Tracheal bronchus

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.

Terminology

The term (pig bronchus or bronchus suis) is often given when the entire upper lobe (usually right side) is supplied by this bronchus ⁵.

However, this term is used in some literature to encompass a wider spectrum of abnormalities including accessory bronchi originating from either the trachea or main bronchi.

Epidemiology

Incidence is estimated at ~1% (range 0.1-2%), and there is a marked right sided predilection ^1,2,5.

Clinical presentation

Often incidentally discovered and most patients are asymptomatic. Occasionally patients may have a recurrent (right) upper lobe pneumonia due to focal emphysematous change.

Pathology

Tracheal bronchi arise from the right lateral wall of the trachea usually at a distance of <2 cm from the level of the carina ⁵.

They can be classified into two main types:

• supernumerary: usual bronchial supply to affected lung segment is concurrently present

• displaced: usual bronchial supply to affected lung segment is concurrently absent

Radiographic features

CT

CT is the best modality for assessing the anatomy and allows direct visualisation and orientation of the anomalous bronchus. Coronal multi-planar reconstructions in "lung window" settings are the most helpful and is best in depicting this anomaly.

History and etymology

It was initially described by Sandifort in 1785 ².