A tracheal bronchus (with some variations also known as a pig bronchus) is an anatomical variant where an accessory bronchus originates directly from the supracarinal trachea. The latter term (pig bronchus or bronchus suis) is often given when the entire upper lobe (usually right side) is supplied by this bronchus.

It is nearly always an incidental finding, as in this case.  It may be identified on bronchoscopy or CT.