High resolution computed tomography of the lungs: ground glass opacity and its differential diagnosis

Ground glass opacity (GGO) is defined as diffuse pulmonary infiltration which does not obscure vessels and bronchial walls and is due to intra-alveolar or interstitial processes of pulmonary parenchyma which only partially replace air. The etiology is variable including edema, airspace and interstitial pneumonia due to different organisms, non-infectious pneumonitis as well as tumor manifestations. Physiological processes, such as poor ventilation of dependent lung areas and effects of expiration can also present as ground glass opacity.This review describes the physiology and pathophysiology of GGO, illustrates different examples of common diseases presenting with GGO and reviews how GGO may be used for diagnosis and differential diagnosis of pulmonary disease.