Observation of bronchial anatomy and variation of the middle lobe of the right lung based on three-dimensional reconstruction of lung CT

Abstract

Purpose

To explore the anatomical types and variations of lung segments and subsegment bronchi based on CT 3D reconstruction technology, and to provide anatomical theoretical support for thoracic surgeons in terms of surgical techniques.

Methods

The 3D CT reconstructed images of 541 patients were retrospectively analyzed. We explored the anatomical structure of the bronchi in the middle lobe of the right lung, sorted out the variations, and classified them in detail according to different bronchial types.

Results

In the CT 3D reconstruction of 541 patients, the bronchial anatomical types of the right middle lobe were divided into two types. There were 530 cases (98.0%) of two-branched type and 11 cases (2.0%) of three-branched type, and no four-branched type was found in the data of this paper. In addition, the spatial relationship between B₄ and B₅, and the spatial relationship between subsegmental bronchi B_4a, B_4b, B_5a, and B_5b are analyzed. The most common anatomical type and spatial relationship of the right middle lobe bronchi in the two-branched type were B₄ and B₅ in the external-internal relationship, B_4a and B_4b in the external-internal relationship, and B_5a and B_5b in the upper and lower relationship, and this subtype was 416 cases (76.9%). In addition, 23 cases (3.9%) were found to have a spatial relationship between B₄ and B₅ in the right middle lobe similar to the lingual bronchial subtype in the left upper lobe.

Conclusion

We used a large number of CT 3D reconstructed images to explore the anatomical types and variations of the bronchi in the middle lobe of the right lung. Thoracic surgeons can use our data to guide increasingly delicate lobectomy and segmentectomy.

Introduction

Lung cancer has become the most common malignant tumor in the world [1]. With the early diagnosis and early screening of lung malignant tumors and the increasing sophistication of thoracic surgery, lung segmentectomy has become the most important emerging surgical method due to its small damage and the prognosis of lobectomy, and the number of patients who need to undergo lung segmentectomy is increasing [2,3,4]. Segmentectomy requires accurate intraoperative identification and identification of the bronchi at the level of lung segments and subsegments, which undoubtedly poses new challenges to thoracic surgeons [5]. In today’s challenging world, CT 3D reconstruction technology is developing rapidly, which can provide thoracic surgeons with a new way to intuitively identify the passage of bronchi, arteries and veins at all levels, and can provide strong technical support for more delicate surgical methods [6,7,8]. Exploring the anatomical types and variations of the pulmonary segment bronchi and subsegment bronchi can provide an important imaging reference for thoracic surgeons. However, there are not a large number of relevant articles to clearly explain such a detailed anatomical structure and variation of the bronchi in the middle lobe of the right lung, and the purpose of this article is to clearly point out the route and variation types of the bronchi in the middle lobe of the right lung, so as to provide important guidance for pulmonary segment surgery in thoracic surgery.

Patients and methods

Patient preparation and examination

This is a retrospective study that included the imaging data of 541 patients who underwent thin-slice CT examination in the Department of Thoracic Surgery of Hebei General Hospital from October 2020 to October 2022.Among them, there were 249 males and 292 females, with an average age of 56 years. All procedures for the human participants involved in this study are consistent with the Declaration of Helsinki (revised 2013). The Research Ethics Committee of Hebei General Hospital approved this retrospective study (No. 2024-LW-070). Because this study is retrospective, it is without the consent of the patient. Bronchial changes in the middle lobe of the right lung were classified and summarized.

Reconstruction of 3D-CTAB imaging

The bronchial CT images of the patient were scanned by a 128-slice CT machine from Siemens Definition Flash (Siemens AG, Germany). Scanning parameters: tube voltage 120 kV, tube current 200 ~ 300 mA, scanning layer thickness 2 mm, layer spacing 1 mm. The obtained data was transferred to 3D reconstruction software (Infer Operate Thorax Planning), which was used to convert the data into a 3D structural bronchial model. The 3D reconstruction was completed and verified by at least two thoracic surgeons, and the accuracy of the reconstruction was confirmed by mutual validation with the 2D CT images.

