Cranial Calvaria: Structure, Function & Diseases

The cranial calvaria, in Latin calvaria, is the bony roof of the skull and consists of flat, flattened bones (ossa plana). It is also part of the neurocranium, the skull, and at the same time the bone which encloses the brain. The flat bones are connected by so-called sutures: these are seams between two bones, made of connective tissue. Since sutures are inauthentic joints, they grow together into ossified synostoses as we age; synostoses are the fusion of bones that were once connected by connective tissue.

What is the calvaria of the skull?

The cranial dome serves to protect the brain as well as the sensory organs, thus preventing damage to the brain. Its shape makes it resemble a helmet, especially because of the flat bones (ossa plana).

Anatomy and structure

The calvaria is divided into four following bones:

  • Frontal bone (Os frontale),
  • Two parietal bones (Os parietale, pl. Ossa parietalia),
  • As well as occipital bone (Os occipitale).

These bones are connected by the sutures, the connective tissue sutures between bones. The Os frontale can be seen as a part of the facial skull, it forms the anterior cranial roof and thus the upper wall of the cranial cavity. The two parts of the frontal bone are also connected by a suture of bone. The frontal bone is divided into the three sections, the frontal bone scale (squama frontalis), the pars orbitalis, which forms the orbital roof, and the pharynx (Greek for “pharynx”). The frontal bone scale is the largest part of the frontal bone, it forms the frontal area and lies above the orbit (eye sockets). It contains the so-called frontal sinuses, which are filled with air. They are arranged in pairs and lined with mucosa. The frontal sinuses are separated by a septum and open into the middle nasal meatus. In addition, the squama frontalis is divided into an inner as well as an outer surface. The outer surface of the squama frontalis (frontal bone scale) is convex and usually shows an anterior suture connecting two anterior bones. On each of the two frontal bones, situated in the middle area, are the frontal tuberosities. These usually look asymmetrical and different in each; they are especially common in skulls of young people. Below the tuber frontale at the lower part of the frontal bone are the eyebrow arches, which are connected by the so-called glabella, the skin region between the eyebrows. The part of the pars orbitalis consists of two thin, triangular-shaped plates, the orbital plates; together, these form a bulge between the orbitals. The ossa parietalia form a central part of the cranial dome and lie below the vertex. They are located on either side of the skull and form large portions of the cranial dome as well as the lateral wall of the ossified brain capsule. They are curved inward (concave) on the inner side and outward (convex) on the outer side. On the inner side of the parietal bones run furrows of the arteries, which displace the bones due to arterial pressure. The parts of the parietal bone are connected by three sutures: The sagittal sutura connects the left and right parietal bones, the coronal sutura connects the parietal bone to the anterior frontal bone, and the lambdoid sutura connects it to the occipital bone. For vessels, there are small holes in the bones, called foramina parietalia, through which the emissary veins, among others, pass. The occipital bone, or os occipitale, is the third part of the cranial dome and is located near the junction of the neck, thus forming the posterior termination of the cranial cavity. Also in the Os occipitale is an opening for the twelfth cranial nerve (Canalis nervi hypoglossi), one of the nerves that arise directly from nerve collections of the brain. Divided, the occipital bone is divided into three parts:

  • Bottom part, which belongs to the posterior base of the skull,
  • Side part,
  • Occipital scale, the rear side.

Function and tasks

As part of the entire skull, the skullcap is responsible for protecting the brain as well as blood vessels, lymphatics and nerves. Furthermore, there are several openings in the skullcap for cranial nerves and veins. In addition, the cranial cap gives the head its round shape.

Diseases

The best-known impairment of the cranial vault is cranial dome fracture: this is a multiple fracture of the cranial vault and can result from brain, or soft tissue, swelling. Cranial nerves, veins and other vessels can also be damaged with a fracture. Symptoms for a calvaria fracture can vary, but include bruising under the eyes, swelling of the eyelids, or disturbance of the sense of smell. Another disease that can accompany due to the bone is bone metastases, which are daughter tumors and developed due to a spatially separated tumor. Signs of metastasis include bone pain, especially in the neck in the case of calvaria metastasis.