Postoperative lung geometric repositioning after right upper lobectomy: the role of thoracic morphology configuration

Introduction

Lobectomy remains the standard curative operation for resectable lung cancer (1). Postoperative pulmonary function and compensatory adaptation, however, vary widely among individuals and differ by the resected lobe. Longitudinal studies have highlighted marked lobe-specific variability, suggesting that this heterogeneity reflects an interplay between thoracic morphology and functional determinants (2,3). Clarifying how postoperative lung geometry relates to functional outcomes therefore remains an unmet need.

Malignant tumors arise most frequently in the right upper lobe (4). Right upper lobe removal creates a large cranial-anterior space that is filled by upward relocation of the residual middle and lower lobes. This relocation can distort the bronchus intermedius and the middle lobe bronchus, causing bronchial kinking associated with symptoms and reduced functional lung volume (5).

Prior work after right upper lobectomy (RUL) has mainly addressed discrete events such as middle lobe atelectasis (MLA), bronchial kinking, and true lobar rotation (6-11). In contrast, the broader process of three-dimensional (3D) repositioning within the thoracic morphology and its relationship to postoperative functional recovery has not been quantitatively characterized.

We developed a computed tomography (CT)-based framework to quantify 3D repositioning after RUL, capturing sagittal bronchial axis deviation (B4/5 and B6) and plane-based rotation-like deformation of the middle lobe (Figures 1-3). We examined whether thoracic morphology biases the repositioning pattern and whether these geometric markers are associated with postoperative residual-lobe expansion, potentially informing lobe-specific heterogeneity in postoperative pulmonary function. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2026-1-0218/rc).

Figure 1 Sagittal assessment of bronchial axis deviation and definition of deviation-dominant patterns (Type B6 vs. Type B4/5). All panels are based on sagittal CT assessment. (A) Pre- and postoperative angles of the middle lobe bronchus (B4/5) and the superior segmental bronchus (B6) were measured relative to the right main bronchus/bronchus intermedius axis. (B,C) Based on sagittal angle changes (pre − post), cases were classified into two deviation-dominant patterns: Type B6, in which ΔB6 exceeds ΔB4/5, and Type B4/5, in which ΔB4/5 exceeds ΔB6. (D) Scatter plot of sagittal angle changes (y-axis: ΔB6; x-axis: ΔB4/5) with the identity line (y = x) as the decision line; points above the identity line were classified as Type B6 and those below as Type B4/5 (Type B6, red circles; Type B4/5, blue circles). The cases shown in panels (B) and (C) are indicated by arrows in panel (D). CT, computed tomography; MLA, middle lobe atelectasis.

Figure 2 Post RUL repositioning patterns and corresponding thoracic morphology. (A) Schematic of the Type B6 repositioning pattern after RUL, in which the superior segment (S6) ascends to form the new apex and the middle lobe relocates anteromedially. (B) Schematic of the Type B4/5 repositioning pattern, in which the middle lobe migrates cranially to form the apex while the lower lobe preferentially fills the posterobasal recess. (C,D) Representative thoracic morphologies corresponding to each pattern: a barrel-shaped thorax for Type B6 (C) and a flatter thorax for Type B4/5 (D) (thoracic morphology assessed using the H/AP ratio and the 8th-rib angle, as defined in Methods). H/AP, thoracic height-to-anteroposterior diameter ratio; RUL, right upper lobectomy.

Figure 3 Plane-based rotation metrics and discriminant boundary. (A) Coronal (frontal) rotation component: the angle between the tracheal axis and the S4/S5 intersegmental-plane axis, with clockwise rotation defined as positive; ΔY = Ypost − Ypre (degrees). (B) Right-lateral sagittal rotation component: the angle between the tracheal axis and the middle-lower interlobar-plane axis, with counterclockwise rotation defined as positive; by convention, ΔX = Xpre − Xpost (degrees). (C) Scatter plot of ΔX (x-axis) and ΔY (y-axis) by deviation-dominant pattern (Type B6, red circles; Type B4/5, blue circles). The solid line indicates the discriminant boundary (Z=0) defined as Z = ΔY − 27.038ΔX − 90.265; cases were classified as Type B6 for Z>0 and Type B4/5 for Z≤0. Apparent classification performance was 90.9% for Type B6 (Wilson 95% CI: 62.3–98.4%) and 80.0% for Type B4/5 (Wilson 95% CI: 49.0–94.3%). The cases shown in panels (A) and (B) are indicated by arrows in panel (C). CI, confidence interval.

