Mosaic Perfusion or Mosaic Lung Sign

Mosaic perfusion (mosaic attenuation, the “mosaic lung” sign) refers to areas of decreased attenuation of lung parenchyma (↑) in the regions of reduced blood perfusion. The term “mosaic” reflects patchy distribution of abnormalities. This sign is usually seen in patients with small airways diseases (cystic fibrosis, bronchiolitis obliterans, and chronic obstructive lung disease) and pulmonary vascular disease (mosaic oligemia in chronic pulmonary embolism). In cases with mosaic perfusion, regional pulmonary artery branches are always reduced in size. This pattern gives opportunity to distinguish mosaic perfusion from ground-glass opacities.