True Tracheal Bronchus.

A 35-year-old male nonsmoker presented with complaints of left-sided dull aching chest pain and dry cough for 20 days. A chest radiograph showed a left hilar mass. Computed tomography of the chest showed a heterogenous mass in the hilar region involving the left main bronchus. On multiplanar reconstruction coronal images, an incidental finding of tracheal bronchus or "pig bronchus" (white arrow, Fig. 1A) was noted. Flexible bronchoscopy was performed to biopsy the mass lesion where an accessory bronchial opening (white arrow) at the right tracheal wall just prior to the main carina (black arrow) was seen (Fig. 1B). This tracheal bronchus was serving the right upper lobe and had normal apical, posterior, and anterior segments. It is also known as "pig bronchus" (bronchus suis) or "true tracheal bronchus." The right mainstem bronchus was the bronchus intermedius, which was further dividing into middle and lower lobe bronchi.