Vertebral hemangiomas: fat content as a sign of aggressiveness. Thirty-two vertebral hemangiomas (VHs) were evaluated with nonenhanced computed tomography (CT), T1-weighted magnetic resonance (MR) imaging, CT enhanced with contrast material, and selective spinal arteriography. The stroma between the osseous trabeculae was found to correspond to either fatty tissue or soft tissue or both. All 11 asymptomatic VHs showed complete fatty stroma at CT and increased signal intensity at MR imaging. In contrast, all four compressive VHs had soft-tissue attenuation at CT. Three compressive VHs showed low signal intensity on MR images. Predominantly fatty stroma at CT and increased signal intensity at MR imaging were associated with normal or only slightly increased vascularization at selective spinal arteriography or contrast-enhanced CT, while soft-tissue stroma at CT and low signal intensity at MR imaging were associated with distinct hypervascularization. The authors' experience suggests that fatty VHs may represent inactive forms of VH, while soft-tissue content at CT and low signal intensity at MR imaging may indicate a more active vascular lesion with potential to compress the spinal cord. CT and MR imaging may be especially valuable for evaluating patients with clinical signs or symptoms of uncertain origin and findings compatible with VH at plain radiography. 