Posterior Cranial Fossa

Posterior cranial fossa is the posterior-most of the three fossae in the base of the skull. It lodges the parts of the hindbrain, namely, the cerebellum, pons and medulla oblongata.

Boundaries:

The posterior cranial fossa is bounded anteriorly by the superior border of the petrous part of temporal bone.  Posteriorly it is bounded by the internal surface of the squamous part of the occipital bone.

Floor:

The floor of the posterior cranial fossa is formed by the basilar, condylar and squamous parts of the occipital bone and the mastoid part of the temporal bone.

Roof:

Unlike the other two fossae of the base of the skull (anterior and middle cranial fossae), the posterior cranial fossa has a roof formed by the tentorium cerebelli, which is a fold of the dura. It intervenes between the cerebellum and the occipital lobes of the cerebral hemispheres.

Features and contents:

Foramen magnum:

It is a large opening in the occipital bone, occupying the central area of the floor of posterior cranial fossa. It transmits the medulla oblongata and its surrounding meninges. In addition, the ascending spinal parts of the accessory nerves and the two vertebral arteries also pass through it.

Hypoglossal canal:

It is situated above the anterolateral boundary of the foramen magnum. It transmits the hypoglossal nerve.

Jugular foramen:

It lies between the lower border of the petrous part of temporal bone and the condylar part of the occipital bone. It transmits a number of structures including the following:

  • Inferior petrosal sinus
  • Glossopharyngeal (IX), Vagus (X) and Accessory (XI) cranial nerves
  • Sigmoid sinus (becomes the internal jugular vein below the foramen)

Internal acoustic meatus (Internal auditory meatus):

It is a canal in the petrous part of the temporal bone that carries nerves (facial (VII) and vestibulocochlear (VIII)) from inside the cranium towards the middle and inner ear.

Internal occipital crest:

It is the prominent lower division of the cruciate eminence of the occipital bone. It runs upward in the midline posteriorly from the foramen magnum to the internal occipital protuberance. The small falx cerebelli is attached to it.