Low-attenuation mediastinal masses on CT

A variety of mediastinal masses contain areas with CT attenuation values lower than that of chest wall musculature and higher than that of subcutaneous fat, and, therefore, these areas appear cystic on CT. In some cases, the low attenuation is not absolute but is relative to an enhancing wall of the lesion or to surrounding structures on contrast-enhanced CT images. In these cases, precise determination of the attenuation values discloses a density equivalent to that of soft tissue. In this report the gamut of low-attenuation mediastinal masses seen on CT is illustrated.