Definition of arterial vessels in the middle lobe of the right lung (RML)

We use the same nomenclature to describe the segmental structure based on the study by Boyden et al. [9, 10]B_X is the location of the normal lung segment or subsegment from the adjacent lung segment or subsegment bronchi, the specific lung segment bronchi is indicated by Arabic numerals on the corresponding letters, and the subsegment bronchi is named with lowercase English letters. The middle lobe of the right lung is mainly segmented by the bronchial shape of the middle lobe of the right lung, and its shape variation is relatively small, and the bronchi of each segment joins the middle lobe bronchus and finally joins the right main bronchus.

Statistics

All statistical analyses were performed using SPSS 26.0 (SPSS, Chicago, IL, USA). Non-normally distributed continuous variables are described in terms of mean, and count data are described in terms of frequency and percentage.

Results

Among the 541 patients in this study, there were two types of bronchi in the right middle lobe (Table 1):1. There were 530 cases (98.0%) of bibranched type, of which 508 cases (93.9%) were normal B₄ and B₅ types, and the rest were B_4b + B₅ co-trunk cases (3.3%) (Fig. 1),3 cases (0.6%) of B_5a + B₄ co-trunk (Fig. 2) and B_5b + B₄ co-trunk in 1 case (0.2%) (Fig. 3).No B_4a + B₅ co-trunk was found in this study.2. There were 11 cases (2.0%) of the three-branched type, which were B_4a, B_4b, B_5a + B_5b 5 (0.9%) (Fig. 4), B_4a, B_5a, B_4b + B_5b 5 (0.9%) (Fig. 5) and B_5a, B_5b, B_4a + B_4b 1 (0.2%) (Fig. 6), but there were no three-branched types of B_4b, B_5b, B_4a + B_5a.No four-branched type is found in the data in this article. The results of these studies are similar to those of previous studies, suggesting that the middle lobe bronchus of the right lung are more common in a bibranched type.

Table 1 Anatomical types and proportions of bronchus in the right middle lobe of the 541 patients

Fig. 1

3D model of the B_4b+B₅ cotrunk of the middle lobe of the right lung

Fig. 2

3D model of the B_5a+B₄ cotrunk of the middle lobe of the right lung

Fig. 3

3D model of the B_5b+B₄ cotrunk of the middle lobe of the right lung

Fig. 4

3D model of the B_4a, B_4b, B_5a+B_5b in the bronchial trifurcation of the middle lobe of the right lung

Fig. 5

3D model of the B_4a, B_5a, B_4b+B_5b in the bronchial trifurcation of the middle lobe of the right lung

Fig. 6

3D model of the B_5a, B_5b, B_4a+B_4b in the bronchial trifurcation of the middle lobe of the right lung

In addition, the spatial relationship between B₄ and B₅, and the spatial relationship between subsegmental bronchi B_4a and B_4b and B_5a and B_5b were also analyzed, among which the most common anatomical type and spatial relationship of the right middle lobe bronchi in the two branched types were B₄ and B₅ in the external and internal relationship, B_4a and B_4b in the external and internal relationship, and B_5a and B_5b in the upper and lower relationship, and this subtype was 416 cases (76.9%) (Fig. 7).In addition, there were the following subtypes of B₄ and B₅ external and internal relationship: 1. B_4a and B_4b showed an up-down relationship, and B_5a and B_5b showed an up-down relationship in 8 cases (1.5%) (Fig. 8); B_4a and B_4b were externally and internally related, and B_5a and B_5b were externally and internally related in 8 cases (Fig. 9);3. B_4a and B_4b showed an up-down relationship, and B_5a and B_5b showed an external-internal relationship in one case (0.2%) (Fig. 10).When B₄ and B₅ were in an upward and downward relationship, there were the following classifications: 1. B_4a and B_4b showed an external and internal relationship, and B_5a and B_5b showed an upward and downward relationship in 32 cases (5.9%) (Fig. 11); There were 19 cases (3.5%) of B_4a and B_4b, and B_5a and B_5b (Fig. 12);3. B_4a and B_4b were in an up-and-down relationship, and B_5a and B_5b were in an up-down relationship in one case (0.2%) (Fig. 13).In this paper, there is no case where B_4a and B₅ are in an upward and downward relationship, B_4a and B_4b are in an upward and downward relationship, and B_5a and B_5b are in an external and internal relationship. In addition, 23 cases (4.3%) were found to have a spatial relationship with B₄ and B₅ in the middle lobe of the right lung, similar to the B₄ and B₅ lingual subtypes of the upper lobe of the left lung. (Fig. 14)

