The pterion is a crucial anatomical landmark on the human skull, representing a region where four cranial bones converge. These bones are the frontal bone, parietal bone, temporal bone, and sphenoid bone. This area is relatively thin and is known for its clinical significance due to the proximity of the middle meningeal artery, which runs just beneath it.
Location
The pterion is located on the lateral aspect of the skull, approximately two finger-widths above the zygomatic arch (cheekbone) and slightly behind the frontal process of the zygomatic bone. It lies in the region where the temporal fossa and the sphenoid ridge meet. The precise location can vary slightly between individuals, but it is generally found in this lateral aspect of the skull. The pterion’s exact position makes it an important reference point in both medical and anthropological contexts.
Structure
The pterion is a region on the human skull where several cranial bones intersect. It is an anatomically complex area due to the convergence of multiple bone sutures and the underlying structures.
Cranial Bones Involved
- Frontal Bone: The frontal bone forms the anterior part of the skull and contributes to the forehead and the upper part of the eye sockets. At the pterion, the frontal bone meets the other cranial bones, playing a key role in the overall structure.
- Parietal Bone: The parietal bone is a large, curved bone forming the upper sides and roof of the skull. It extends from the frontal bone at the front to the occipital bone at the back. At the pterion, the parietal bone meets the frontal, temporal, and sphenoid bones.
- Temporal Bone: The temporal bone is located on the side of the skull, housing structures of the ear and forming part of the cranial base. It contributes to the lateral aspect of the pterion. Specifically, the squamous part of the temporal bone is involved in forming the pterion.
- Sphenoid Bone: The sphenoid bone is a complex, butterfly-shaped bone located at the base of the skull. The greater wing of the sphenoid bone is the part that meets the other bones at the pterion.
Sutures Formed
Coronal Suture
The coronal suture is the joint between the frontal bone and the parietal bones. It extends across the top of the skull from ear to ear. At the pterion, the coronal suture intersects with other sutures, contributing to the complex structure.
Squamosal Suture
The squamosal suture is the joint between the parietal bone and the temporal bone. It runs along the side of the skull, curving around the ear. At the pterion, it meets with the other cranial sutures.
Sphenoparietal Suture
The sphenoparietal suture is the joint between the sphenoid bone and the parietal bone. It is located at the upper edge of the greater wing of the sphenoid bone and meets the coronal and squamosal sutures at the pterion.
Frontozygomatic Suture (Proximity)
Although not directly forming the pterion, the frontozygomatic suture, which is the junction between the frontal bone and the zygomatic bone, is located nearby. This proximity highlights the spatial complexity of the region.
Spatial Relationships and Characteristics
Thinness of the Bone
The pterion is characterized by the thinness of the bone in this region. The convergence of multiple bones results in a thinner section of the skull compared to other areas, which is significant in various medical contexts.
Temporal Fossa
The temporal fossa is a shallow depression on the side of the skull bounded by the temporal lines and the zygomatic arch. The pterion forms part of the floor of this fossa. It accommodates the temporalis muscle, which is involved in mastication (chewing).
Overlapping Bones
The bones at the pterion overlap slightly, creating a complex mosaic-like arrangement. This overlapping contributes to the structural integrity of the skull but also results in a relatively fragile area.
External and Internal Surfaces
Externally, the pterion is palpable as a slight depression or flattening on the lateral aspect of the skull. Internally, the bones at the pterion contribute to the formation of the anterior and middle cranial fossae, which house critical brain structures.
Function
The pterion, while primarily known as an anatomical landmark, serves several important functions due to its location and the structures it encompasses or affects. These functions include providing structural integrity, serving as a reference point in medical procedures, protecting underlying neurovascular structures, and influencing craniofacial dynamics.
Structural Integrity
Convergence of Cranial Bones
The pterion is where four cranial bones converge: the frontal, parietal, temporal, and sphenoid bones. This junction helps distribute mechanical forces across the skull, contributing to its overall structural stability. The overlapping and interlocking nature of these bones at the pterion enhances the skull’s ability to absorb and dissipate impact forces.
Support for Temporal Fossa
The pterion forms part of the floor of the temporal fossa, a shallow depression on the lateral aspect of the skull. This region accommodates the temporalis muscle, which is essential for mastication (chewing). The structural integrity of the pterion supports this muscle, enabling effective jaw movement.
Reference Point in Medical Procedures
Surgical Landmark
The pterion is a crucial landmark in neurosurgical procedures, particularly those involving the temporal lobe or the anterior and middle cranial fossae. Surgeons use the pterion as a reference point to guide craniotomies and other interventions, ensuring precision in accessing specific brain regions.
Radiological Marker
In radiology, the pterion serves as a key marker for interpreting cranial imaging. It helps radiologists identify the relative positions of cranial structures and assess any abnormalities or pathologies in the surrounding areas.
Anthropometric Measurements
The pterion is used in anthropometric studies to measure craniofacial dimensions and assess population-based differences in skull morphology. These measurements can aid in forensic identification and anthropological research.
Protection of Underlying Neurovascular Structures
Middle Meningeal Artery
One of the most critical functions of the pterion is its proximity to the middle meningeal artery, which runs just beneath this area. The bone at the pterion provides a protective barrier for this artery. Damage to the pterion, such as from trauma, can lead to a rupture of the middle meningeal artery, resulting in an epidural hematoma, a potentially life-threatening condition.
The pterion is near several cranial nerves, including branches of the trigeminal nerve, which provides sensation to the face and motor functions for mastication. The bony structure at the pterion helps protect these nerves from injury.
Influence on Craniofacial Dynamics
Temporalis Muscle Attachment
The pterion is part of the area where the temporalis muscle attaches. This muscle plays a crucial role in chewing and moving the jaw. The structural integrity of the pterion supports the attachment and functioning of the temporalis muscle, facilitating efficient jaw movements.
Cranial Shape and Development
The formation and position of the pterion can influence the overall shape and development of the cranium. Variations in the pterion’s structure can affect craniofacial symmetry and proportions, impacting both aesthetic and functional aspects of the skull.
