What Is the Pterion?

The pterion is a meeting point of several bones in the human skull. It encompasses the area around the sphenoparietal suture. It's found on either side of the head in what is considered the temple region. It's not visible to the naked eye, nor can it be felt through touch.

There are four bones of the skull that come together to form the pterion: the frontal bone, the parietal bone, the greater wing of the sphenoid bone and the squamous part of the temporal bone. The frontal bone is located at the front of the head in the region often called the forehead. Part of this bone comes down into the face. It's called the zygomatic process, and it forms part of the bony ridge of the eye socket and the bony protrusion of the cheek, often called the cheekbone. The zygomatic process is actually a convergence of three bones: the frontal bone; the maxilla, or jawbone; and the temporal bone.

The temporal bone is located on the side of the head and is made up of four parts. Its squamous part joins to the parietal bone, which sits above it and forms the top of the head. The sphenoid bone sits in front of the temporal bone and joins with the parietal bone and the squamous temporal at the alisphenoid, also known as the greater wing of the sphenoid.

The pterion is considered the weakest part of the skull, and a blow to it can rupture the major artery that runs beneath it. The middle meningeal artery runs directly underneath the pterion, and it's a part of the maxillary artery, which is, itself, a major branch of the external carotid artery — a main artery of the neck and head. The middle meningeal artery branches away from the maxillary artery and supplies blood to the outer meninges, which are membranes that cover the brain.

There are three meningeal arteries that supply the meninges with blood: the posterior, the anterior and the middle. The middle one is the largest of the three, and rupturing this artery causes a kind of traumatic brain injury called an epidural hematoma or extradural hematoma. The terms "epidural" and "extradural" both refer to the dura mater, or the tissue surrounding the brain and spinal cord, also called the meninges. There are three layers of meninges: the dura mater, the pia mater and the arachnoid. The dura mater is the outermost layer of tissue.