Methods

We performed 91 RULs at Kagoshima University Hospital between October 2016 and July 2018. Exclusion criteria were prior thoracic surgery (n=17), additional lobar resections and/or combined resections for mediastinal or chest-wall tumors (n=19), persistent intraoperative adhesions in chest closure (n=8), and insufficient imaging or clinical data (n=21). The final cohort comprised 26 patients, including 5 who developed postoperative MLA. The postoperative CT used for analysis was the index postoperative deep-inspiration CT obtained at 6 months after surgery [interquartile range (IQR), 4–8], in accordance with our institutional follow-up protocol. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The Kagoshima University Hospital Ethics Committee approved this retrospective study (No. 210265). Given the retrospective design, written informed consent was waived, and an opt-out procedure was provided. The clinical care and imaging data were obtained from Kagoshima University Hospital, and the Ethics Committee of Kagoshima University Hospital served as the responsible review board for this study.

Thoracic morphology

Thoracic morphology was assessed on preoperative deep-inspiration CT. On the sagittal plane, we measured thoracic height [apex of the right lung to the highest point (H) of the right diaphragmatic dome, cm] and the anteroposterior (AP) diameter (maximal distance from the right anterior to posterior chest wall, cm) (Figure 2C,2D). On the axial plane, we measured the right hemithoracic width (from the vertebral body center to the right lateral chest wall, maximum cm). To capture rib trajectory with minimal influence from costal cartilage, we defined the 8th-rib angle on the sagittal plane as the angle between the long axis of the right 8th rib and the horizontal plane (Figure 2C,2D).

Bronchial axis deviation

Residual bronchial axis deviation was evaluated using paired pre- and postoperative CT datasets analyzed in a 3D workstation (SYNAPSE VINCENT ver. 7.0; Fujifilm). We extracted centerlines for the trachea, right main bronchus, bronchus intermedius, the middle lobe bronchus (B4/5), and the superior segmental bronchus (B6). On the coronal plane, we measured displacement of the right main/bronchus intermedius axis relative to the tracheal axis (Figure S1). On the sagittal plane, we measured angular deviation of B4/5 and B6 relative to the right main/bronchus intermedius axis (Figure 1A). Because bronchial axis deviation is inherently 3D, we quantified angles on standardized coronal and sagittal planes using orthogonal projection of each 3D centerline onto the respective plane, and measured the projected orientations consistently across pre- and postoperative scans.

Rotation of the middle lobe

True axial spin of the bronchial lumen cannot be directly measured on CT. Therefore, middle lobe rotation was inferred from rotation of parenchymal reference planes that represent the lobe as a whole. Specifically, we used two orthogonal components:

• Coronal component (ΔY): on the coronal (frontal) plane, we focused on the intersegmental plane between S4 and S5 and measured the angle between this plane’s axis and the tracheal axis; clockwise rotation was defined as positive, and the coronal rotation was expressed as ΔY= Ypost – Ypre (degrees) (Figure 3A).
• Sagittal component (ΔX): on the sagittal (right-lateral) plane, we focused on the interlobar plane between the middle and lower lobes and measured its angle relative to the tracheal axis; counterclockwise rotation was defined as positive, and—per our convention in Figure 3B—the sagittal rotation was expressed as ΔX = Xpre – Xpost (degrees).

Together, ΔY and ΔX capture orientation changes of two anatomically meaningful, approximately orthogonal parenchymal planes, serving as a pragmatic surrogate of 3D middle-lobe reorientation/twisting rather than true axial bronchial spin.

We also quantified pre- and postoperative volumes of the right upper, middle, and lower lobes (including S6), the bronchus-intermedius cross-sectional area (CSA) (plane orthogonal to its centerline just distal to the upper-lobe takeoff), the length of the right main/bronchus-intermedius segment, the middle lobe bronchus cross-sectional area (the B4/B5 origin orifice), and the B4/5 intrabronchial length (orifice to the B4/B5 bifurcation).

