Bull's-eyes and halos: useful MR discriminators of osseous metastases.

To evaluate the presence of (a) a focus of high signal intensity in the center of an osseous lesion (bull's-eye) as a negative discriminator for metastasis and (b) a rim of high signal intensity around an osseous lesion (halo) as a positive discriminator, a retrospective study was performed in 47 patients with osseous lesions suspect for metastatic disease who underwent magnetic resonance (MR) imaging of the pelvis. The findings in 17 patients with proved osseous metastasis were compared with those in 30 patients not believed to have metastatic disease; T1- and T2-weighted MR images were evaluated. The bull's-eye sign was found to be a specific indicator of normal hematopoietic marrow (sensitivity, 95%; specificity, 99.5%). The halo sign and diffuse signal hyperintensity were a strong indicator of metastatic disease (sensitivity, 75%; specificity, 99.5%). These results suggest that use of the bull's-eye sign as a discriminator of benign disease and use of the halo sign as a discriminator of metastasis help characterize suspect areas of marrow lesions.