Tracheal morphology in patients with tracheomalacia: prevalence of inspiratory lunate and expiratory "frown" shapes.
To identify the spectrum of tracheal morphologies in patients with tracheomalacia, and to determine the prevalence of specific inspiratory (lunate) and expiratory (frown) shapes that have been associated with this condition. A retrospective review was performed of a consecutive series of patients with bronchoscopically-proven tracheomalacia who were imaged with inspiratory and dynamic-expiratory computed tomography (CT). The CT images of each patient were reviewed in a blinded, randomized fashion by an experienced thoracic radiologist. For each case, the shape of the trachea at end-inspiration and dynamic expiration was classified using specific tracheal morphologies described in the literature. The study population included 17 patients, with a mean age of 54 years. At inspiration, 16 (94%) of 17 subjects demonstrated a normal tracheal configuration (round, oval, horseshoe, or inverted-pear shape), and 1 (6%) of 17 subjects demonstrated an abnormal "lunate" tracheal configuration (coronal: sagittal ratio >1). At expiration, 9 (53%) of 17 subjects demonstrated a crescenteric, "frown" shape; 1 (6%) subject demonstrated complete collapse; and 7 (41%) subjects demonstrated other morphologies. Inspiratory tracheal morphology is almost always normal in patients with tracheomalacia, with a lunate configuration only rarely observed. In contrast, an expiratory "frown sign" is observed in approximately half of patients with this condition. This sign has the potential to aid the detection of tracheomalacia when patients inadvertently breathe during routine CT scans.