Skullbase

The skull base, or cranial base, is the irregular inferior surface of the skull that forms the floor of the cranial cavity. It supports the brain and provides a framework that separates intracranial contents from the nasal cavity, orbits, and facial skeleton. It also transmits cranial nerves and major vessels.

It is conventionally divided into the anterior, middle, and posterior cranial fossae. The anterior fossa comprises the orbital plates of the frontal bone, the ethmoid bone (cribriform plate), and parts of the sphenoid; it houses the frontal lobes and the olfactory apparatus. The middle fossa contains the sphenoid body and greater wings, the temporal squama and petrous parts, and includes the optic canal and numerous foramina that transmit cranial nerves II–VI. The posterior fossa, bordered by the occipital bone and parts of the temporal bone, houses the brainstem and cerebellum and contains openings such as the internal auditory meatus, jugular foramen, hypoglossal canal, and the foramen magnum.

Bony contributions come mainly from the frontal, ethmoid, sphenoid, temporal, and occipital bones. The basilar portion of the occipital bone and the clivus, the sphenoid body and dorsum sellae, and the petrous temporal bone are key structural elements. The skull base also includes cartilage-derived areas at the foramina lacerum and adjacent canals during life.

Clinically, skull base integrity is important in trauma, and skull base fractures can affect cranial nerves and vascular structures. Skull base tumors and surgical approaches, including endonasal and transbasilar routes, rely on detailed knowledge of the regional anatomy. Imaging with CT and MRI is routinely used to evaluate the skull base.