Triangular Margin: Reliable Imaging Feature of Fibrous Dysplasia in Long Bones?

To determine the utility of a triangular margin as an imaging diagnostic feature for fibrous dysplasia.

We retrospectively reviewed all surgically biopsied or managed benign and malignant bone tumors by a single orthopedic oncologist over 19 years (2003 to 2022). A musculoskeletal radiologist and an orthopedic oncologist, both with >10 years of experience, retrospectively evaluated all imaging in consensus. Groups were compared using the χ 2 test.

There were a total of 152 subjects [mean age 49±21 (range 7.8 to 91) years]; 80 (53%) females and 72 (47%) males. There were 52 subjects with fibrous dysplasia, 31 subjects with other benign bone tumors, and 69 subjects with malignant bone tumors. The sensitivity and specificity of a triangular margin for distinguishing fibrous dysplasia from other benign or malignant bone tumors were 74% and 96% on radiographs, 73% and 100% on CT, and 78% and 91% on MRI, respectively. The triangular margin was more prevalent in fibrous dysplasia (85%) versus benign (16%) and malignant (1.6%) primary bone tumors in all 3 modalities ( P <0.001). Multivariate analysis of the aggregated imaging data suggests that if a lesion has a triangular margin, it is 14 times more likely to be a fibrous dysplasia than another benign bone tumor ( P =0.012).

The presence of a triangular margin could increase a radiologist's confidence that a bone tumor is fibrous dysplasia.