Diffusion-weighted magnetic resonance imaging of sacral insufficiency fractures: comparison with metastases of the sacrum

Retrospective analysis of magnetic resonance imaging (MRI) for differentiating sacral insufficiency fractures from metastases of the sacrum. To determine if a steady-state free precession (SSFP) diffusion-weighted MRI is useful for differentiating sacral insufficiency fractures from metastases of the sacrum. Conventional spin-echo sequence MRI is very sensitive for the detection of pathologic lesions in the sacrum, but the differential findings between sacral insufficiency fracture and metastasis are often not obvious because of the nonspecific changes of signal intensity. Another MR sequences for differentiation is needed. Fourteen patients with sacral insufficiency fractures and 8 patients with metastasis at the sacrum were examined with MRI. Both the diffusion-weighted MRI and the spin-echo MRI were performed in all patients. Diffusion-weighted MRI sequences were based on a SSFP sequence. All the insufficiency fractures and metastasis at the sacrum revealed low signal intensity on T1-weighted MRI; low or high signal intensity was revealed on T2-weighted MRI. The contrast enhanced T1-weighted MRI showed strong enhancement at the sacrum in all cases of insufficiency fracture and metastasis. Diffusion-weighted MRI of the sacrum showed low signal intensity in all cases with sacral insufficiency fracture, but these images revealed high signal intensity in all cases with metastasis. SSFP diffusion-weighted MRI is capable of differentiating benign sacral insufficiency fractures from metastatic tumors of the sacrum.