Posttraumatic subgaleal herniation of an intracranial cerebral arterial segment.

A rare case of extracranial herniation of an intracranial arterial segment is described in an elderly patient presenting with loss of consciousness following mild head trauma. Cross-sectional imaging of the brain revealed a temporal skull fracture with associated intra-axial and extra-axial bleeding, and a computed tomography angiogram of the head and cerebral digital subtraction angiogram performed a few hours later displayed a rare finding. A small segment of a parietal branch of the right middle cerebral artery (M4 segment) herniated through the skull fracture, which coursed into the extracranial subgaleal space overlying the fracture site, before coursing back into the intracranial compartment. There was no evidence of cerebral ischemia or vascular compromise. The presence of a subgaleal artery on computed tomography angiogram may point to herniation of intracranial artery. In the absence of knowledge of this entity, even basic routine emergency care such as application of a scalp bandage or suturing of a scalp laceration could potentially result in devastating complications of vascular compromise and stroke.