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What is an epidural hematoma?

While subdural means below the dura, epidural means outside the dura (in fact, some physicians also call it “extradural”). An epidural hematoma is a mass of blood that accumulates between the skull and the dura mater, the brain’s tough outer membrane. The membrane also covers the spine, so epidural bleeds may also occur in the spinal column. Both subdural and epidural hematomas are intercranial hematomas i.e. volumes of blood that collect at the surface of the brain rather than inside it. Epidural hematomas are less frequent than subdural hematomas and it may occur alone or in combination with the latter.

What are the causes of epidural hematoma?

Epidural hematomas are usually due to trauma that breaks a blood vessel, usually an artery, which then leaks blood into the area between the dura mater and the skull or spinal column. In more than 70 percent cases, the vessels are torn by fractures of the squamous portions of the temporal and parietal bones, typically as the result of a severe head injury from violence, falls and motor vehicle or sports-related accidents. Epidural hematomas can also be caused by venous bleeding in infants and young children. Non-trauma causes include anticoagulant therapy, hemophilia, liver disease, aspirin use, systemic lupus erythematosus, and, rarely, lumbar puncture.

Physiology of epidural hematoma

Epidural hematoma takes shape as biconvex (lentiform, elliptical, or football-shaped) in appearance. The dura is closely applied to the inner table and, as the hematoma from the bleeding expands, the dura bulges inward, giving it the biconvex or lens-shaped

The physiology of epidural hematomas is considerably different from that of subdural hematomas. Epidural hematomas are well-localized and high pressure, whereas subdural hematomas are more widespread under lower pressure. The underlying small cortical vessels are normal in both acute and chronic subdural hematomas but are severely distorted in epidural hematomas. The appearance of these vessels, seen best in the lateral projection, can help differentiate the various types of extracerebral hematomas. Extension of the hematoma usually is limited by suture lines, owing to the tight attachment of the dura at these locations, although in a minority of cases it traverses the suture lines.

The most common epidural hematoma occurs in temporoparietal area and the middle meningeal artery (66%), although the anterior ethmoidal artery may be involved in frontal injuries, the transverse or sigmoid sinus in occipital injuries, and the superior sagittal sinus in trauma to the vertex. Bilateral epidural hematomas account for 2-10% of all acute epidural hematomas in adults but are exceedingly rare in children. Posterior fossa epidural hematomas represent 5% of all cases of epidural hematomas.

In spinal epidural hematomas, the peridural venous plexus usually is involved, though arterial sources of hemorrhage also occur. The dorsal aspect of the thoracic or lumbar region is involved most commonly, with expansion limited to a few vertebral levels.

Signs and Symptoms of epidural hematoma

Intercranial epidural hematoma

Epidural hematomas may not show any signs of injury at first, then rapidly develop into more severe symptoms. Patients often show symptoms of a “lucid interval” in which they have a short period of initial unconsciousness, wake up and feel better then seem to deteriorate. This is because of the gradual accumulation of blood in the epidural area which presses on the brain over time. As the mass of blood accumulates, it pushes the rigid inner wall of skull or the spinal column and thus increases pressure on the dura mater. Eventually, it then compresses delicate brain tissue or spinal cord. The length of the lucid interval varies from minutes to hours, depending on the severity of injury to the artery. When venous vessels are involved in the epidural hematoma, chronic or delayed manifestations may also occur. (continued)