The branching patterns of bronchi and pulmonary arteries are associated with lingula division volume

Introduction

Lung segments can be defined as regions of the lung delineated by the branching of the bronchial tree. Each segment comprises its own segmental bronchus, accompanying pulmonary artery, and pulmonary veins. The segmental bronchi play a central role in the naming of lung segments. The anatomical structure of lung segments was first described by Appleton (1) and Boyden (2) in 1944 and 1945, respectively. In 1950, a nomenclature for bronchial anatomy was published (3). High quality and precise lung segment anatomical structure was beneficial for the completion of sublobectomy surgery (4).

Given the increasing number of segmental resections, there is a growing need for more detailed anatomical knowledge of lung segments (5,6). The lingula is a classic lung segment of the left upper lobe. Due to the singular intersegmental plane between the lingula and the adjacent segments, the technique for lingula segmentectomy is not technically complex. Thus, lingula segmentectomy is considered a relatively simple segmentectomy, and the anatomy of the lingula is often considered straightforward (7). However, in clinical practice, we have frequently observed anatomical variations in the lingula, which are more complex than previously assumed, and many rare variants have not been extensively reported.

The lingula segment bronchi are typically classified into two main branches: the upper lingula bronchus (B4) and the lower lingula bronchus (B5). However, not all specimens exhibit the typical division into one upper and one lower bronchus; in a few cases, the bronchial distribution resembles the right middle lobe, where the bronchus divides into two branches at the same level, which then course medially (B5) and laterally (B4) in the left upper lobe lingula (8). As observed in clinical practice, the lingula may have a longitudinal or transverse distribution, which may be related to the positional relationship between B4 and B5. Similarly, when the positional relationship between B4a and B4b changes, S4a and S4b may have either a vertical or horizontal relationship; likewise, when the positional relationship between B5a and B5b changes, S5a and S5b may also have either a vertical or horizontal relationship.

As the number of segmentectomies has increased, the lingula has garnered more attention from thoracic surgeons. In our clinical practice, we found that the anatomical characteristics of the lingula differ from those previously reported. A systematic review of the literature revealed that studies on the bronchial models of the lingula remain scarce, and detailed statistical analyses and classifications of the anatomical features of the lingula’s subsegments have rarely been performed (7-9). With advances in radiological imaging technology, three-dimensional (3D) computed tomography (CT) imaging has been shown to accurately visualize human anatomical structures, including those of the lungs (10). This has led to significant developments in thoracic surgeons’ understanding of the anatomical structure of lung segments. In this study, we conducted a large-sample, single-center study using 3D CT to systematically and comprehensively describe the bronchial and vascular anatomical features of the lingula. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-510/rc).

Methods

Clinical data

A retrospective analysis was performed of the chest thin-slice CT data of inpatients and outpatients at the Department of Thoracic Surgery, Yichang Central People’s Hospital, from January 2019 to June 2024. To be eligible for inclusion in the study, the patients had to meet the following inclusion criteria: (I) have CT scans in which the bronchial structures were clearly visualized; (II) have CT scans showing the natural shape of the bronchial tree, without respiratory motion artifacts. Patients were excluded from the study if they met any of the following exclusion criteria: (I) had a history of left lung resection; (II) had a congenital bronchial malformation; and/or (III) had severe organic lesions in the left upper lobe. A total of 4,862 imaging datasets, from 2,533 male and 2,329 female patients, were included in the study. The clinical data of these patients were analyzed to explore the types of bronchial branching in the lingula, and to perform a statistical analysis of the incidence and anatomical features of various subtypes. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The protocol of this study was approved by the institutional review board of Yichang Central People’s Hospital (No. 2023-190-01) and individual consent for this retrospective analysis was waived.

3D image reconstruction

Thin-slice spiral CT with a slice thickness of 0.625–2 mm was used to acquire medical digital imaging and communications in medicine (DICOM) data. The DICOM data were stored on dedicated servers. Volume rendering methods were employed to extract the anatomical structures of the lung (including the bronchi, pulmonary arteries, and pulmonary veins) from selected two-dimensional CT data, and 3D reconstruction was performed using the authorized software MIMICS (developed by Materialise Nv Co., Materialise’s interactive medical image control system, Belgium; serial number: A51D56D6-C3XE-0011-1F7605D216DF39D5). This study focused on the anatomical features of the left upper lobe lingula. All 3D images were analyzed and recorded by an experienced thoracic surgeon (perform over 300 surgeries annually) and an experienced radiologist (Work experience greater than 15 years). When there was a discrepancy between their findings, a senior thoracic surgeon performed arbitration. In our clinical practice, we compared the bronchial and pulmonary vascular anatomy seen in the 3D reconstructions with intraoperative findings, and found that 3D reconstruction was a reliable method for visualizing anatomical structures (Figure 1).

