Thoracic fibrous dysplasia (FD) is a benign, osseous chest wall tumor. It originates from bone marrow and accounts for 30–50% of all benign osseous neoplasms in the chest wall. In FD, normal bone marrow is replaced by fibrous stroma and immature bone. We present a rare case in which massive intrathoracic polyostotic FD originating from the rib was diagnosed and treated. The extrathoracic part of the tumor appeared stable and unalarming for decades; however, in hindsight, the intrathoracic part significantly progressed, eventually leading to symptoms. The tumor was removed through a hemi-clamshell approach, which allowed adequate visualization and control of mediastinal structures. After establishing the diagnosis of FD, regular follow-up imaging is crucial for timing of a surgical intervention to prevent symptoms, impairment of quality of life, and unnecessarily complex resections.
