M01.02.003 The Middle Cranial Fossa

The skull base has three distinct depressions: the anterior, middle, and posterior cranial fossae. Each fossa houses a specific part of the brain.

This guide focuses on the middle cranial fossa, also known as the central skull base. It’s a complex area crucial for understanding neuroanatomy and relevant clinical applications.

Location and Shape:

• Located centrally in the cranial floor, resembling a butterfly shape.
• The central part holds the pituitary gland, while the lateral parts accommodate the temporal lobes of the brain.

Borders:

• Anteriorly and laterally: Lesser wings of the sphenoid bone (triangular projections).
• Anteriorly and medially: Limbus of the sphenoid bone (bony ridge).
• Posteriorly and laterally: Superior border of the petrous part of the temporal bone.
• Posteriorly and medially: Dorsum sellae of the sphenoid bone (large superior projection).
• Floor: Body and greater wing of the sphenoid bone, squamous and petrous parts of the temporal bone.

Contents:

Central Portion:

• Sella turcica (Turkish saddle): A bony prominence shaped like a saddle that houses and supports the pituitary gland. It has three parts:
  • Tuberculum sellae: Forms the anterior wall and sits behind the chiasmatic sulcus (groove between optic canals).
  • Hypophysial fossa (pituitary fossa): Depression in the sphenoid body that holds the pituitary gland.
  • Dorsum sellae: Forms the posterior wall, separating the middle from the posterior cranial fossa.
• Clinoid processes: Bony projections surrounding the sella turcica.
  • Anterior clinoid processes: Arise from the lesser wings of the sphenoid bone.
  • Posterior clinoid processes: Superior projections of the dorsum sellae. Both sets serve as attachment points for the tentorium cerebelli (membrane dividing the brain).

Lateral Parts:

• Formed by the sphenoid’s greater wings and the temporal bones’ squamous and petrous parts.
• Support the temporal lobes of the brain.
• Contains numerous foramina (holes) for nerves and vessels to enter/exit the cranium.

Foramina:

• Optic canals: Transmit optic nerves (CN II) and ophthalmic arteries to the orbits. They’re connected by the chiasmatic sulcus.
• Sphenoid foramina (lateral to central part):
  • Superior orbital fissure: Opens into the orbit, transmitting oculomotor (CN III), trochlear (CN IV), ophthalmic (V1), abducens (CN VI) nerves, ophthalmic veins, and sympathetic fibers.
  • Foramen rotundum: Opens into the pterygopalatine fossa, transmitting the maxillary branch of the trigeminal nerve (V2).
  • Foramen ovale: Opens into the infratemporal fossa, transmitting the mandibular branch of the trigeminal nerve (V3) and the accessory meningeal artery.
  • Foramen spinosum: Opens into the infratemporal fossa, transmitting the middle meningeal artery, vein, and a meningeal branch of CN V3.
• Temporal bone foramina:
  • Hiatus of the greater petrosal nerve: Transmits the greater petrosal nerve (facial nerve branch) and the petrosal branch of the middle meningeal artery.
  • Hiatus of the lesser petrosal nerve: Transmits the lesser petrosal nerve (glossopharyngeal nerve branch).
  • Carotid canal: Located behind the foramen ovale, transmits the internal carotid artery supplying blood to the brain. The deep petrosal nerve also passes through this canal.
• Foramen lacerum: Located at the junction of sphenoid, temporal, and occipital bones. Filled with cartilage in life, pierced only by small blood vessels.

Clinical Relevance: Pituitary Surgery

The pituitary gland’s location in the sella turcica makes it accessible for surgical procedures in cases of pituitary tumors. Endoscopic transsphenoidal surgery is a common approach. An endoscope inserted through the nose or an incision (rarely) visualizes and removes the tumor in sections.