Peribronchial cuffing, also referred to as peribronchial thickening or bronchial wall thickening, is a radiologic sign which occurs when excess fluid or mucus buildup in the small airway passages of the lung causes localized patches of atelectasis. This causes the area around the bronchus to appear more prominent on an X-ray. It has also been described as donut sign, considering the edge is thicker, and the center contains air.