Additional variables included age, body mass index, smoking history, surgical approach (open vs. thoracoscopic), extent of mediastinal lymph-node dissection (≤ND2a-1 vs. ND2a-2), and preoperative pulmonary function (FVC, FEV₁, FEV₁/FVC, %DLCO). The degree of incomplete interlobar separation between the middle and lower lobes was graded on CT using a pragmatic 4-point scale (0 = complete separation; 3 = complete non-separation), and patients were compared as Grade 0–1 versus Grade 2–3 (Tables 1,2, Tables S1,S2).

Reproducibility of imaging measurements

To assess measurement reproducibility, two observers independently repeated the key geometric measurements on the same image datasets, including thoracic morphology indices (H/AP ratio and 8th-rib angle), sagittal bronchial axis-deviation metrics (ΔB4/5 and ΔB6), and plane-based rotation components (ΔX and ΔY). For intraobserver reproducibility, the primary observer repeated the measurements after a washout interval with the cases re-ordered and blinded to the initial results. Reliability was quantified using the intraclass correlation coefficient (ICC) with 95% confidence intervals (CIs), applying a two-way random-effects model with absolute agreement for single measurements {ICC[2,1]}.

Statistical analyses

Continuous variables were summarized as median (IQR), and categorical variables as n (%). Between-group comparisons—normal vs. MLA and repositioning patterns Type B6 vs. Type B4/5—used the Mann-Whitney U test for continuous variables and Fisher’s exact test for categorical variables. For the schematic classification shown in Figure 1D, repositioning patterns (Type B6 vs. Type B4/5) were additionally categorized using a simple boundary on the sagittal-plane angle changes, where the identity line (ΔB6 = ΔB4/5) served as the decision line (i.e., ΔB6-dominant vs. ΔB4/5-dominant change). Discriminant analyses (exploratory) classified subtypes using a rotation-based score derived from ΔX and ΔY; performance was summarized as apparent per-class accuracy with Wilson 95% CIs. Associations in 2×2 contingency tables were tested with two-sided Fisher’s exact test. In addition, linear-regression analyses were performed to relate geometric changes to postoperative lobe expansion. The primary outcomes were the middle lobe and lower-lobe volume ratios (post/pre). Univariable models regressed each outcome on individual angular predictors—thoracic morphology, ΔB4/5, ΔB6 and ΔX on the sagittal planes, ΔY on the coronal planes—and on the 3D residual-lung repositioning patterns (Type B6 vs. Type B4/5), with 95% CIs and two-sided P values. All analyses were performed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan) and SPSS (Dr SPSS II for Windows, Standard Version 26.0; SPSS Inc., Chicago, IL, USA). Statistical significance was set at P<0.05.

Given the small sample size, the discriminant analysis was intended for exploratory phenotyping and visualization; we therefore report apparent (in-sample) accuracy and do not claim generalizable predictive performance.

Results

After RUL, 3D lobe repositioning of the residual middle and lower lobes within the right hemithorax was accompanied by bronchial axis deviation and apparent rotational changes. For axis deviation, the first-step displacement of the right main bronchus/bronchus intermedius axis relative to the tracheal axis was measured on the coronal plane; in all patients, this axis shifted cranially after RUL (Figure S1A). Superimposed on this cranial displacement, a second-step pattern emerged on sagittal measurements relative to the bronchus intermedius axis: one pattern showed predominant cranial deviation of B6 (Figure 1B), whereas the other showed predominant cranial deviation of B4/5 (Figure 1C). According to the dominant deviating branch, these were defined as the B6-dominant cranial deviation type (Type B6) and the middle lobe bronchus-dominant cranial deviation type (Type B4/5) (Figure 1D).

