In our study, there was a significant association between TBB obtained from left upper lobe and development of post-procedure pneumothorax. Our results are consistent with the study previously published by Herout et al., which also found a significantly higher risk of pneumothorax in the left upper lobe (1). Interestingly, in both studies there was also a trend towards increased risk of pneumothorax following TBB from the right upper lobe, however, this was not found to be statistically significant. Additionally, in a study by Huang et al, 10 out of 13 post-TBB pneumothoraces occurred from biopsy of the upper lobes, although this study was not adequately powered to show a significant difference between lobes.
The rationale for the increased risk of pneumothorax post TBB obtained from the upper lobes is not well understood. Subpleural blebs and emphysema are more prominent in the upper lobes, which may predispose to pneumothorax if inadvertently biopsied. In addition, alveoli at the apices of the lung are more distended and less compliant than the bases because of the pleural pressure gradient9. The effect of gravity and the weight of the lung may also play a role; a tear in the dependent visceral pleura may be sealed due to the weight of the lung, particularly when the patient remains upright after the procedure If a defect occurs in the apical lung, the weight of the lung may promote recoil away from the chest wall, causing a pneumothorax to accumulate. The true mechanism for this phenomenon however remains uncertain.
It is also unclear why there are differences in pneumothorax between the right and left upper lobes. The anatomy of the bronchial tree may provide a possible explanation. In the left upper lobe, the apical-posterior and anterior segments branch at a broad angle in relation to the lingula. A pneumothorax in the apical-posterior or anterior segments could promote recoil downward and laterally towards the lingular segment. For comparison, in the right upper lobe, only the apical segment exits at a broad angle and would have the tendency to recoil downward. In addition, difficulty in correctly judging the appropriate depth of biopsy in the apical-posterior segment of the left upper lobe may explain why there is an increase in risk of pneumothorax, although this is purely speculative.
We found that the patients admitted to hospital at the time of their procedure had a higher risk of pneumothorax which is a novel finding not previously reported. More severe underlying lung disease as well as acute presentations of lung disease are inherent to the inpatient population and may account for this finding. Previous studies that examined the rates of complications from bronchoscopy in the outpatient setting often reported lower rates than that in the inpatient setting13,15. Clinicians should be aware of this increased risk and take it into consideration when determining if to proceed with TBB for their inpatient population.
The incidence of pneumothorax in our study is higher than most previously published studies1,5,10,12. One reason to explain this discrepancy may be related to the outcome used in our study of radiologist reported pneumothorax. Seven of the pneumothoraces included were reported as questionable and were of no clinical significance. Moreover, others were small and clinically insignificant. Only 4.5% of individuals developed pneumothorax that required intervention with a chest tube which is consistent with the established incidence of 1–6%5,12. Additionally, 24 patients were not included in the analysis as they did not have a post-procedure chest x-ray. It is unlikely these individuals had a symptomatic pneumothorax given lack of imaging requirement. As such, the 17% risk of pneumothorax may be an overestimate due to lack of inclusion of these individuals. Lastly, operator experience may influence the complication rate. Our study was conducted at a teaching center with differing levels of operator experience. In a large single-cohort study, Yeow et al. reported operator experience as the third major risk factor for pneumothorax in CT guided lung biopsies11, although this has not been reliably found to be associated with increased risk of pneumothorax8,14.
In conclusion, our study found that the risk of pneumothorax was highest when TBB was performed from the left upper lobe. Clinicians should be aware of this increased risk and take it into consideration when determining preferred location of biopsy for individuals with diffuse lung disease. Further evidence, ideally a prospective multi-centre study, is needed to confirm this finding.