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exostosis ex·os·to·sis (ěk'sŏ-stō'sĭs)
n. pl. -ses (-sēz)
A projection that is capped by cartilage and arises from a bone that develops from cartilage. Also called hyperostosis, poroma.
solitary benign tumour that consists partly of cartilage and partly of bone. Osteochondromas are common and may develop spontaneously following trauma or may have a hereditary basis. No treatment is required unless the tumour interferes with function, in which case it should be surgically removed. Rarely, a solitary osteochondroma will become malignant in adulthood, giving rise to a chondrosarcoma.