Consistent with bronchial deviation dominance, the 3D residual-lung repositioning patterns were categorized into two subtypes: a pattern in which S6 reached the newly formed lung apex (Type B6, n=13; Figure 2A) and a pattern in which the middle lobe alone reached the apex (Type B4/5, n=13; Figure 2B). Preoperative thoracic morphology significantly differed between these subtypes, with Type B6 associated with a barrel-shaped thorax and Type B4/5 with a flatter thorax. Specifically, thoracic height (H; P=0.01), H/body height (P<0.001), anteroposterior diameter (AP; P=0.02), AP/body height (P=0.03), H/AP (P=0.001) and the 8th-rib angle (P<0.001) differed between groups (Table 1). In contrast, no differences were observed in surgical approach, preoperative lobar volumes, bronchial lengths (B4/5 and B6), or cross-sectional areas of B4/5, B6, and the bronchus intermedius (Table S1). Regarding postoperative volume behavior, Type B6 showed a larger S6 volume change ratio (post/pre) (P=0.03), whereas the middle lobe volume change ratio (post/pre) (P=0.22) and the combined middle + lower lobe volume change ratio (post/pre) (P=0.36) did not differ between subtypes (Table 1).

Rotational behavior of the middle lobe was evaluated by quantifying rotations of representative parenchymal planes on coronal and sagittal projections (Figure 3). On the projected coronal (frontal) plane, the angle between the tracheal axis and the S4–S5 intersegmental plane axis was measured with clockwise rotation defined as positive (Figure 3A; ΔY = Ypost − Ypre). On the projected right-lateral sagittal plane, the angle between the tracheal axis and the middle-lower interlobar plane axis was measured with counterclockwise rotation defined as positive (Figure 3B; ΔX = Xpre − Xpost). Discriminant boundary was defined as Z = ΔY − 27.038ΔX − 90.265 (boundary at Z=0); cases were classified as Type B6 for Z>0 and Type B4/5 for Z≤0. Apparent classification performance was 90.9% for Type B6 (Wilson 95% CI: 62.3–98.4%) and 80.0% for Type B4/5 (Wilson 95% CI: 49.0–94.3%). This boundary was used for exploratory visualization of subtype separation. In addition, in the S6-apical pattern, 10 of 11 cases (90.9%) met the combined directional signature of Ypost − Ypre >0° and Xpre − Xpost <0° (Figure 3C).

Interobserver reproducibility was good to excellent across key measurements {ICC[2,1], absolute agreement}: H/AP ratio (ICC =0.93, 95% CI: 0.84–0.97), 8th-rib angle (ICC =0.90, 95% CI: 0.78–0.96), ΔB4/5 (ICC =0.88, 95% CI: 0.72–0.95), ΔB6 (ICC =0.91, 95% CI: 0.80–0.96), ΔX (ICC =0.85, 95% CI: 0.65–0.93), and ΔY (ICC =0.87, 95% CI: 0.70–0.94). Intraobserver reproducibility was similarly good to excellent {ICC[2,1]}: H/AP ratio (ICC =0.88, 95% CI: 0.72–0.94), 8th-rib angle (ICC =0.91, 95% CI: 0.80–0.96), ΔB4/5 (ICC =0.87, 95% CI: 0.70–0.94), ΔB6 (ICC =0.89, 95% CI: 0.76–0.95), ΔX (ICC =0.87, 95% CI: 0.70–0.94), and ΔY (ICC =0.86, 95% CI: 0.68–0.92).

No variable showed an association with the combined middle + lower lobe volume change ratio (post/pre): 3D residual-lung repositioning patterns (Type B6 vs. Type B4/5; P=0.42), thoracic morphology (H/AP ratio, P=0.28; 8th-rib angle, P=0.61), bronchial axis deviation (ΔB4/5, P=0.06; ΔB6, P=0.65), or rotational metrics (ΔY, P=0.68; ΔX, P=0.69) (Table 3).

Five patients had MLA on the index postoperative CT. In these cases, classifying the 3D residual-lung repositioning patterns (Type B6 vs. Type B4/5) based on residual-lung configuration alone was difficult (Figure 4). However, focusing on bronchial axis deviation allowed assignment to Type B6 or Type B4/5, suggesting correspondence to the respective repositioning patterns (Figure 4). MLA occurred in both subtypes (Type B6, n=2; Type B4/5, n=3). Across the entire cohort (n=26), comparison of baseline factors between the normal expansion group (n=21) and the MLA group (n=5)—including thoracic morphology, lobar volumes, pulmonary function, bronchial measurements, surgical factors, and the degree of incomplete interlobar separation—showed that the MLA group had a lower combined middle + lower lobe volume change ratio (post/pre) (P=0.02), whereas no preoperative factor significantly differed between groups (Table 2 and Table S2).

