The middle cranial fossa is a central depression in the floor of the cranial cavity, lying between the anterior and posterior cranial fossae. It accommodates vital brain structures, particularly the temporal lobes, and contains multiple foramina that allow the passage of critical neurovascular elements. The middle cranial fossa is bordered by thick bony ridges and forms the central portion of the cranial base. Due to its anatomical complexity and clinical significance, understanding this region is essential for medical professionals in neurology, neurosurgery, and radiology.
Boundaries and Bones of the Middle Cranial Fossa
Anterior Boundary
The anterior limit of the middle cranial fossa is defined by the lesser wings of the sphenoid bone. These bony ridges separate it from the anterior cranial fossa and contribute to the superior orbital fissure.
Posterior Boundary
The posterior boundary is formed by the petrous part of the temporal bone and the dorsum sellae, which separates it from the posterior cranial fossa.
Lateral Boundary
Laterally, the fossa extends toward the squamous part of the temporal bone and the parietal bones, forming the walls of the temporal region of the skull.
Contributing Bones
- Sphenoid bone: Includes the body, greater wings, and the sella turcica.
- Temporal bone: Comprises the squamous and petrous parts, providing support and protection for neurovascular structures.
- Parietal bone: Forms the upper boundary of the fossa laterally.
Key Anatomical Features
Sella Turcica
This saddle-shaped depression in the sphenoid bone houses the pituitary gland. It is composed of several parts:
- Tuberculum sellae: The anterior boundary.
- Hypophyseal fossa: The central pit where the pituitary rests.
- Dorsum sellae: The posterior wall of the sella turcica.
Optic Canal
Located at the junction of the lesser wing and the body of the sphenoid, the optic canal transmits the optic nerve (CN II) and the ophthalmic artery from the cranial cavity into the orbit.
Superior Orbital Fissure
A slit-like opening between the lesser and greater wings of the sphenoid, this fissure allows the passage of cranial nerves III, IV, V1 (ophthalmic division), and VI, as well as the superior ophthalmic vein.
Foramen Rotundum
This small circular opening in the greater wing of the sphenoid transmits the maxillary division of the trigeminal nerve (V2) to the pterygopalatine fossa.
Foramen Ovale
This oval-shaped foramen transmits the mandibular division of the trigeminal nerve (V3), the accessory meningeal artery, and sometimes the lesser petrosal nerve.
Foramen Spinosum
Located posterior and lateral to the foramen ovale, it transmits the middle meningeal artery and vein, along with the meningeal branch of V3.
Carotid Canal
This canal allows the internal carotid artery to enter the cranial cavity and pass near the foramen lacerum before supplying the brain.
Contents of the Middle Cranial Fossa
Temporal Lobes
The middle cranial fossa houses the temporal lobes of the brain. These lobes are responsible for auditory processing, memory, and language comprehension. Their location in the fossa makes this region crucial for preserving cognitive and sensory functions.
Pituitary Gland
Resting within the sella turcica, the pituitary gland plays a pivotal role in hormonal regulation and is connected to the hypothalamus via the infundibulum. Any lesions in this area can affect hormonal balance and vision due to proximity to the optic chiasm.
Cavernous Sinus
Located on either side of the sella turcica, the cavernous sinuses contain important structures:
- Internal carotid artery
- Oculomotor nerve (CN III)
- Trochlear nerve (CN IV)
- Ophthalmic and maxillary nerves (CN V1, V2)
- Abducens nerve (CN VI)
Infections or thrombosis in this area can result in severe neurological complications.
Clinical Relevance
Middle Cranial Fossa Fractures
Fractures in this area can affect the integrity of the cranial base and often lead to complications such as cerebrospinal fluid (CSF) leaks, cranial nerve damage, and hearing loss. The involvement of the carotid canal can pose a life-threatening risk.
Pituitary Tumors
Due to the gland’s location in the sella turcica, pituitary adenomas can compress surrounding structures. Symptoms include visual disturbances (e.g., bitemporal hemianopia), endocrine abnormalities, and headaches.
Temporal Lobe Epilepsy
Temporal lobe epilepsy originates in the regions housed within the middle cranial fossa. Seizures may manifest with auditory hallucinations, memory issues, or even déjà vu experiences.
Surgical Access and Considerations
Middle Cranial Fossa Approach
Neurosurgeons use the middle cranial fossa approach for removing tumors, repairing CSF leaks, and treating trigeminal neuralgia. This route provides access to the internal auditory canal, the petrous apex, and Meckel’s cave.
Risks and Complications
Surgeries in this area carry potential risks including injury to cranial nerves, damage to the internal carotid artery, and postoperative complications such as meningitis. Preoperative imaging and microsurgical techniques are essential to minimize risks.
Radiological Imaging
CT and MRI Scans
CT scans are effective in detecting fractures, bony abnormalities, and sinus conditions, while MRI is preferred for visualizing soft tissue structures like tumors, cranial nerves, and vascular abnormalities.
Common Pathologies Seen on Imaging
- Skull base fractures
- Infiltrative lesions of the cavernous sinus
- Enlarged pituitary gland or mass lesions in the sella turcica
Development and Anatomy in Pediatrics
Ossification and Growth
In newborns and children, the bones forming the middle cranial fossa are not fully ossified. The shape and depth of the fossa change as the brain and skull grow. Fontanelles and sutures eventually close during early childhood.
Congenital Anomalies
Conditions like craniosynostosis can lead to abnormal development of the cranial base, including the middle fossa. Early diagnosis and surgical correction may be necessary to prevent intracranial pressure buildup.
The middle cranial fossa is a central and structurally complex part of the cranial floor, containing essential neural and vascular elements and housing critical regions like the temporal lobes and pituitary gland. Its numerous foramina allow the passage of cranial nerves and arteries that supply vital functions. Clinically, this region is of high importance due to its involvement in traumatic injuries, tumors, infections, and surgical procedures. Comprehensive knowledge of its anatomy is indispensable for healthcare providers dealing with neurological and cranial conditions, and for accurately interpreting diagnostic imaging.