Fig. 7.

Asymmetric osteopenia, misinterpreted as a lytic lesion when viewed at CT bone window settings. Axial CT scans of pelvis displayed at a bone and b soft tissue window settings. The asymmetric region of low attenuation in the right sacral ala (arrow) initially was suspected to represent metastasis of patient’s known bladder cancer. However, visual evaluation of the region on b soft tissue windows suggested the presence of fat throughout that region (arrowhead), which was proven by region-of-interest measurement (−52 Hounsfield units; normal fat = −50 to −100 HU)