Fig. 7

A 3D model of the middle lobe bronchi of the right lung in which B₄ and B₅ are in an external-internal relationship, B4a and B4b are externally and internally, and B_5a and B_5b are in an up-down relationship

Fig. 8

A 3D model of the bronchi B₄ and B₅ in the middle lobe of the right lung, B_4a and B_4b in an up-down relationship, and B_5a and B_5b in an up-down relationship

Fig. 9

A 3D model of the middle lobe bronchi of the right lung in which B₄ and B₅ are externally and internally, B_4a and B_4b are externally and internally, and B_5a and B_5b are externally and internally

Fig. 10

A 3D model of the bronchi B₄ and B₅ in the middle lobe of the right lung, B_4a and B_4b in an up-down relationship, and B_5a and B_5b in an external-internal relationship

Fig. 11

A 3D model of the middle lobe bronchus of the right lung in which B₄ and B₅ are in an up-down relationship, B_4a and B_4b are in an external-internal relationship, and B_5a and B_5b are in an up-down relationship

Fig. 12

A 3D model of the middle lobe bronchi of the right lung in which B₄ and B₅ are in an upper-inferior relationship, B_4a and B_4b are in an external-internal relationship, and B_5a and B_5b are in an external-internal relationship

Fig. 13

A 3D model of the middle lobe bronchi of the right lung in which B₄ is in an up-down relationship with B₅, B_4a is in an up-down relationship with B_4b, and B_5a is in an up-down relationship with B_5b

Fig. 14

A 3D model of the bronchial B₄ and B₅ of the middle lobe of the right lung resembling the bronchial structure of the lingual segment

Discussion

Lobectomy and segmental resection is the standard surgical method for the treatment of lung diseases, and it is essential to have a good grasp of the anatomy and special variations of the bronchi in the lungs to improve the safety and quality of the surgery [11, 12]. The anatomical types of bronchial branches of lung segments and subsegments are complex and diverse, and for patients with early-stage lung cancer who currently need to undergo lobectomy or even segmentectomy, the possible anatomical variations will become an obstacle to the identification of anatomical structures during surgery, and may even cause misjudgment. Traditional autopsy and tomotomy can only observe bronchial anatomy from a cross-sectional, coronal or sagittal plane, but CT 3D reconstruction technology can more intuitively display the branch types and anatomical variations of the bronchi in the lung segment, which provides a great guarantee for preoperative planning and intraoperative safety [13,14,15] (Table 2).

Table 2 The Spatial relationship and proportion of bronchial in the right middle lobe of the 541 patients

In recent years, thoracoscopic sublobectomy has been shown to be safe and effective, and Hirohisa Kato et al. studied 357 consecutive patients who underwent thoracoscopic anatomical sublobectomy for lung cancer between March 2005 and May 2020, suggesting that thoracoscopic subsegmental resection can be used for ground-glass opacity-dominated lung cancer < 1.5 cm, if adequate margins can be ensured.

