Clivus Chordoma with an arachnoid Cyst, coincidence or causative factor؟

The clivus is the surface of a portion of the occipital and sphenoid bones in the base of the skull. (1)It is surrounded by the neurovascular structures of the brainstem, as well as internal carotid arteries. Tumors of the clivus can be benign (chordoma)or malignant (chondrosarcoma).(2) Chordomas are rare, aggressive, slow-growing, invasive, and locally destructive tumors that arise from the notochord, a structure that appears in embryonic stages and guides the growth of the bony skull and spine. Normally, notochordal remnants form part of the intervertebral discs. A chordoma occurs when additional notochordal cells are enclosed by the developing bones. Although these tumors are benign and slow-growing, they may invade nearby structures and destroy surrounding tissue and spread to other parts of the body.(2) Most arachnoid cysts are probably present at birth, or develop soon after. Once they are formed, they are thought to remain stable, apparently in some kind of equilibrium with the rest of the intracranial space(3). We report a rare case of clivus chordoma associated with an arachnoid cyst