Fibrous dysplasia of rib presenting as a cystic mass in the lung

Fibrous dysplasia (FD) is a benign skeletal disorder that can affect one bone (monostotic form) or multiple bones (polyostotic form). It is a non-inherited bone disease, in which abnormal differentiation of osteoblasts leads to replacement of normal marrow and cancellous bone by immature bone with fibrous stroma. It is often asymptomatic and incidentally detected on radiographs. We report this rare disorder in a 22-year-old lady who presented to us with cough and breathlessness. Her chest radiograph showed a cystic mass extending into the chest wall. On computed tomography scan, mass turned out to be FD of the second rib. Histopathology of the lesion confirmed the diagnosis.