Figure 1 Three-dimensional interactive quantitative surgical planning of lingula segmentectomy. (A,B) Multidetector-row computed tomography images. (C-E) Three-dimensional computed tomography angiography and bronchography. (E) Three-dimensional computed tomography displaying the positional relationship of LS4+5. (F) The real situation of bronchi and pulmonary vessels during LS4+5 segmentectomy. The intraoperative findings were consistent with the preoperative 3D reconstruction.

Lingula and lingula bronchi

The bronchus of the left upper lobe lingula can have either a two-branch or three-branch type. The two-branch type can be further divided into two subtypes, of which the B4-B5 subtype has the most common anatomical configuration. This study primarily focused on the B4-B5 type. The B4-B5 type can be further classified as vertical (Type I) or horizontal (Type II) based on the positional relationship between B4 and B5 (Figure 2). B4 can be divided into lateral (B4a) and medial (B4b) branches, and B5 can be divided into superior (B5a) and inferior (B5b) branches. The positional relationship between B4a and B4b can be vertical or horizontal, as can that of B5a and B5b. We define the region of the lingular segment and its sub-segments through inter-segmental veins and inter-subsegmental veins. V3b is the inter-segment vein between anterior segment of left upper lobe and lingular segment, and it travels between S3b and S4b. V4a is the inter-subsegmental vein between S4a and S4b, and it travels between S4a and S4b. V4b is the inter segmental vein between S4 and S5, and it travels between S4b and S5a. V5a is the inter-subsegmental vein between S5a and S5b, and it travels between S5a and S5b.

Figure 2 The two patterns of LS4 and LS5. (A-C) Type I. (A) Superiorly and inferiorly bifurcated lingular segment bronchi. (B) Three-dimensional schematic of the vertical pattern. (C) Intraoperative observations of the vertical pattern. (D-F) Type II. (D) Horizontally bifurcated lingular segment bronchi. (E) Three-dimensional schematic of the horizontal pattern. (F) Intraoperative observations of the horizontal pattern. LLL, left lower lobe.

Positional relationships

A vertical relationship refers to two bronchial branches on the same vertical plane, with a lateral offset range of 45°. A horizontal relationship refers to two bronchial branches on the same horizontal plane, with an offset of 45° vertically. In Figure 3, the green range in the figure represents the horizontal relationship, while the purple range represents the vertical relationship. Thus, the B4-B5 type lingula bronchus has eight subtypes (see Figure 4). The positional relationship between S4 and S5 can be vertical or horizontal, depending on the positional relationship of B4 and B5. Similarly, the relationship between S4a and S4b, and S5a and S5b can be either vertical or horizontal (Figure 5).

Figure 3 The positional relationship of the bronchi. (A) The lingular segment bronchi; (B) the positional relationship between B4a and B4b; (C) the green range in the figure represents the horizontal relationship, while the purple range represents the vertical relationship.

Figure 4 Branch patterns of the lingular segment bronchi. (A-D) Type I: superiorly and inferiorly bifurcated lingular segment bronchi. (A) I-a: horizontally bifurcated superior lingular segment bronchi, superiorly and inferiorly bifurcated inferior lingular segment bronchi; (B) I-b: horizontally bifurcated superior lingular segment bronchi, horizontally bifurcated inferior lingular segment bronchi; (C) I-c: superiorly and inferiorly bifurcated superior lingular segment bronchi, superiorly and inferiorly bifurcated inferior lingular segment bronchi; (D) I-d: superiorly and inferiorly bifurcated superior lingular segment bronchi, horizontally bifurcated inferior lingular segment bronchi. (E-H) Type II: horizontally bifurcated lingular segment bronchi. (E) II-a: horizontally bifurcated superior lingular segment bronchi, superiorly and inferiorly bifurcated inferior lingular segment bronchi; (F) II-b: horizontally bifurcated superior lingular segment bronchi, horizontally bifurcated inferior lingular segment bronchi; (G) II-c: superiorly and inferiorly bifurcated superior lingular segment bronchi, superiorly and inferiorly bifurcated inferior lingular segment bronchi; (H) II-d: superiorly and inferiorly bifurcated superior lingular segment bronchi, horizontally bifurcated inferior lingular segment bronchi.

