Computed tomography of the left retrobronchial stripe.

Posterior to the left hilum, lung contacts and outlines the posterior wall of the left main bronchus, producing a stripe of density (left retrobronchial stripe) visible using computed tomography. Thickening or nodularity of the stripe, resulting in separation of air in lung from air in the bronchial lumen often reflects tumor infiltration of the bronchial wall, or lymphadenopathy. Consolidation of the lower lobe can obliterate the stripe, but, because the pleural space does not extend posterior to the bronchial wall, pleural effusion generally will not.