Fibrous dysplasia of the rib
Monostotic fibrous dysplasia (commonly abbreviated to FD) of the rib is the commonest benign bone lesion of the ribs. They are usually clinically silent and found incidentally. Occasionally they may cause pain, which is sometimes the result of a pathological fracture.
Malignant transformation is rare, being seen in less than 1% of cases, and most frequently presents as osteosarcoma, although fibrosarcoma, or chondrosarcoma are also seen. Usually patients notice new or worsening pain or the appearance of a new mass. Imaging tends to reveal aggressive findings, for example periosteal changes and new lucencies.
Because of the risk of transformation, some specialists recommend serial follow-up to ensure stability (e.g. 6-monthly) 1.
In this case, the appearance was deemed to be classic, one of the so-called "do-not-touch" lesions, and it was treated conservatively, as is often the approach decided upon.