The clivus is a bony formation at the base of the skull, often overlooked but crucial for supporting vital neurological structures. Understanding its role is important for comprehending the body’s overall function and potential medical considerations, as it is an area where various conditions can arise.
Anatomy and Location of the Clivus
The clivus, a term derived from Latin meaning “slope,” is a gentle bony surface centrally positioned within the posterior cranial fossa. This sloped structure extends from behind the dorsum sellae of the sphenoid bone down to the anterior edge of the foramen magnum, the large opening at the base of the skull. It is formed by the fusion of two bones: the basisphenoid (part of the sphenoid bone) and the basiocciput (part of the occipital bone). This fusion typically completes between 12 and 18 years of age.
The clivus has a quadrilateral shape, sloping anteriorly and superiorly from the foramen magnum towards the dorsum sellae. The brainstem, specifically the pons and medulla oblongata, rests directly upon its superior surface.
Vital structures are in close proximity to the clivus. The basilar artery, a major blood vessel supplying the brain, runs along its posterior surface. Laterally, it is adjacent to the internal carotid arteries, various cranial nerves, and the internal jugular veins. The sphenoid sinuses are located just anterior to the clivus.
Clinical Importance of the Clivus
The clivus provides protection for the brainstem, which controls essential bodily functions like breathing and heart rate. Its strategic location makes it susceptible to injury and disease, potentially leading to significant neurological consequences. High-impact trauma, such as severe accidents, can cause basilar skull fractures, including those of the clivus. These injuries can directly affect the brainstem or damage surrounding nerves and blood vessels, causing symptoms from cranial nerve palsies to life-threatening complications.
Tumors can originate or extend to the clivus. Chordomas are rare, slow-growing tumors that arise from remnants of the notochord, an embryonic structure. They are the most frequent clival tumor. Chondrosarcomas also originate here from cartilage. Other tumors, such as meningiomas, pituitary adenomas, and metastatic lesions from distant cancers, can also affect the clivus.
The clivus is an important area for neurosurgeons accessing the brainstem or pituitary gland. Surgical procedures here are intricate, often requiring specialized approaches to avoid damaging neurovascular structures. Advances in endoscopic techniques allow for less invasive access to clival lesions through the nose.
Medical imaging, particularly computed tomography (CT) and magnetic resonance imaging (MRI), is used to assess the clivus. These modalities help diagnose injuries, identify tumors, and evaluate pathology. MRI is useful for differentiating tumor types and assessing their invasion.