The longitudinal folds are preserved parallel but very accentuated and somewhat “separated” in this pulmonary atelectasis by extrinsic compression. Recall that in the trachea only the malignant conditions contiguous to its posterior wall “accentuate and separate” their folds, while the compressions of nonmalignant causes produce the bulge of the wall and the folds can be separated but not accentuated or “sink” in the mucosa, because it is not infiltrated but has only been pushed towards the tracheal lumen.
