John M. Barkley
L. Anne Hayman
Pedro J. Diaz-Marchan
The epidural space is another potential space that exists between the inner table of the skull and the closely adherent dura. Collections in the epidural space may dissect between these tissue layers to create an extra-axial epidural collection. Because of the firm attachment of the dura to the inner table of the skull, epidural hematomas tend to be smaller and more confined than the larger, subdural hematomas. Acute epidural hematomas result from injury to the middle meningeal artery or its branches due to fractures of the squamosal portion of the temporal bone (2).
Occasionally, acute epidural hematomas contain air within them. These air containing epidural hematomas are associated with fractures that communicate with the sinuses or extra-cranially (3). Ninety-five percent of epidural hematomas are associated with skull fractures and are supratentorial, typically unilateral (1).
Injuries of the dural venous sinuses may also lead to epidural hematomas (1). Injuries at the vertex of the skull may lead to disruption of the superior sagittal sinus, creating an epidural hematoma that crosses the midline. The collections typically appear biconvex, much like a lens, between the brain and skull on axial CT images. Unlike subdural hematomas, epidural hematomas can cross the midline. However, these collections are outside of the dura and cannot cross suture lines, for the dura is firmly attached to the skull at the sutures. If an acute epidural hematoma presents infratentorially, it is usually associated with trauma to the posterior fossa or fracture of the occipital bone (4, 5). An extra-axial hematoma in the posterior fossa is usually epidural in nature and typically unilateral (6). Rarely, acute epidural hematomas may be bilateral in approximately 5 percent of patients (Figure 11-11). When these collections are bilateral, they are often bifrontal in location (7).
Approximately one-third of patients with epidural hematomas are lucid clinically prior to neurological deterioration (2). Like all other forms of acute hemorrhage on CT, acute epidural hematomas are hyperdense (bright) compared to brain. These hematomas evolve to become isodense, then hypodense (dark) compared to brain over several days to weeks. Like any extra-axial collection, epidural hematomas will exert mass effect on the underlying brain and result in effacement of sulci and ventricles.
When severe, these collections present with midline shift and herniation. In contrast to a peripherally located hemorrhagic contusion, epidural hematomas will typically form obtuse angles with the underlying brain, revealing their extra-axial location.
The mortality rate is lower for epidural hematomas (10 percent) when compared to subdural hematomas. The reported mortality rate is variable and ranges from 20 to 90 percent (1, 2, 8). Because of firm dural attachments, there is usually a tamponade effect for epidural hematomas, while subdural hematomas are less confined and may be larger or appear in a delayed fashion as discussed above. Most epidural hematomas are acute and are detected during the initial imaging work-up. Occasionally a patient may present subacutely with a delayed epidural hematoma. About 6–13 percent of epidural hematomas are delayed in presentation while some authors have reported this as high as 30 percent (8).
Original: Brain Injury Medicine. Principles and Practice
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