Posterior cranial fossa

The posterior cranial fossa is a significant region in the lower part of the cranial cavity. This area is home to important structures like the brainstem and cerebellum.

The posterior cranial fossa has specific boundaries. The back of this fossa is formed by the squamous part of occipital bone, extending up to the grooves for transverse sinuses. Towards the front and sides, the boundaries are completed by the dorsum sellae and the sloping clivus, which are located in the middle, and the superior edges of the petrous temporal bones. The dorsum sellae is the raised back margin of the sellae turcica, whereas the clivus is a sloping bone prominence that extends from the dorsum sellae to the foramen magnum. Not only does the clivus provide structural support to the brainstem, but it is also an important landmark in diagnostic imaging. The margins of the posterior cranial fossa serve as attachment points for the tentorium cerebelli, a dural partition that separates the occipital lobes above from the brainstem and cerebellum.

Several grooves and openings within the posterior cranial fossa serve as passageways for different structures. The jugular foramen is a large opening located between the petrous part of the temporal bone and the occipital bone. Through this foramen, important structures such as the internal jugular vein, glossopharyngeal nerve (CN IX), vagus nerve (CN X), and accessory nerve (CN XI) pass. The hypoglossal canals are small openings in the occipital bone, situated below the jugular foramen and along the front of the foramen magnum. These canals allow the hypoglossal nerve (CN XII), a key nerve involved in controlling tongue movements, to pass through.

Located centrally at the base of the posterior cranial fossa, the foramen magnum is the largest opening in the human skull. It serves as an entrance where the spinal cord connects to the brainstem. In addition, the vertebral arteries, the meninges, and the spinal roots of the accessory nerve also pass through this opening.

On the posterior surface of the petrous part of the temporal bone, you can find the internal acoustic meatus. This small canal is situated just above the jugular foramen and serves as a pathway for the facial nerve (CN VII) and the vestibulocochlear nerve (CN VIII).

Within the posterior cranial fossa, there are grooves along the inner aspect of the occipital bone for the transverse sinuses. These grooves start from the midline internal occipital protuberance, extend laterally, and then dip downwards in an S-shaped fashion, forming the grooves for the sigmoid sinuses that eventually open into the jugular foramen. These grooves accommodate the transverse and sigmoid venous sinuses, which are important channels responsible for draining blood from the brain into the internal jugular vein. Additionally, there are other grooves such as the groove for the inferior petrosal sinus, found between the clivus and petrous bone (where the petrooccipital fissure is located), and the groove for the superior petrosal sinus along the upper edge of the petrous temporal bone.