Figure 4 MLA cases and classification by bronchial axis deviation dominance. (A,B) Representative postoperative CT cases with MLA. Because postoperative lobe configuration alone may not clearly indicate the repositioning pattern, MLA cases were classified using the deviation-dominant rule based on sagittal bronchial axis deviation (Figure 1D), i.e., whether ΔB6 exceeded ΔB4/5 (Type B6) or ΔB4/5 exceeded ΔB6 (Type B4/5). CT, computed tomography; MLA, middle lobe atelectasis.

Discussion

This study provides a quantitative, CT-based description of thorax-driven 3D repositioning after RUL and links this process to clinically recognizable geometric responses—sagittal bronchial axis deviation (B6- vs. B4/5-dominant change) and a plane-based, rotation-like deformation of the middle lobe. The focus on RUL is clinically meaningful because RUL resection creates a large cranial-anterior space that must be filled by upward relocation of the residual lobes, a configuration that has been implicated in bronchial kinking and MLA and may contribute to the marked lobe-specific variability in postoperative recovery reported in longitudinal functional studies (2,3,5).

After RUL, thoracic morphology appeared to constrain the 3D repositioning of the residual middle and lower lobes, which was accompanied by a characteristic dominance pattern of bronchial axis deviation (Table 1, Figure 1D). Specifically, the 3D residual-lung repositioning patterns segregated into Type B6 and Type B4/5: Type B6 was associated with predominant cranial axis deviation of B6, whereas Type B4/5 was associated with predominant cranial axis deviation of B4/5 (Figure 1B-1D). In addition, the rotational response of the middle lobe differed between patterns; Type B6 tended to show a rotational signature consistent with clockwise deformation on both the coronal (frontal) and right-lateral sagittal projections (Figure 3C). Notably, when considering why geometric markers did not predict postoperative expansion and what this implies about functional determinants, none of the measured geometric indices—including thoracic morphology, repositioning pattern, bronchial axis deviation, or middle lobe rotation-like deformation—were significantly associated with postoperative residual-lobe expansion as assessed by the middle + lower lobe volume ratio (post/pre), even in univariable analyses. This negative geometry–expansion finding is itself informative: in a small cohort it may partly reflect limited power, but it also suggests that postoperative expansion and recovery are influenced by functional determinants beyond geometry [e.g., regional mechanics, diaphragmatic contribution, ventilation–perfusion distribution (2,3,5)], supporting the need for multimodal geometry–function assessment in future studies. In other words, thoracic morphology may shape how the residual lobes are arranged, but because postoperative pulmonary function was not directly analyzed and volume ratio is only an imaging surrogate, functional recovery likely depends on additional non-geometric determinants—supporting future integrated geometry-function assessment (2,3).

Morphology-informed geometric phenotypes after RUL (Type B6 vs. Type B4/5), together with bronchial axis deviation and rotation-like deformation, may help surgeons anticipate postoperative airway configuration and support pattern-aware surveillance for MLA. The lack of a geometry–volume association further suggests that postoperative expansion and recovery depend on functional determinants beyond geometry, motivating integrated geometry–function evaluation in future studies.

Mechanistically, bronchial axis deviation can be viewed as a coupled displacement: a cranial shift of the bronchus intermedius relative to the tracheal axis, with superimposed sagittal dominance of either ΔB6 or ΔB4/5, corresponding to the two 3D repositioning patterns (Figures 1,2; Figure S1A).

In addition to bronchial axis deviation, a rotational response of the middle lobe was observed, which cannot be captured by bronchial centerline angles alone (8). Because true axial bronchial spin is not directly measurable on routine CT, we used a plane-based surrogate—orientation changes of the S4/S5 intersegmental plane and the middle–lower interlobar plane—which complements prior CT-based approaches relying mainly on centerline angles by capturing rotation-like deformation not represented by centerline angles alone: the S4/S5 intersegmental plane on the coronal projection (Figure 3A) and the middle-lower interlobar plane on the right-lateral sagittal projection (Figure 3B). Using these orthogonal components, a discriminant boundary defined as Z = ΔY − 27.038ΔX − 90.265 (boundary at Z=0) classified the 3D residual-lung repositioning patterns with good apparent accuracy (Type B6: 90.9%; Type B4/5: 80.0%). Notably, most Type B6 cases exhibited a consistent directional signature (10/11, 90.9%) (Figure 3C), whereas Type B4/5 more frequently showed the opposite sagittal-direction component (8/10, 80.0%). These findings suggest that thoracic morphology is linked not only to bronchial axis deviation dominance but also to distinct patterns of middle lobe rotation.