Figure 5 The positional relationship between S4 and S5 may be vertical (Type I) (A-D) or horizontal (Type II) (E-H). The relationship between S4a and S4b, and S5a and S5b, may be either vertical or horizontal.

3D image validation

In our clinical practice, we compared the bronchial and pulmonary vascular anatomy in 3D reconstructions with intraoperative findings, and found that 3D reconstruction is a reliable method for visualizing anatomical structures. We used 3D reconstruction to perform the statistical analysis of the anatomical features of the lingula and explored the relationship between different bronchial types of the lingula and lingula volume, as well as the relationship between different arterial types of the lingula and lingula volume.

Statistical analysis

The data were analyzed using SPSS 25.0 statistical software. The count data are expressed as the frequency and percentage. The consistency of observations between the two observers was assessed using the Kappa value; a Kappa value >0.80 indicated good consistency, a Kappa value between 0.60 and 0.80 indicated moderate consistency, a Kappa value between 0.40 and 0.60 indicated poor consistency, and a Kappa value ≤0.40 indicated poor agreement.

Results

A total of 4,862 imaging datasets, from 2,533 male patients (52.10%) and 2,329 female patients (47.90%) were included in the study. The age of the patients ranged from 34 to 79 years (57.83±5.21 years). Bronchial patterns of the left upper lobe lingula revealed two types: the two-branch type (4,731 cases, 97.31%) and the three-branch type (131 cases, 2.69%). Among the two-branch types, two subtypes were identified, of which the B4-B5 type had the most common anatomical pattern (4,692 cases, 96.5%, P<0.001), while the non-B4-B5 types (B4a-B4b+B5 type and B4+B5a-B5b type) were observed in 39 cases (0.8%) (Table 1).

Based on its positional relationship, the B4-B5 type can be classified as follows: vertical (Type I), and horizontal (Type II). Of the patients, 4,276 (91.13%) had Type I, while 416 (8.87%) had Type II. The incidence of Type I was significantly higher than that of Type II (P<0.001). For Type I, 4,021 cases (85.70%) had Type I-a, 109 (2.32%) had Type I-b, 90 (1.92%) had Type I-c, and 56 (1.19%) had Type I-d. In relation to Type II, 182 cases (3.88%) had Type II-a, 71 (1.51%) had Type II-b, 132 (2.81%) had Type II-c, and 31 (0.66%) had Type II-d. Type I-a was the most common type, while Type II-d had the lowest incidence (P=0.007) (Table 2).

In terms of the arterial pattern of the B4-B5 type lingula, 3,186 cases (67.90%) had the interlobar type, 865 cases (18.44%) had the mediastinal type only, and 641 cases (13.66%) had the mediastinal combined with interlobar type. The incidence of the mediastinal type was 32.10% (Figure 6A-6C). In terms of the venous pattern of the B4-B5 type lingula, there were 2,324 cases (49.53%) of one-branch type, and 1,862 cases (39.68%) of two-branch type, of which, 714 cases (15.22%) showed V4 and V5, 547 cases (11.66%) showed V4 + V5b and V5a, 333 cases (7.10%) showed V4a and V4b + V5, and 268 cases (5.71%) showed V4a+V5a and V4b+V5b. The three-branch type was observed in 506 cases (10.78%), of which 126 (2.69%) showed V4, V5a, and V5b, and 380 (8.10%) showed V4a, V4b + V5b, and V5a (Figure 6D-6F). The one-branch type was significantly more common than the other types (P=0.043) (Table 3).

Figure 6 Branching patterns of the lingular segmental artery and vein in the left upper lobe. (A-C) Branching patterns of the lingular segmental artery in the left upper lobe: (A) interlobar type; (B) mediastinal type; (C) mediastinal combined with interlobar type. (D-F) Branching patterns of the lingular segmental vein in the left upper lobe: (D) one-branch type; (E) two-branch type; (F) three-branch type.

In this study, we analyzed the characteristics of the patients in the Type I and Type II groups, and found no significant differences between the two groups in terms of age, gender, smoking history, body mass index (BMI), chest-to-abdomen ratio, chronic disease history, or pulmonary function [forced expiratory volume in 1 second (FEV1), percentile forced expiratory volume in 1 second (%FEV1), FEV1/forced vital capacity (FVC), and percentile diffusing capacity of carbon monoxide (%DLCO)] (Table 4).

