
How It Looks on a CT Scan
A CT scan of the head is the primary tool for diagnosis, and the appearance is distinctive. An epidural hematoma shows up as a bright, lens-shaped (biconvex) collection pressed against the inner surface of the skull. This shape is a direct result of anatomy: because the dura is normally tightly attached to the skull at the suture lines where skull bones meet, the blood can’t spread freely along the surface. It stays contained in one area, bulging inward like a convex lens.
This shape is one of the clearest ways to distinguish an epidural hematoma from a subdural hematoma, which forms on the other side of the dura, between the membrane and the brain itself. Subdural hematomas spread more freely across the brain’s surface and appear as crescent-shaped collections on imaging.
Epidural vs. Subdural Hematomas
These two types of bleeding around the brain are often confused, but they differ in important ways:
- Location: Epidural hematomas sit between the skull and the dura. Subdural hematomas are deeper, forming between the dura and the brain’s surface.
- Bleeding source: Epidural hematomas usually involve a torn artery, which bleeds fast and under pressure. Subdural hematomas typically come from torn veins, which bleed more slowly.
- Speed of onset: Epidural hematomas tend to progress quickly, often within hours. Subdural hematomas can be acute but are also commonly chronic, developing over days or weeks, particularly in older adults.
- Shape on CT: Epidural hematomas appear biconvex (lens-shaped). Subdural hematomas appear crescent-shaped and can spread across a larger area of the brain’s surface.
When Surgery Is Needed
Brain Trauma Foundation guidelines set clear thresholds. Any epidural hematoma larger than 30 cubic centimeters should be surgically evacuated regardless of how alert the person is. The standard surgical approach involves removing a section of skull bone to drain the blood and relieve pressure on the brain, then controlling the source of bleeding.
Smaller hematomas can sometimes be managed without surgery, but only under strict conditions: the blood collection must be less than 15 millimeters thick with less than 5 millimeters of midline brain shift, the person must have a Glasgow Coma Scale score above 8 (meaning they’re not deeply unconscious), and there can be no signs that the brain is being pushed downward. Even then, this requires frequent neurological checks, repeat CT scans, and a surgical team ready to operate immediately if things change. Non-operative management is not a passive approach. It’s active surveillance.
How It Differs in Children
Children with epidural hematomas often present with subtler signs than adults. Nearly 40% of pediatric patients arrive with a completely normal level of consciousness. The most common finding is simply a scalp bruise or swelling (86% of cases), followed by loss of consciousness (66%), vomiting (34%), headache (27%), and seizures (12%). Because symptoms can be so mild initially, there’s a real risk of delayed diagnosis in younger patients.
The clinical course in children tends to be somewhat more favorable. Hematomas in children grow more slowly than in adults, rebleeding after surgery is less common, and mortality rates are lower in the pediatric population. Surgeons typically use a lower volume threshold for intervention in children, operating when the hematoma exceeds 20 cubic centimeters rather than the 30 cubic centimeter cutoff used for adults.
Survival and Recovery
Outcomes depend heavily on how quickly the hematoma is identified and treated. The critical factors are the time between injury and surgery, the person’s age, their neurological status before the operation, and whether there are additional injuries. In one large study of 268 surgically treated patients, the mortality rate was about 12%. When treatment is prompt and the person hasn’t deteriorated too far before surgery, outcomes are considerably better.
Recovery after surgical evacuation follows a general pattern. Most neurological improvement happens within the first six months, with continued gains possible over the following two years. Common lingering issues include headaches, difficulty concentrating, memory problems, dizziness, anxiety, and in some cases, weakness or speech difficulties. These post-injury symptoms gradually improve for most people, but the degree of recovery depends on how much brain compression occurred before the blood was drained.
The single most important factor in surviving an epidural hematoma is time. A person who is treated before they lose consciousness has a fundamentally different prognosis than someone who arrives in a coma. This is why any head injury followed by a period of worsening symptoms, even after an initial period of feeling fine, warrants immediate emergency evaluation.