Overall, a barrel-shaped thorax tended to align with the Type B6 (B6-dominant) pattern, whereas a flatter thorax tended to align with the Type B4/5 (B4/5-dominant) pattern, with corresponding differences in rotation-like deformation.

From a clinical standpoint, viewing MLA as an ancillary phenotype within the repositioning spectrum helps contextualize our findings. MLA was associated with a reduced middle + lower lobe volume ratio (post/pre) in our cohort. Prior reports have discussed contributors such as bronchial length, lobar volume, bronchial kinking, and middle lobe rotation (6,9-12), but these factors have rarely been examined within an integrated geometric framework. In our data, MLA occurred in both Type B6 and Type B4/5 patterns (Figure 4), suggesting that it is not explained by a single configuration. We propose that MLA may arise when the anatomically narrow middle lobe bronchus becomes functionally compromised under pattern-specific geometric loads—rotation-like deformation in Type B6 versus predominant cranial deviation of B4/5 in Type B4/5—potentially explaining the lack of distinctive preoperative predictors (Table 2, Table S2). Preventive strategies may therefore need to be pattern-specific; middle lobe fixation has been proposed (13-16) and may mitigate rotational deformation in Type B6, whereas its effect on dominant cranial axis deviation, particularly in Type B4/5, requires further study.

This study has several limitations. First, it was a single-center retrospective analysis with a small sample size (n=26), including only five cases of postoperative MLA; therefore, subgroup findings should be interpreted cautiously as exploratory and hypothesis-generating. Accordingly, the classification/discriminant results may be prone to overfitting and should be interpreted as exploratory until validated in independent cohorts. Second, our geometric measurements represent inherently 3D phenomena using planar angles derived from coronal and sagittal projections. Although we standardized measurements by orthogonal projection of 3D centerlines and reference planes, subtle out-of-plane deformation and complex non-coplanar relationships may have been under- or overestimated. Third, the middle lobe rotation metric was an indirect surrogate based on parenchymal reference planes rather than direct measurement of true axial spin of the bronchial lumen, which cannot be captured on CT. Fourth, our analysis reflects geometry at the index postoperative CT; in MLA cases, measurements may partly represent secondary changes at that time, and intermittent/late atelectasis outside the index CT was not assessed. Finally, future studies integrating functional endpoints (spirometry, symptoms, or regional ventilation/perfusion) with geometric descriptors may clarify which functional determinants, beyond geometry, drive postoperative expansion and lobe-specific recovery.

Conclusions

Thoracic morphology was associated with distinct, reproducible 3D repositioning patterns after RUL, characterized by bronchial axis deviation and rotation-like middle-lobe deformation. These geometric signatures provide a framework for postoperative lung rearrangement, while functional postoperative expansion and recovery likely depend on functional determinants beyond geometry alone. MLA occurred in both patterns, supporting potentially pattern-specific mechanisms that warrant validation in larger, function-integrated cohorts.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2026-1-0218/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2026-1-0218/dss

Funding: This research was partially supported by the Research Support Project for Life Science and Drug Discovery [Basis for Supporting Innovative Drug Discovery and Life Science Research (BINDS)] from Japan Agency for Medical Research and Development (AMED) (grant No. JP25ama121054).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2026-1-0218/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. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Kagoshima University Hospital Ethics Committee (No. 210265). Given the retrospective design, written informed consent was waived, and an opt-out procedure was provided (research participants and their relatives could opt out via the institutional website).

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/.

