Fibrous Dysplasia

**Semantic type:** Neoplastic Process

**Definition:** A benign medullary neoplasm characterized by the presence of poorly organized and inadequately mineralized bone and intervening fibrous tissue, in varying proportions. It can be monostotic or polyostotic. The skull, femur, tibia, and humerus are the most frequently affected bones. It manifests with pain, deformities, and fractures. GNAS activating mutations are detected in the majority of cases.

**Synonyms:** - Fibrous Dysplasia of Bone