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Anatomy and Imaging of the Skull and Facial Bones
The skull consists of the calvarium, facial bones and mandible. The calvarium is the brain case and comprises the skull vault and skull base. The bones of the calvarium and face are joined at immovable fibrous joints, except for the temporomandibular joint, which is a movable cartilaginous joint.
The Skull Vault
The skull vault is made up of several flat bones, joined at sutures, which can be recognized on skull radiographs. The bones consist of the diploic space – a cancellous layer containing vascular spaces – sandwiched between the inner and outer tables of cortical bone. The skull is covered by periosteum, which is continuous with the fibrous tissue in the sutures. The periosteum is called the pericranium externally and on the deep surface of the skull it is called the endosteum. The endosteum is the outer layer of the dura. Within the structure, the diploic veins are large, valveless vessels with thin walls. They communicate with the meningeal veins, the dural sinuses and the scalp veins.
Detailed Bone Structure and Sutures
The frontal bone forms the front of the skull vault. It is formed by two frontal bones that unite at the metopic suture. The frontal bones join the parietal bones at the coronal suture. The junction of coronal and sagittal sutures is known as the bregma. The paired parietal bones form much of the side and the roof of the skull and are joined in the midline at the sagittal suture. Parietal foramina are paired foramina or areas of thin bone close to the midline in the parietal bones. They are often visible on a radiograph and may transmit emissary veins from the sagittal sinus. The occipital bone forms the back of the skull vault and is joined to the parietal bones at the lambdoid suture. The junction of the lambdoid and sagittal sutures is known as the lambda.
Bony Landmarks and Radiographic Features
Various landmarks can be identified on a lateral or frontal view of the skull. The following table summarizes key anatomical features identified in imaging:
| Category | Anatomical Structures |
|---|---|
| Bony Landmarks | Bregma, Vertex, Internal and external occipital protuberance, External auditory meatus, Styloid process, Clivus, Dorsum sellae, Pituitary fossa (sella turcica), Tuberculum sellae, Planum sphenoidale, Greater and lesser wings of sphenoid, Hard palate, and Foramen magnum. |
| Vascular Markings | Middle meningeal vessels (anterior and posterior branches), Transverse sinus, Diploic vein, and Diploic venous confluence (parietal star). |
| Sinuses and Air Cells | Frontal sinus, Sphenoid sinus, Ethmoid air cells, Maxillary sinus, and Mastoid air cells. |
| Sutures | Coronal, Sagittal, Lambdoid, Metopic, Zygomaticofrontal, Sphenotemporal, and Temporoparietal sutures. |
Anatomical Components of the Skull
As identified in clinical imaging, additional specific structures include:
- Crista galli and Perpendicular plate of ethmoid.
- Superior orbital fissure and Floor of orbit.
- Zygomatic process of frontal bone and Frontal process of zygomatic bone.
- Foramen rotundum and Petrous ridge.
- Condylar (mandibular) canal and Neck of mandible.
- Soft tissues: Soft palate and base of tongue.