ground-glass opacity

Ground-glass opacity (GGO) describes a hazy, slightly increased greyness in part of the lung on CT — like frosted bathroom glass that softens the view without blocking it. The crucial feature is that you can still see the lung's blood vessels and bronchial walls through the haze. That is what separates it from denser, solid-white consolidation, which hides the vessels behind it.

Physically, the haze means the air spaces are partly, not completely, filled or the surrounding tissue is mildly thickened — by a little fluid, inflammatory cells, blood, or early scarring — so X-rays are attenuated a bit more than in normal lung but not fully. It is a finding, not a diagnosis: many very different processes can produce the same hazy appearance.

Its meaning depends entirely on context. Diffuse ground-glass can reflect infection (including some viral pneumonias), inflammation, fluid overload or interstitial disease, while a small focal ground-glass nodule that persists may represent a slow-growing early adenocarcinoma. Doctors interpret GGO together with its distribution, how it changes over time, and the patient's clinical picture rather than in isolation.