Based on CT data, the bronchi of the middle lobe of the right lung was reconstructed and analyzed, and the dissection of the bronchi of the middle lobe of the right lung was systematically studied. In this study, the classification methods of multiple studies were combined to classify and statistically analyze the anatomy of the middle lobe of the right lung in the most convenient way for surgeons to operate [16]. A meta-analysis of patients with operable stage IA non-small cell lung cancer was performed by Liwei Song et al. on subsegmentectomy versus segmentectomy, with a total of 325 patients undergoing subsegmentectomy and 904 patients undergoing segmentectomy participating in the analysis. Suggests that perioperative outcomes for subsegmentectomy and segmentectomy are comparable. Subsegmental resection may be an alternative treatment for deep tumors that are less than 1.5 cm in size and consist primarily of ground-glass opacities (GGOs) [17]. Xiayi Lv et al. studied the survival rates of 861 patients with early right middle lobe non-small cell lung cancer after lobectomy and sublobectomy, and the prognosis of lobectomy and sublobectomy was comparable for patients with stage IA right middle lobe ≤ 1 cm NSCLC [18]. Zhang Min et al. performed thoracoscopic right middle lobe subsegmentectomy in 94 patients, and confirmed that thoracoscopic right middle lobe subsegmentectomy was feasible and safe. Preservation of lung parenchyma may be valuable in patients with non-invasive lung cancer, multiple lung cancer, and benign disease [19]. Based on the above research, this study was the first to reconstruct and analyze the bronchi of the middle lobe of the right lung based on CT data, and systematically studied the anatomy of the bronchi of the middle lobe of the right lung. In this study, the classification methods of multiple studies were combined to classify and statistically analyze the anatomy of the middle lobe of the right lung in the most convenient way for the surgeon to operate and preserve as much lung function as possible.

Nagashima et al., analyzing CT 3D reconstructed images from 270 patients, found that all the middle lobe bronchus of the right lung were single-branched, i.e., B₄ + B₅.[20]The results of this study are consistent with this, and the anatomical types of the middle bronchi of the right lung are further divided into two-branched and three-branched types according to the number of branches, and the anatomical types of the middle bronchi of the right lung are further supplemented. Among the two-branched types, there is also co-trunk, the most common is B4b + B5 co-trunk. The number of B_4a, B_5a, B_4b + B_5b and B_4a, B_4b, B_5a + B_5b was the same in the three-branch type. In addition, the spatial relationships between the bronchial tubes are also supplemented, the most common of which are B₄ and B₅ in the external-internal relationship, B_4a and B_4b in the external-internal relationship, and B_5a and B_5b in the upper and lower relationship.

Ghaye et al. found that 23% of the B₄, B₅ bronchi in the middle lobe of the right lung have an up-and-down position relationship similar to that of the B₄, B₅ bronchi in the tongue segment of the left upper lobe; [21]However, in this study, only 23 patients (4.3%) were found to have an up-and-down position relationship similar to that of B₄ and B₅ bronchi in the tongue segment of the left upper lobe, which was much lower than reported by Ghaye et al. We analyzed this may be related to the small sample size (30 cases) of Ghaye et al. Due to the small size of the right middle lobe and the smaller residual lung tissue after lung segment surgery, complications such as torsion and atelectasis are prone to occur after surgery, so the preoperative thin-slice CT examination of the chest and the three-dimensional reconstruction of CT are performed to correctly evaluate the anatomical type of the lingual bronchi of the middle lobe of the right lung and clarify the spatial position relationship of the bronchi of the lung segment, which plays an important role in guiding the successful implementation of the operation.

Conclusion

In summary, the middle lobe and subsegment bronchi of the right lung have extremely complex anatomical typologies and rare variations, and we used a large number of CT 3D reconstructed images to explore and name the bronchial pattern of the middle lobe of the right lung. Thoracic surgeons should be familiar with the various anatomical types and subsegmental anatomical types and relatively common variants in order to guide delicate lobectomy and segmental resection. There are some limitations in this study, this study is a retrospective study, and the sample size is relatively small.