Herniation of an enlarged middle cerebral artery through a temporal bone defect in association with an arteriovenous malformation.

We present a previously undescribed variant of the middle cerebral artery (MCA) protruding through a defect in the temporal bone, associated with a large arteriovenous malformation (AVM). The patient, a 59-year-old male, presented with a large right frontoparietal AVM with feeding aneurysms and a recent haemorrhage. Preoperative imaging demonstrated a tortuous right MCA feeder abutting the anterosuperior temporal bone in the region of the pterion. An associated temporal bone defect was visible. The patient underwent a pterional craniotomy for surgical clipping of aneurysms associated with the AVM. On reflection of the temporalis muscle, the MCA branch was transected as it coursed through a defect in the temporal bone. This patient demonstrates that the MCA may deviate from its usual anatomy and herniate through a defect in the skull. Because a pterional craniotomy is such a common surgical approach, knowledge and anticipation of such anatomic variants are essential to avoid catastrophic vascular injury during surgery.