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.
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, motor function, swallowing, sense of smell, balance and coordination
• MRI — Magnetic Resonance Imaging best delineates clival chordomas and chondrosarcomas from meningiomas. It uses a magnetic field rather than x-rays (radiation).
• CT Scan — Computed tomography combines a sophisticated x-ray with computer technology. CT scanning is helpful to delineate the bony involvement in clival tumors. Injections of iodine dye (contrast material) may be used to enhance the visibility of abnormal tissue during CT scans.
• Biopsy — A sample of tissue is taken and examined under a microscope. Biopsy is ultimately necessary to properly diagnose a clival tumor.
Planning and execution of clival tumor removal can be among the most complex and difficult procedures in skull-base surgery. Radical surgical resection is attempted when possible, as these tumors have a high incidence of recurrence if incompletely removed. Adjuvant radiotherapy with proton beam or gamma knife is used in cases of subtotal resection.