AJR:197, December 2011
Carole A. Ridge Alexander A. Bankier Ronald L. Eisenberg
Mosaic attenuation is a CT pattern defined by the Fleischner Society glossary as a "patchwork of regions of differing attenuation seen on CT of the lungs." It is characterized by heterogeneous lung attenuation with well-defined borders cor- responding to the secondary pulmonary lobules. The name derives from mosaic artwork, which consists of variously colored glass or stone tiles inlaid in a contrasting pattern (Fig. 1). The three major pathologic causes of this pattern are pulmonary vascular, small airways, and primary parenchymal disease. These entities can be differentiated on CT by correlating inspiratory with expiratory images and evaluating the appearance of the pulmo¬nary vasculature The mosaic pattern can be explained by a nonuniform distribution of disease. In pulmo¬nary vascular disease, hypoperfused lung appears lower in attenuation than adjacent normal or hyperperfused lung. Similarly, in small airways disease, regional variations in the presence of air trapping lead to a patchwork of low-attenuation lung that is interposed with normally ventilated higher-attenuation lung. Conversely, in primary parenchymal disease, the higher-attenuation lung is abnormal and, when heterogeneously distributed, contrasts with adjacent normal lower-attenuation lung to produce a patchwork mosaic pattern.