Ans. BSolitary bone cyst is the diagnosis of a 12 years old boy, who presents with a symmetric, expansile cystic lesion in the proximal humerus.Solitary Bone Cyst:Common in first two decades, primarily between 5-15 yearsMore common in malesMC site: Proximal humerus (50-60%) >Femur (25-30%)Cyst appears as centrally radioluscent lesions, on the metaphyseal side of the growth plate of a long boneTreatment:CurettageMethylprednisolone acetate injection into lesionRadiographic contrast injection into lesionIntralesional injection of sclerosing agentsSolitary Bone Cyst (Unicameral Bone Cyst)Common in first two decades, primarily between 5-15 yearsQMore common in malesQMC site: Proximal humerusQ (50-60%) >Femur (25-30%)It is not a true cystdeg because not lined by endothelial cells but lined by fibrous tissue and blood vesselsClinical Features:Asymptomaticdeg unless presents as a fractureRadiological Investigations:Cyst appears as centrally radioluscent lesionsQ, on the metaphyseal side of the growth plate of a long boneCoex is thinned but intactQFallen fragment sign" may present indication that the lesion is fluid filled rather than solidQOther tests are usually not required except in unusual locations such as pelvis. In such locations MRI or CT is indicatedMRI can document extent of the lesion and its cystic natureQMRI helps in distinguishing unicameral cyst (SBC) from aneurysmal bone cyst (ABC), giant celltumor (GCT) and fibrous dysplasiaQTreatment:CurettageQMethylprednisolone acetateQ injection into lesionRadiographic contrast injectionQ into lesionIntralesional injection of sclerosing agentsQ