Tracheal Bronchus

A tracheal bronchus is an aberrant bronchus that arises from the trachea directly. It is seen normally in swine, cattle, sheep, goats, camels, giraffes, and whales. In humans, it is an anatomic variant that can be associated with other bronchopulmonary anomalies, tracheal stenosis, or Down syndrome. While usually asymptomatic, a tracheal bronchus is occasionally the etiology for chronic pulmonary disease such as emphysema, bronchiectasis, atelectasis, and persistent or recurrent pneumonia. A tracheal bronchus should be considered in intubated patients with right upper lobe complications.

A tracheal bronchus usually arises from the right lateral wall of the trachea less than 2 cm above the carina. It can supply only the apical segment or the entire upper lobe. A right tracheal bronchus has a prevalence of 0.1%–2%, while a left tracheal bronchus a prevalence of 0.3%–1%.

Analogous to the replaced/accessory terminology in variant hepatic arterial supply, a tracheal bronchus can be displaced or supernumerary. A displaced (not replaced) right tracheal bronchus is more common and arises from the trachea in the setting of an absent apical branch of the anatomic right upper lobe bronchus. A supernumerary (not accessory) right tracheal bronchus exists in the setting of a normal trifurcation of the right upper lobe bronchus.

Since its original description as a right upper lobe bronchus originating from the trachea, the term tracheal bronchus has been confusingly expanded to include origins from the carina and even mainstem and distal bronchi. These may be properly referred to as ectopic bronchi, reserving the term tracheal bronchi for the subset that arise from the trachea.

A nomenclature has been proposed using terms like eparterial, hyparterial, preeparterial, posteparterial, prehyparterial, and posthyparterial that vary depending on which side we're talking about. Those interested in the terminology can refer to the excellent review by Ghaye and colleagues.

References

• Berrocal T, Madrid C, Novo S, Gutiérrez J, Arjonilla A, Gómez-León N. Congenital anomalies of the tracheobronchial tree, lung, and mediastinum: embryology, radiology, and pathology. Radiographics. 2004 Jan-Feb;24(1):e17.
• Ghaye B, Szapiro D, Fanchamps JM, Dondelinger RF. Congenital bronchial abnormalities revisited. Radiographics. 2001 Jan-Feb;21(1):105-19.
• Ritsema GH. Ectopic right bronchus: indication for bronchography. AJR Am J Roentgenol. 1983 Apr;140(4):671-4.