| Discussion: |
Mosaic attenuation of lung on CT can be grouped into three categories:
Small airways disease: Regional air trapping and hypoxic vasoconstriction will appear as decreased size and number of vessels and decreased attenuation in the affected regions in comparison to areas of normally ventilated lung. Decreased attenuation and/or increased volume of affected areas will persist on end-expiratory images. The differential includes asthma, bronchiolitis obliterans, cystic fibrosis.
Small vessel disease: Also known as “mosaic perfusion”, obliteration of small vessels gives the affected areas a decreased attenuation in comparison to normally perfused lung. There will be no air trapping on end-expiratory images. The differential includes chronic pulmonary embolism.
Infiltrative disease: Patchy infiltration of the interstitium and/or partial filling of airspaces with fluid, cells, or fibrosis will increase attenuation in affected areas. The vessel size will be uniform and there will be no air trapping. The differential includes Pneumocystis carinii pneumonia, eosinophillic pneumonia, hypersensitivity pneumonia.