Background: The nodular bronchiectatic (NB) form of non-tuberculous mycobacteria (NTM) lung disease usually involves the right middle lobe (RML) and the left upper lobe lingular segment. However, the reason underlying this preference is not known.
Methods: Fifty patients with NB NTM lung disease who had both positive NTM culture(s) and NB lesions in the RML or lingular segment on computed tomography (CT) of the chest, and 100 healthy subjects matched for sex, age, height and body weight with normal chest CT, were randomly selected. Using reconstructed curved multiplanar reformation (MPR) images, the lengths, diameters and angles of the RML and lingular bronchi were measured.
Results: Of the 150 individuals, 64% were female; the mean age was 55 years. The angles of the bronchi were significantly more acute in patients than in healthy subjects, both in the RML (patients, mean 46.75° ± standard deviation 8.87° vs. healthy subjects, mean 51.73° ± 7.76°; P = 0.001) and in the lingular segments (patients, mean 26.94° ± 8.16° vs. healthy subjects, mean 34.65° ± 9.75°; P < 0.001). In addition, the angles of the bronchi in the involved segments were more acute than those in the non-involved segments, both in the RML and the lingular segments. There were no differences in the lengths and bronchi diameters between groups.
Conclusions: An acute angle (obtuse slope) of RML/lingular bronchi could be an anatomical risk factor for NB NTM lung disease.