<unk>  is a rare bone cancer that is diagnosed in only about 300 patients in the U.S. each year.<unk>  accounts for 1% of intracranial tumors and 4% of all primary bone tumors. It occurs exclusively in the axial skeleton and has a predilection for the sacrum (50%), base of the skull (35%), and mobile spine (15%). The cells that give rise to arise from the notochord. The notochord is an important structure in the early embryonic life that degenerates before birth. However, even after birth, some cells from the notochord remain in bones at the base of the skull, vertebrae, and the coccyx. Rarely, one of these cells, which are called notochord remnants, undergoes changes that give rise to a<unk> . Since<unk> s arise in bone, they are usually extradural and result in local bone destruction. On gross pathology, gelatinous mucoid substance, necrosis, hemorrhage, and calcification are characteristic findings of<unk> . On microscopic histopathological analysis, vacuolated cells with eccentric nucleus, physaliphorous cells, cytological atypia, and high mucin content within cytoplasm are characteristic findings of<unk> . Symptoms of<unk>  include radicular pain and sensory deficit related to nerve root compression. Clival<unk>  must be differentiated from chondrosarcoma of skull base, plasmacytoma, meningioma of skull base, pituitary macroadenoma, and ecchordosis physaliphora. Vertebral<unk>  must be differentiated from chondrosarcoma, giant cell tumor of bone, spinal metastases, plasmacytoma, and spinal lymphoma. The incidence of<unk>  is approximately 0.1 per 100,000 individuals in the United States.<unk> s may appear at any age, but are most commonly noticed among patients older than 30 years of age. Men are more commonly affected with<unk> s than females.<unk>  does not usually spread to other bones but can recur after treatment. Prognosis is generally poor, and the 10-year survival rate of patients with<unk>  is approximately 40%. CT scan may be diagnostic of<unk> . Findings on CT scan suggestive of<unk>  include expansile soft-tissue mass with a centrally located well-circumscribed destructive lytic lesion, marginal sclerosis, and irregular intratumoral calcifications. On MRI,<unk>  is characterized by calcifications and bony expansion. Chemotherapy for<unk> s usually results in low response rates. The predominant therapy for<unk>  is surgical resection. Adjunctive radiation may be required.
Chordoma
Brown tumor
Neuroma
Germinoma
Ameloblastoma
Medulloblastoma
Pineoblastoma
Schwannoma