References

1. Ginsberg RJ, Rubinstein LV. Randomized trial of lobectomy versus limited resection for T1 N0 non-small cell lung cancer. Lung Cancer Study Group. Ann Thorac Surg 1995;60:615-22; discussion 622-3.
2. Jeon YJ, Shin S, Kong S, Yang S, Cho JH, Kim HK, Shim YM, Kang D, Park HY. Lobe-Specific Variability in Postoperative Pulmonary Function in Lung Cancer Patients: A Longitudinal Analysis and Comparison With Traditional Predictive Models. Respirology 2026;31:62-72. [Crossref] [PubMed]
3. Yokoba M, Ichikawa T, Harada S, Naito M, Sato Y, Katagiri M. Postoperative pulmonary function changes according to the resected lobe: a 1-year follow-up study of lobectomized patients. J Thorac Dis 2018;10:6891-902. [Crossref] [PubMed]
4. Nilssen Y, Brustugun OT, Fjellbirkeland L, Helland Å, Møller B, Wahl SGF, Solberg S. Distribution and characteristics of malignant tumours by lung lobe. BMC Pulm Med 2024;24:106. [Crossref] [PubMed]
5. Ueda K, Tanaka T, Hayashi M, Tanaka N, Li TS, Hamano K. Clinical ramifications of bronchial kink after upper lobectomy. Ann Thorac Surg 2012;93:259-65. [Crossref] [PubMed]
6. Yanagihara T, Sekine Y, Sugai K, Kawamura T, Maki N, Saeki Y, Kitazawa S, Kobayashi N, Kikuchi S, Goto Y, Ichimura H, Sato Y. Risk factors of middle lobe bronchus kinking following right upper lobectomy. J Thorac Dis 2021;13:3010-20. [Crossref] [PubMed]
7. Mizukami Y, Takahashi Y, Maki R, Adachi H. Risk factors for atelectasis of the middle lobe after right upper lobectomy: preoperative bronchial diameter and stapling of the fissure. J Thorac Dis 2021;13:5649-57. [Crossref] [PubMed]
8. Koike S, Eguchi T, Matsuoka S, Takeda T, Miura K, Shimizu K, Hamanaka K. Impact of counterclockwise rotation of the right middle lobe following right upper lobectomy. Interact Cardiovasc Thorac Surg 2022;34:1062-70. [Crossref] [PubMed]
9. Masuda Y, Marutsuka T, Suzuki M. A risk factor for kinked middle lobar bronchus following right upper lobectomy. Asian Cardiovasc Thorac Ann 2014;22:955-9. [Crossref] [PubMed]
10. Arai H, Tajiri M, Masuda H, Sekine A, Okudela K, Komatsu S, Iwasawa T, Masuda M. Intermediate bronchial kinking after right upper lobectomy for lung cancer. Asian Cardiovasc Thorac Ann 2021;29:19-25. [Crossref] [PubMed]
11. Ohtaka K, Ohtake S, Fujiwara-Kuroda A, Narita S, Otsuka S, Yamasaki H, Sasaki A, Shiiya H, Ujiie H, Aragaki M, Kato T. The role of the stapled interlobar fissure position for intraoperative detection and postoperative diagnosis of middle lobe torsion after right upper lobectomy. J Thorac Dis 2025;17:1268-77. [Crossref] [PubMed]
12. Yanagihara T, Ichimura H, Kobayashi K, Sato Y. Computed tomography detection of stapled interlobar fissure facilitates diagnosing postoperative lobar torsion: A case report. Int J Surg Case Rep 2017;41:86-8. [Crossref] [PubMed]
13. Higashiyama M, Takami K, Higaki N, Kodama K. Pulmonary middle lobe fixation using TachoComb in patients undergoing right upper lobectomy with complete oblique fissure. Interact Cardiovasc Thorac Surg 2004;3:107-9. [Crossref] [PubMed]
14. Wong PS, Goldstraw P. Pulmonary torsion: a questionnaire survey and a survey of the literature. Ann Thorac Surg 1992;54:286-8. [Crossref] [PubMed]
15. Higashiyama M, Tokunaga T, Kusu T, Ishida H, Okami J, Kodama K. Prophylactic middle lobe fixation for postoperative pulmonary torsion. Asian Cardiovasc Thorac Ann 2017;25:41-6. [Crossref] [PubMed]
16. Han DJ, Ok YJ, Oh SJ, Choi JS, Seong YW, Moon HJ. Interfissural Fixation of the Right Middle Lobe after Video-Assisted Thoracic Surgery Right Upper Lobectomy: Bronchial Anatomical Changes and Efficacy in Preventing Torsion. J Chest Surg 2024;57:477-83. [Crossref] [PubMed]