The dark bronchus sign is the appearance of a relatively darker bronchus as compared to adjacent ground glass opacity. Normally, the density of lung parenchyma and the bronchiolar lumen is similar. In cases of ground glass opacity, the bronchiolar lumen within the affected lung parenchyma appears relatively darker and helps to discern even subtle or diffuse ground glass opacification. If the ground glass opacity progresses to consolidation, air bronchograms will be visualized.
This sign is useful to identify diffuse ground glass opacity on HRCT chest in cases of Pneumocystis jirovecii pneumonia that may present with a normal or equivocal chest radiograph in the early course of the disease 1,4.
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- 5. Ayub II, Manimaran N, Sundaram S. Dark bronchus sign: a subtle indication of diffuse alveolar haemorrhage. (2019) BMJ case reports. doi:10.1136/bcr-2019-230991 - Pubmed