The clivus is the surface of a portion of the occipital and sphenoid bones in the base of the skull. It is surrounded by the neurovascular structures of the brainstem, as well as both internal carotid arteries. Tumors of the clivus can be benign or cancerous; they can be classified as chordomas or chondrosarcoma.

Chordomas are rare, aggressive, slow-growing, invasive, and locally destructive tumors that arise from the notochordal, a structure that appears in embryonic stages and guides the growth of the bony skull and spine. Normally, notochord remnants form part of the intervertebral discs. A chordoma occurs when additional notochord cells are enclosed by the developing bones. These rare tumors are slow-growing and benign, but they may invade nearby structures and they tend to recur after treatment, can destroy surrounding tissue, and may spread to other parts of the body.

Chondrosarcomas, which are even rarer than chordomas, are tumors of the cartilage that the skull replaces during development, although their exact origin is unclear. Most of these tumors are slow-growing, although in rare cases they can be aggressive and malignant.

Males are affected more frequently than females, and this tumor has a propensity for local recurrence, direct extension from the primary site, and systemic and cerebrospinal fluid metastasis.

Diagnosis

Examination of some masses may allow a physician to determine their cause based on location, size, and consistency. In other cases, however, additional tests may be required, such as:

• Neurological exam — includes evaluation of eye movements, hearing, sensation, muscular movement, sense of smell, balance and coordination
• MRI — Magnetic Resonance Imaging can clearly show tumors near bones, smaller tumors, and brainstems masses. It uses a magnetic field rather than x-rays (radiation).
• CT Scan — Computed tomography combines a sophisticated x-ray with computer technology. It is less accurate than MRI but can help locate tumors or determine their types, detect swelling or bleeding, and evaluate the effects of treatments. Injections of iodine dye (contrast material) may be used to enhance the visibility of abnormal tissue during CT scans.
• PET (Positron Emission Tomography) and SPECT (Single Photon Emission Tomography) are useful after diagnosis to help determine the grade of a tumor or to distinguish between cancerous and dead or scar tissue. They involve injection with a radioactive tracer.
• Biopsy — A sample of tissue is taken and examined under a microscope to determine if it is malignant.

Treatment

Head and neck cancers may be treated by some combination of radiation therapy, chemotherapy, and surgery, depending on their nature. Treatments are determined by the cause of the mass. Planning and execution of clival tumor removal is perhaps the most difficult of skull-base surgery. Benign neck cysts and masses are usually removed by surgical excision, while radical resection and postoperative radiotherapy are well established as the treatment modalities for malignant lesions.