What Is the Posterior Fossa?

The base of the skull is divided into three cranial fossae: posterior, middle and anterior. The posterior fossa, or posterior cranial fossa, is the deepest and largest and is defined by the occipital bone of the skull. Within this fossa are two critical brain areas: the brain stem and the cerebellum. These areas of the brain control the autonomic nervous system, coordination and movement. Cranial nerves VII through XII exit the skull through the posterior fossa, joining the spinal cord and connecting the brain with the rest of the body.

Found within the posterior fossa is the brain stem. It consists of the midbrain, the pons and the medulla. The brain stem contains key cranial nerves including the facial nerve, glossopharyngeal nerve, vagus nerve, accessory nerve and hypoglossal nerve. The brain stem is responsible for the vital autonomic functions of breathing, heart rate, blood pressure, digestion, perspiration and salivation. Damage to the skull in the area can result in death or permanent disability.

The cerebellum is the area of the brain responsible for movement, balance and coordination. Within the posterior fossa, the cerebellum is divided into two hemispheres separated by a thin area called the vermis. Through the spinal cord, the cerebellum receives information from muscles and sends information to the muscles. This sensory loop provides proprioceptive and kinesthetic information — information related to movement, equilibrium, position and pain. This finely tuned feedback loop allows dancers and athletes to develop amazing muscle control.

The spinal cord passes through the foramen magnum, a centrally located opening in the posterior fossa. The deep grooves in this fossa also contain the transverse sinuses and sigmoid sinuses. These sinuses are veins that collect blood from the brain and allow it to be recirculated through the heart.

Many diseases affecting the brain can occur in the area. Cancer in this area is often primary and can arise from the brain itself, the cranial nerves, the meninges, or the skull. These cancer tumors are more common in children and make up the majority of childhood brain tumors. Tumors growing in this area can block the flow of spinal fluid, causing increased pressure on the brain and brain stem. Infections in the head and neck can spread to the posterior fossa, as well, and strokes or bleeds are not uncommon in the cerebellum or brain stem because of the major blood vessels that pass through this fossa.