Hierarchical clock-scale hand-drawn mapping as a simple method for bronchoscopic navigation in peripheral pulmonary nodule

In this study, we have established a novel hierarchical clock-scale hand-drawn mapping method for bronchoscopic navigation, which could emerge as a simple, economical and feasible guiding modality for pulmonary nodule biopsy. The navigation mapping with ultra-thin bronchoscopy provided a more distal airway detection and a diagnostic yield of 75% for peripheral pulmonary lesion.

Peripheral pulmonary nodule, with an increasing prevalence, presents a particular challenge for tissue biopsy and accurate diagnosis. Bronchoscopic navigation systems (VBN, ENB, etc.) were recently implemented to guide transbronchial lung biopsy with a good diagnostic yield, but requiring high consumption and long training time [13, 14], which might limit the widely use of navigation method for lung biopsy in majority of general hospitals. A novel navigation modality with simple and fast preparation is currently required further exploration.

In the previous study, Prof. Noriaki Kurimoto had first introduced the bronchial branch tracing method for bronchoscopic diagnosis [11]. Subsequently, Zhang et al. reported a manual mapping method for guiding pulmonary nodule biopsy in the clinical practice [15]. Whereas, the manual mapping might be mainly based upon individual experience, lacking a standard operating procedure (SOP) and quantitative guideline for accurate navigation. Hence, in review of previously published research, we aimed to establish a normative approach of hierarchical clock-scale hand-drawn mapping for bronchoscopic navigation based on the “clock” scale, making it feasible for accurately guiding pulmonary lesions along with bronchial generations. Since bronchoscopists have various operation habits and standing positions, the SOP of navigation mapping would provide a standardized approach for guiding transbronchial lung biopsy.

The VBN system might have limitation in planning a pathway to the peripheral airways (generally less than 3 mm in diameter), which is associated with the finite resolution of CT imaging for detecting the sixth generation bronchi or more distal airways [16, 17]. Furthermore, CT measurement algorithm errors, airway structural variation and sputum blocking could commonly give rise to the deviation of planned path in navigation system. By contrast, the navigation mapping method is conducted on the basis of imaging reading by sophisticated operator, which could reduce the magnitude of limitation by CT image artifacts and airway luminal secretion. Taking this into account, it is therefore plausible that the bronchoscopic navigation mapping could provide an deep detection of the distal airways. Moreover, compared to VBN system, the navigation mapping method occupied markedly less time for planning a pathway along with bronchial generations and guiding to the target pulmonary lesion, making it feasible and simple to perform the bronchoscopic navigation with time-saving and easy preparation.

The preliminary clinical use of navigation system (VBN, ENB, etc.) with routine bronchoscope might confer a limitation for detecting peripheral pulmonary nodule in the more distal airways. Until fairly recently, the introduction of ultra-thin bronchoscope, with outside diameter of 3.0 mm, was reportedly conducive to access peripheral airways, expanding the bronchial inspection and improving the diagnostic yield of peripheral pulmonary lesions [7, 18, 19]. In the current study, HBN in conjunction with ultra-thin bronchoscope, accessing to the 7th generation or more distal airways, provided a diagnostic yield of 75% for peripheral pulmonary nodule, which was compatible with that of routine bronchoscopy with virtual navigation. This lent support to the possibility that HBN combined with ultra-thin bronchoscope could serve as a potential surrogate for virtual bronchoscopic navigation system in the majority of general hospitals with cost–benefit consideration.

Some caveats should be considered. The current study was conducted in a single medical center with small sample sizes, which might limit the generalizability of our findings. Secondly, we performed comparisons between VBN + routine bronchoscope and HBN + ultrathin bronchoscope, which was recently implemented in clinical practice, rather than using ultrathin bronchoscope in both groups, might have slightly biased the results. Whereas, it would not weaken the tenability of the conclusion that HBN provides an analogous value for guiding peripheral pulmonary nodule biopsy compared with VBN system.

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