What causes comet tail sign in the lung on chest imaging?
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The comet tail sign in the lung is caused by contracted fibrous scarring and shrinking of pleural disease, leading to the development of rounded atelectasis. This is commonly associated with asbestos-related pleural disease but may also occur with chronic pleural infections (e.g., tuberculosis), congestive heart failure, or pulmonary infarcts. The sign represents distortion and bending of the bronchovascular bundles adjacent to a subpleural mass or area of atelectasis.
Why is it called so?
It is named the “comet tail sign” because on imaging, especially CT, the affected area shows curvilinear soft tissue opacities (distorted blood vessels and bronchi) extending from the medial margin of a subpleural round mass or atelectatic lung toward the pulmonary hilum, resembling the shape of a comet’s tail.
Pathophysiology
Fibrous contraction and pleural thickening cause a subpleural lung region to collapse and fold on itself (rounded atelectasis). This folding drags and distorts the adjacent bronchi and pulmonary vessels, producing a curvilinear pattern pointing toward the hilum. This bronchovascular distortion on imaging appears as the tail, while the mass of atelectatic lung represents the comet’s head.
Alternative names: Rounded atelectasis (when referring to the underlying process)
Other associated named signs: Parachute sign (when multiple tail-like vessels are present converging on the atelectatic lung)
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