History: 19-year-old woman in motor vehicle accident
Findings: An axial CT scan with bone reconstruction shows a depressed right parietal skull fracture. The same image rewindowed for soft tissue structures reveals a biconvex hyperdense extraaxial mass. There is also subfalcial herniation with leftward displacement of the gray-white matter interface of the right parietal lobe.
Subfalcine herniation, the most common cerebral herniation pattern, is characterised by displacement of the brain (typically the cingulate gyrus) beneath the free edge of the falx cerebri due to raised intracranial pressure.
The cingulate gyrus lies on the medial aspect of the cerebral hemisphere. It forms a major part of the limbic system which has functions in emotion and behaviour. The frontal portion is termed the anterior cingulate gyrus (or cortex) 1-2.
Epidural or extradural hematoma (haematoma), also known as an epidural hemorrhage, is a type of traumatic brain injury (TBI) in which a buildup of blood occurs between the dura mater (the tough outer membrane of the central nervous system) and the skull. The spinal cord is also covered by a layer of dura mater, so epidural bleeds may also occur in the spinal column. Often due to trauma, the condition is potentially deadly because the buildup of blood may increase pressure in the intracranial space, compress delicate brain tissue, and cause brain shift. The condition is present in one to three percent of head injuries. Around 15% – 20% of epidural hematomas are fatal.
Discussion: Epidural hematomas are the result of bleeding into the potential space between the outer of periosteal layer of the dura mater and the inner table of the skull. They are present in less than 5% of patients imaged for cranial trauma. Epidural bleeding most commonly arises from disruption of the meningeal arteries, although laceration of the dural venous sinus and venous ‘oozing’ from meningeal venous injury may have similar results. Skull fractures are present in approximately 90% of patients with epidural hematomas. Because epidural hematomas are located external to the outer or periosteal dural layer, (which is firmly bound at the dural margin) they rarely cross sutures and typically appear biconvex. CT without contrast is the examination of choice for suspected epidural hematomas. Typical imaging features include a hyperdense biconvex extraaxial mass displacing brain with secondary brain herniation. Active bleeding is indicated by areas of inhomogeneity within an epidural hematoma. Clinically, epidural hematomas are usually managed by emergent surgical evacuation. Interestingly, a patient with an epidural hematoma may initially be neurologically intact, only to develop the rapid onset of severe neurologic compromise (he so-called ‘lucid interval’). Because of the morbidity and mortality associated with untreated epidural hematomas, all patients with severe head trauma or unconsciousness after head trauma are imaged for this and other brain injuries.
Aunt Minnie’s Pearls
- 90% of epidural hematomas are associated with a skull fracture
- These lesions are usually biconvex and do not cross sutures