Middle Cranial Fossa

Middle cranial fossa is the centermost of the three fossae in the base of skull. It is narrow medially and widens laterally to the sides of the skull. It lodges the temporal lobes of the cerebral hemispheres.  It is formed by the following bones:

  • Body and greater wing of sphenoid bone
  • Parts of temporal bone
  • Parts of parietal bone

Boundaries:

The anterior boundary of the middle cranial fossa is formed by the lesser wing of sphenoid bone. The posterior boundary is formed by the superior sharp border of the petrous part of temporal bone.

Floor:

Floor of the middle cranial fossa, from medial to lateral side, is formed by the following bones:

  • Body of sphenoid bone
  • Greater wing of sphenoid bone
  • Squamous as well as petrous parts of temporal bone
  • Part of parietal bone

Features and contents:

Sphenoid bone:

The sphenoid bone resembles a bat having a centrally placed body with greater and lesser wings extending to both sides. The body contains the sphenoid air sinuses that are lined with mucous membrane and communicate with the nasal cavity. Like all other air sinuses of the skull, they serve as voice resonators.

Optic canal:

It is located anteriorly and transmits the optic nerve and the ophthalmic artery

Superior orbital fissure:

It is a slit-like opening between the lesser and the greater wings of the sphenoid bone. It transmits many important structures including the lacrimal, frontal, trochlear, oculomotor, nasociliary and abducent nerves as well as the superior ophthalmic artery.

Foramen rotundum and foramen ovale:

Foramen rotundum is situated behind the medial end of the superior orbital fissure, perforating the greater wing of the sphenoid. It transmits the maxillary nerve. Foramen ovale is situated posterolateral to foramen rotundum, also perforating the greater wing of sphenoid. It transmits both the large sensory root and the small motor root of the mandibular nerve.

Foramen spinosum:

It also perforates the greater wing of sphenoid, lying posterolateral to the foramen ovale. It transmits the middle meningeal artery into the cranial cavity.

Foramen lacerum:

It is large an irregularly shaped and lies between the apex of the petrous part of the temporal bone and the sphenoid bone. In life, the opening of this foramen is filled with cartilage and fibrous tissue and only small blood vessels pass through it.

Carotid canal:

It opens into the side of the foramen lacerum above the closed inferior opening. The internal carotid artery enters the foramen lacerum through this canal.

Impression for trigeminal ganglion:

Lateral to the foramen lacerum, on the apex of the petrous part of the temporal bone, there is an impression for the trigeminal ganglion.

Grooves on petrous bone:

On the anterior surface of the petrous bone (petrous part of temporal bone), there are two grooves for nerves. The larger medial groove is for the greater petrosal nerve (a branch of facial nerve) and the smaller lateral groove for the lesser petrosal nerve (a branch of tympanic plexus).

Arcuate eminence:

It is a rounded eminence found on the anterior surface of the petrous bone and is caused by the underlying superior semicircular canal.

Tegmen tympani:

It is a thin plate of bone that is actually a forward extension of the petrous part of temporal bone. From behind forwards, it forms the roof of the mastoid antrum, the tympanic cavity and the auditory tube. Tegmen tympani is clinically important because it is the only barrier that separates the infection in the tympanic cavity from the temporal lobe of the cerebral hemisphere.

Median part of middle cranial fossa:

As described above, the median part is formed by the body of sphenoid bone. It has following important structures:

Sulcus chiasmatis:

It lies in front and is related to the optic chiasma. It leads laterally to the optic canal on each side.

Tuberculum sellae:

It is an elevation that lies posterior to sulcus chiasmatis.

Sella turcica:

It is a deep depression behind the elevation (tuberculum sellae). It lodges the pituitary gland.

Dorsum sellae:

It is a square plate of bone that bounds the sella turcica posteriorly.

Posterior clinoid processes:

These are two tubercles on the superior angles of the dorsum sellae. They give attachment to the fixed margin of the tentorium cerebelli.

Cavernous sinus:

It is directly related to the side of the body of sphenoid bone. The oculomotor, trochlear and ophthalmic and maxillary divisions of trigeminal nerve pass along its lateral wall. The internal carotid artery and the abducens nerve pass through it.