There was no significant difference between the Type I and Type II groups in terms of the B4+5 diameter (6.17±0.68 vs. 6.21±0.73 mm, P=0.58). The B4 diameter was significantly larger in the Type I group than the Type II group (4.39±0.81 vs. 3.31±0.37 mm, P<0.001), but there was no significant difference in the B5 diameter between the Type I and Type II groups (3.17±0.53 vs. 3.09±0.77 mm, P=0.64). The lingula volume was significantly larger in the Type I group than the Type II group (330.48±84.17 vs. 280.76±56.22 mL, P=0.01). Compared to the Type II group, the Type I group had a significantly larger lingula volume/total lung volume (8.25%±0.93% vs. 7.30%±1.41%, P<0.001), lingula volume/left lung volume (17.82%±2.19% vs. 14.23%±2.05%, P<0.001), and lingula volume/left upper lung volume (34.93%±2.07% vs. 27.59%±2.22%, P<0.001). The lingula volume of the mediastinal type group (which included the mediastinal type only and the mediastinal combined with interlobar type) was larger than that of the interlobar type group (386.81±37.75 vs. 307.63±67.91 mL, P=0.009). Compared with the interlobar type group, the mediastinal type group had a significantly larger lingula volume/total lung volume (8.96%±1.33% vs. 7.93%±1.07%, P<0.001), lingula volume/left lung volume (19.73%±1.57% vs. 16.96%±2.39%, P<0.001), and lingula volume/left upper lung volume (37.33%±2.65% vs. 31.86%±3.87%, P<0.001) (Table 5).

Discussion

With the advancement of the Japan Clinical Oncology Group (JCOG) 0802 and 0804 studies (11-13), more and more scholars have recognized the advantages of sub-lobar resection in preserving lung function. Anatomical segmentectomy has become an important treatment for early stage non-small cell lung cancer; however, it is not a simple technique. Any surgeon using this technique needs to have a thorough understanding of the anatomical structures of the lung segments and the necessary skills to perform the procedure. The lingula segment is a classic lung segment, and due to the single intersegmental plane between the lingula segment and the inherent segment, the technique for its resection is not complicated. Thus, lingula segmentectomy is classified as a simple lung segment resection, which has led many to believe that the anatomy of the lingula segment is relatively simple (10,14,15). As a result, research on lingula segmentectomy has seldom been reported (16,17), and relevant anatomical studies on the lingula segment are also scarce. To our knowledge, this study represents the most extensive series of lingula segment studies in the world, and it was the first time our newly proposed nomenclature has been put into practice and systematically described.

In clinical practice, we have observed that the anatomy of the lingula is quite complex; it is a lung segment characterized as “simple to operate on, but complex anatomically”. Consistent with a previous report (9), after carefully studying the individual anatomical differences of 4,862 patients, we found that the bronchial structure of the left upper lobe lingula can be classified into the following two types: the two-branch type, and the three-branch type. Among the two-branch types, there are two subtypes, of which, the B4-B5 type has the most common anatomical pattern of the left upper lobe lingula bronchus (7). Based on the positions of B4 and B5, the B4-B5 type can be further classified as follows: vertical (Type I) and horizontal (Type II). In this study, 4,276 (91.13%) patients had Type I, while 416 (8.87%) had Type II. The incidence of Type I was significantly higher than that of Type II (P<0.001).

Based on the positional relationship between B4a and B4b, and that between B5a and B5b, the B4-B5 type bronchus of the lingula can be further classified into the following eight subtypes: Type I-a (4,021 cases, 85.70%); Type I-b (109 cases, 2.32%); Type I-c (90 cases, 1.92%); Type I-d (56 cases, 1.19%); Type II-a (182 cases, 3.88%); Type II-b (71 cases, 1.51%); Type II-c (132 cases, 2.81%); and Type II-d (31 cases, 0.66%). For the arterial pattern of the B4-B5 type lingula, the following results were observed: interlobar type: 3,186 cases (67.90%); mediastinal type only: 865 cases (18.44%); and mediastinal combined with interlobar type: 641 cases (13.66%). The incidence of the mediastinal type was approximately 32.10%. For the venous pattern of the B4-B5 type lingula, the findings were as follows: one-branch type: 2,324 cases (49.53%); two-branch type: 1,862 cases (39.68%), of which 714 (15.22%) showed V4 and V5, 547 (11.66%) showed V4 + V5b and V5a, and 333 (7.10%) showed V4a and V4b + V5; three-branch type: 506 cases (10.78%), of which 126 (2.69%) showed V4, V5a, and V5b, and 380 (8.10%) showed V4a, V4b + V5b, and V5a. The lingula consists of four subsegments (S4a, S4b, S5a, and S5b), and different bronchial patterns in the lingula lead to eight possible arrangements of these subsegments. In this study, we analyzed the characteristics of the Type I and Type II patients, and found no significant differences between the two groups in terms of age, gender, smoking history, BMI, cardiothoracic ratio, chronic disease history, or pulmonary function (FEV1, %FEV1, FEV1/FVC, and %DLCO).

