Letters to the Editor
To the Editor:
Lobar bronchi, also known as secondary bronchi, arise from the primary bronchi and serve as a specific lung lobe airway. The right main bronchus subdivides into 3 lobar bronchi. The right upper lobe orifice averages 10 mm and has many variations, the most common one is trifurcating into apical, posterior, and anterior segmental bronchi. It corresponds to the Boyden classification B1, B2, and B3 segmental bronchi.1 Each of these endup subdividing to supply 2 bronchopulmonary subsegments.
Variations in the airways are believed to be the result of developmental disturbances of the lungs, such that an inappropriate number of lung buds develop or arise at atypical sites. Most bronchial anomalies are on the right, and a tracheal bronchus and supernumerary superior segmental bronchus are among the most common findings.2
Occasionally, an extra bronchus supplies the lateral aspect of the right upper lobe. This axillary bronchus is usually a subsegmental bronchus, but may arise as a segmental branch. When segmental, the axillary bronchus most often originates adjacent to the posterior bronchus. Rarely, an axillary segment can also be present on the left.
Foster-Carter have reported this fourth segmental bronchus arising from the right upper lobe bronchus and supplying an “axillary” segment in approximately 10% of cases.3 Other authors describe instead a “quadrivial type of branching” occurring in 5.3% to 16% of cases.1,4–6
In these cases, if it is a segmental bronchus, the axillary bronchus most often originates adjacent to the posterior bronchus.
Airspace disease in the axillary subsegment has a characteristic appearance on radiologic studies. Awareness of this variant anatomy may explain an otherwise confusing finding, and can help in obtaining samples. These images were obtained from surveillance bronchoscopies and depict the presence of the axillary segment (Figs. 1–3).
Diego I. Conci, MD
Cleveland Clinic Foundation, Beachwood, OH
1. Boyden EA, Scannell JG.An analysis of variations in the bronchovascular pattern of the right upper lobe of fifty lungs.Am J Anat.1948;82:27–64.
2. Atwell SW.Major anomalies of the tracheobronchial tree with a list of the minor anomalies.Dis Chest.1967;52:611–615.
3. Foster-Carter AF.The anatomy ofthe bronchial tree.Br J Tuberc.1942;36:19–38.
4. Yamashita H.Roentgenologic Anatomy of the Lungs.1978.Tokyo:Igaku-Shoin Ltd;70–72.
5. Scanneil JG, Boyden EA.A study of variations of the bronchopulmonary segments of the right upper lobe.J Thorac Surg.1948;17:232–237.
6. Brock RC.The Anatomy of the Bronchial Tree.1946.London:Oxford University Press;37–65.