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The clivus is a structure that makes up part of the skull base, the area of the skull designed to protect the brain and separate it from other structures around the face and neck. This particular piece of skull base anatomy is located in the middle of the skull and is sometimes used as a landmark in medical imaging and surgery, as it is easy to identify and can help medical practitioners orient themselves inside a patient's head. In addition, certain medical issues can arise in and around the base of the skull and may be identified on medical imaging studies.
This term is derived from the Latin for “slope” or “incline,” a reference to the distinctive physical appearance of the clivus. It lies between the occipital and sphenoid bones. A small gap known as the petro-occipital fissure lies between the clivus and the neighboring temporal bone, and can also be used as a landmark in clinical procedures involving the skull, as well as in imaging studies involving the base of the skull. The clivus is located behind the sphenoid sinus and provides support for the part of the brain known as the pons.
One issue in this area is a rare tumor known as a chordoma. Chordomas grow in the skull as a result of the entrapment of specialized cells known as notochord cells during fetal development. The cells are surrounded by bone, but continue developing, eventually causing a tumor to appear. Although chordomas grow slowly, they can be difficult to eradicate. The slow growth works in the favor of practitioners, as the cancer is hard to treat, but develops so slowly that the patient may die of natural causes before the cancer causes serious medical problems.
Another type of growth that can be located inside the clivus is a chondrosarcoma, a cancer arising from cartilage cells. These cancers occur when something goes awry with the division and replication of cartilage, causing the cells to grow uncontrollably. As the tumor develops, it puts pressure on the brain, and the patient will start to develop neurological symptoms. Both kinds of cancer can be seen clearly on medical imaging studies of the midbrain.
As an anatomical landmark, the clivus can help practitioners locate an area of interest in the brain on an imaging study, and acts as a quick pointer to help people find the pons. In surgery, using landmarks is very important, as surgeons want to avoid damage to the brain and are working in a very limited and sometimes confusing space. Being able to use skull anatomy as a frame of reference helps the surgeon stay in the right place.