Ground-glass opacity: interpretation of high resolution CT findings

Ground-glass opacity (GGO) is a common finding on high resolution CT, characterised by areas of hazy increased attenuation of the lung with preservation of bronchial and vascular margins; it is not to be confused with consolidation, in which bronchovascular structures are obscured. It correlates with several pathogenic processes, such as like partial filling of air spaces, inflammatory or fibrotic interstitial thickening, increased capillary blood volume. Infiltrative GGO can representing either interstitial or alveolar processes. GGO is a nonspecific finding; however, the correlation with any of the associated CT findings (nodular lesions, consolidation, septal thickening, fibrosis, vessels or airway calibre alterations, air trapping), and clinical data is helpful in narrowing the range of diagnostic possibilities, or even in suggesting a specific diagnosis. GGO can indicate a potentially treatable disease, help guide the type and location of biopsy and evaluate the effectiveness of therapy. This review discusses the types of lung disease associated with GGO, and the differential diagnosis between GGO caused by infiltrative processes and the mosaic patterns of lung attenuation caused by primary vascular diseases or airway abnormalities. This distinction can be made by evaluating the vessel calibre and air trapping on expiratory scans.