For early stage lung cancer, the best treatment is early surgery. To ensure surgical success and long-term quality of life, accurate preoperative lung anatomy analysis by radiologists and surgeons is essential to choose the optimal surgical approach (11,13). Therefore, it is crucial to accurately identify the branching patterns of segmental bronchi and delineate the corresponding lung segments. In practice, we have observed a high variability in the bronchial structure of lung segments, and only by mastering the various types of segmental bronchial branching can pulmonary lesions be accurately located and precise sub-lobar resections guided (10). Using a novel 3D volumetric analysis system, we showed that the lingula volume is highly correlated with the bronchial branching pattern and the cross-sectional area of the lingula bronchus. The B⁴ diameter was significantly larger in Type I than Type II (4.39±0.81 vs. 3.31±0.37 mm, P<0.001), and there was no significant difference in the diameter between B4+5 and B5. The lingula volume was significantly larger in Type I than Type II (330.48±84.17 vs. 280.76±56.22 mL, P=0.01). Compared to Type II, Type I had a significantly larger lingula volume relative to the total lung volume, left lung volume, and left upper lung volume. The lingula volume was also highly correlated with the arterial branching pattern of the lingula. The mediastinal type lingula artery was associated with larger lingula volumes (P<0.001). Compared with the interlobar type group, the mediastinal type group had a significantly larger lingula segment volume/total lung volume (8.96%±1.33% vs. 7.93%±1.07%, P<0.001), a larger lingula segment volume/left lung volume (19.73%±1.57% vs. 16.96%±2.39%, P<0.001), and a larger lingula segment volume/left upper lung volume (37.33%±2.65% vs. 31.86%±3.87%, P<0.001).

In this study, we analyzed the bronchial and vascular patterns of the lingula and highlighted the differences between our results and a previous report (18). To our knowledge, research on the correlation between bronchial branching patterns and lung segment volume was not common.. In this study, a 3D-CT analysis was used to measure the diameter of the lingula bronchus and the lingula volume. This semi-automated measurement provided highly reproducible anatomical data with excellent inter-observer consistency. Further, it was primarily used to identify segmental bronchi and vessels, such as intersegmental veins, for the preoperative evaluation of lung segmentectomy, which is important, as variations in pulmonary vessels and abnormal branching significantly affect the technical difficulty and surgical risk (10,19,20). There were relatively a few reports on the branching patterns of lingula bronchi and subsegmental bronchi. Different branching patterns may form during embryonic development. Onuki et al. (21) speculated that the axis rotation of the left upper lung during embryogenesis could affect the development direction of the lingula bronchus. In other words, as the bronchus grows in the chest, even a slight rotation of the bronchial axis may affect the development of the lingula bronchus. The use of 3D volumetric measurements has helped surgeons to gain a better and more detailed understanding of lung anatomy, enabling more precise sub-lobar resections and shortening the learning curve (10). In the context of regenerative medicine, the relationship between the bronchial vascular system and lung development has become even more important.

This study had a number of limitations, including a potential selection bias due to its retrospective nature. The limitation of this study was based on data from a single institution, to confirm its broader applicability, external validation of the classification was still necessary, which is expected to be improved in future work. This was the first study to report using a novel 3D reconstruction volumetric measurement method to show that the branching patterns of pulmonary bronchi and pulmonary arteries significantly affect lung volume. This study provided insights into the role of the bronchial and vascular systems in lung development. The results of our study may be particularly useful for the anatomical study of the left lung lingula.

Conclusions

The variation pattern of the lingula is far more complex than expected. Preoperative CT-based 3D reconstruction of pulmonary arteries, veins, and bronchi is of great significance. It can help understand the variations, accurately locate lesions before surgery, and effectively plan operations. The results of this study could help surgeons to better understand the anatomy of the lingula and perform segmentectomies more accurately.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-510/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-510/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-510/prf

Funding: This study was supported by the Medical and Health Research Program (No. A20-2-015), and Science & Technology Bureau of Yichang.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-510/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The protocol of this study was approved by the institutional review board of Yichang Central People’s Hospital (No. 2023-190-01) and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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