What causes the comet tail sign in the chest on CT imaging?
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The comet tail sign in the chest is caused by the presence of round atelectasis, a form of focal lung collapse adjacent to chronic pleural disease, usually manifesting as pleural thickening or fibrosis. On CT imaging, this sign results from distortion and curvilinear convergence of bronchovascular bundles that are pulled into the atelectatic mass. This finding is associated with underlying pathologies such as asbestos exposure, prior pleuritis, or pulmonary fibrosis.
Why is it called so?
It is named the “comet tail sign” because the curved bronchovascular bundles extending from the subpleural round atelectasis toward the hilum resemble a comet’s tail trailing from its head, creating an image akin to a comet streaking through the lung parenchyma on chest CT.
Pathophysiology
The sign develops due to focal peripheral lung collapse (round atelectasis) secondary to pleural thickening or fibrosis. The adjacent pleura contracts, tethering contiguous vessels and bronchi and pulling them into a curvilinear, tapering configuration that extends toward the lung hilum. This bronchovascular distortion within the lung parenchyma produces the characteristic tail-like appearance of the comet tail sign on imaging.
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