Mach bands in mammography.

The radiologic appearance of tissue surrounding a tumor often influences the characterization of a cancerous lesion. An example is the radiolucent halo that is sometimes seen around breast cancers. Mammograms of 108 malignant tumors (74 scirrhous tumors, 17 partially scirrhous nodular tumors, and 17 nodular tumors) and eight benign tumors that showed peritumoral fat were retrospectively evaluated. All the scirrhous and partially scirrhous nodular cancers were more or less surrounded by a 5-10-mm-wide hyperlucent halo; this corona sign was also found in 14 nodular cancers. The halo sign, a hyperleucent 1-mm band, was observed around all benign lesions and immediately adjacent to sharply delineated cancers. These radiologic findings are an optical illusion (Mach band, background contrast effect). Densitometric measures and isoluminous analysis did not demonstrate the presence of a true hyperlucent zone.