Middle cranial fossa

Fossa media cranii

Definition

The middle part of the cranial cavity, known as the middle cranial fossa, is located between the anterior and posterior fossae. It is bordered at the front by the posterior edges of the lesser wings of the sphenoid bone, the anterior clinoid processes, and a ridge that forms the front margin of the chiasmatic groove. At the back, it is bordered by the upper edge of the petrous portions of the temporal bones and the dorsum sellae. On the sides, it is bounded by the squamous temporal bone, sphenoidal angles of the parietals, and greater wings of the sphenoid.

One of the important features within the middle cranial fossa is the sella turcica, which is a depression resembling a saddle, located in the middle of the sphenoid bone. The raised posterior border of the sella turcica is formed by a bony ridge called the dorsum sellae, which has posterior clinoid processes on both ends. The raised anterior border is called the tuberculum sellae, which has middle clinoid processes at both ends. The posterior clinoid processes, along with the anterior ones, serve as attachments for the tentorium cerebellum. This dural partition separates the occipital lobes above from the brainstem and cerebellum below in the posterior cranial fossa. The depression between the dorsum sellae and tuberculum sellae is known as the hypophyseal fossa, where the pituitary gland is located. The hypophyseal fossa is covered by a dural partition called the diaphragma sellae.

In front of the sella turcica, there is a shallow depression called the suprachiasmatic sulcus. It extends between the two optic canals and is closely related to the optic chiasma.

Moving towards the sides, on both sides of the sella turcica, the floor of the middle cranial fossa consists of depressed cavity-like areas formed by the greater wing of the sphenoid and the squamous temporal bones. These areas house the temporal lobes of the brain.

There are several openings within the floor of the middle cranial fossa. The superior orbital fissure is a diagonal gap between the greater and lesser wings of the sphenoid bone. It serves as a conduit for various structures, including multiple cranial nerves responsible for eye movement (oculomotor, trochlear, abducent), the ophthalmic division of the trigeminal nerve and its branches, as well as blood vessels supplying the ocular region.

Other important openings include the foramen rotundum, foramen ovale, and foramen spinosum. The foramen rotundum allows the passage of the maxillary nerve (V2), which opens into the pterygopalatine fossa. The foramen ovale is an oval-shaped opening that serves as a passageway for the mandibular division of the trigeminal nerve, responsible for facial sensation and chewing. The foramen spinosum acts as a pathway for the middle meningeal artery. Behind the foramen ovale lies the intracranial opening of the carotid canal. Directly below this opening is the foramen lacerum. Although the foramen lacerum is closed by a cartilaginous plug during life, it is crossed by the internal carotid artery, which enters the cranial cavity through the carotid canal and travels above it in an attempt to enter the cavernous sinus.

Moving further back, the posterior boundary of the middle cranial fossa is formed by the anterior surface of the wedge-shaped petrous part of the temporal bone. Near the medial end of the petrous bone’s anterior surface, there is a slight depression known as the trigeminal impression. This is where the trigeminal ganglion is located. Lateral to the trigeminal impression, there are grooves and hiatuses on the anterior surface of the petrous bone for the greater and lesser petrosal nerves.

The petrous temporal bone contains the middle and inner ear structures within it. Just lateral to the hiatuses and grooves for the petrosal nerves, there is a rounded protrusion on the anterior surface of the petrous bone called the arcuate eminence. This indicates the location of the anterior semicircular canal. Anterolateral to the arcuate eminence is a depressed region called the tegmen tympani. It forms the roof of the middle ear cavity. All these structures are situated within the petrous temporal bone.

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Text written by Muhammad A. Javaid, MD, PhD © 2024 IMAIOS.

  • Drake, R.L., Vogl, A.W. and Mitchell, A.W.M. (2009). ‘Chapter 8: Head and Neck’ in Gray’s anatomy for Students. (2nd ed.) Philadelphia PA 19103-2899: Elsevier, pp. 824-826.


Comparative anatomy in animals

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