Imaging differentiation of pathologic fractures caused by primary and secondary bone tumors

Objective: To describe pre-treatment imaging features of pathologic fractures caused by primary bone tumors (PBTs) and metastatic bone tumors (MBTs) and determine if radiographic or cross-sectional features can differentiate the underlying pathologies associated with the fractures. Methods: Sixty-nine patients with a diagnosis of a pathologic fracture were enrolled. Biopsy established PBT as the cause of the pathologic fracture in 16 (23%) cases and MBT in 53 (77%) cases. The radiographs, computed tomography (CT) scans, and magnetic resonance imaging (MRI) scans of the subjects were retrospectively reviewed for the presence of multiple imaging features. Results: Compared to pathologic fractures caused by MBTs, the fractures caused by PBTs demonstrated a higher incidence of lytic bone cortex, mineralization and a soft-tissue mass on radiographs, mineralization and a soft-tissue mass on CT scans, and periosteal abnormality on MRI scans (P < 0.01). These features also exhibited a high negative predictive value in supporting the diagnosis of an underlying PBT over MBT. Conclusion: Pathologic fractures caused by PBT and MBT may be differentiated by a few specific radiographic and CT imaging features, though MRI was poor for characterization of the underlying lesion. Such knowledge may assist radiologists in raising the possibility of a PBT as the cause of a pathologic fracture.