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Figure 2a.  Tracheal stenosis. (a) Posteroanterior and (b) lateral radiographs of the upper airways show narrowing of the tracheal lumen in the subglottic trachea (arrows). (c) Curvilinear coronal reformation of CT scan shows the narrowed segment (arrows) (1 = craniocaudal length of the stenosis, 2 = transverse diameter of the tracheal lumen at the stenosis). (d) Posteroanterior radiograph of the trachea in another patient, obtained with filtered high-kilovoltage technique, shows two tracheal narrowings (arrows).