M01.02.004 The Posterior Cranial Fossa

The skull’s base isn’t a flat surface! It has three distinct depressions called cranial fossae, each housing a specific brain region. This article focuses on the posterior cranial fossa, the deepest and most posterior of the three.

Borders:

Imagine a box cradling the brainstem and cerebellum. That’s essentially the posterior cranial fossa. Here’s how it’s formed:

• Front (Anteromedial): Dorsum sellae, a bony bump on the sphenoid bone.
• Front-Sides (Anterolateral): Upper edges of the temporal bone’s petrous part.
• Back (Posterior): Inner surface of the occipital bone’s squamous part.
• Bottom (Floor): A combination of the temporal bone’s mastoid part and various parts of the occipital bone.

Residents:

The key residents of the posterior cranial fossa are:

• Brainstem: This vital structure connects the brain to the spinal cord and controls essential functions like breathing and heart rate. It consists of three parts: medulla oblongata, pons, and midbrain.
• Cerebellum: This cauliflower-shaped structure plays a major role in coordinating movement, balance, and posture.

Bonus Feature (Foramina):

Think of foramina as holes in the skull that allow nerves and blood vessels to pass through. Here are some important ones in the posterior cranial fossa:

• Temporal Bone: The internal acoustic meatus transmits the facial nerve (controls facial expressions), the vestibulocochlear nerve (hearing and balance), and the labyrinthine artery.
• Occipital Bone:
  • Foramen Magnum: This large opening allows the brainstem, spinal cord, and many nerves and blood vessels to connect.
  • Jugular Foramina: Located on either side of the foramen magnum, they transmit nerves like the glossopharyngeal and vagus (involved in swallowing and digestion) and blood vessels like the internal jugular vein.
  • Hypoglossal Canal: This narrow channel carries the hypoglossal nerve, responsible for tongue movement.
  • Cerebellar Fossae: These are paired depressions on the occipital bone’s inner surface that house the cerebellum.

Clinical Correlation: Cerebellar Tonsillar Herniation

High pressure inside the skull can cause a condition called cerebellar tonsillar herniation. Imagine the cerebellar tonsils (tissue from the cerebellum) squeezing down through the foramen magnum, compressing the brainstem. This can be life-threatening as the brainstem controls vital functions like breathing and heart rate.

Understanding the posterior cranial fossa’s anatomy is crucial for medical students as it helps diagnose and manage various neurological conditions.