Abstract
Background
The demand for segmentectomy is increasing owing to its favorable long-term outcomes. Preservation of the lung parenchyma through segmentectomy may contribute to long-term survival; however, the morphological changes occurring in the residual lung parenchyma after segmentectomy are not fully understood. Low attenuation volume (LAV) is known as an indicator of emphysematous changes and has been used for morphological analysis of the lungs. This study aimed to investigate the postoperative changes in the residual lung after both lobectomy and segmentectomy and to evaluate the LAV in relation to the number of resected subsegments.
Methods
We included 56 patients who had undergone lobectomy or segmentectomy for non-small cell lung cancer or other lung diseases between April 2020 and November 2021, and high-resolution computed tomography preoperatively and postoperatively within 6 months. Three-dimensional reconstruction images were created to calculate the LAV and the percentage of low attenuation volume-to-lung volume (LAV%). The variables of the ipsilateral residual lung lobes, excluding the affected lobe, were evaluated for all patients pre- and postoperatively. The relationship between radiological parameters and the number of resected subsegments was examined. A comparative analysis was conducted by dividing the patients into two groups, with a threshold of the change in LAV% (ΔLAV%) ≥0.7% used to indicate hyperinflation using a receiver operating characteristic curve analysis: SS ≤5 group, those with ≤5 resected subsegments (n=32); and SS ≥6 group, those with ≥6 resected subsegments (n=24).
Results
The median age was 73 years, and 30 patients underwent segmentectomy. All 56 patients had a significant postoperative increase in lung volume but no significant increase in LAV or LAV% in the ipsilateral residual lung lobes (pre- and postoperative median lung volume: 1,130 vs. 1,261 mL, P<0.01; median LAV, 10.2 vs. 8.14 mL, P=0.54; median LAV%, 0.83% vs. 0.56%, P=0.10, respectively). The correlation analysis showed a weak but significant correlation between ΔLAV% and the number of resected subsegments (R=0.30, P=0.02). Significant increases in the change in LAV (median: SS ≤5, −0.68 mL; SS ≥6, 2.17 mL; P=0.04) and ΔLAV% (median: SS ≤5, −0.26%; SS ≥6, 0.0065%; P=0.01) were observed in the SS ≥6 group, but no significant increase in the change in lung volume in the ipsilateral residual lung lobes was observed compared with that in the SS ≤5 group (median: SS ≤5, 130 mL; SS ≥6, 335 mL, P=0.08). The postoperative pulmonary function was not significantly different between the two groups.
Conclusions
The number of resected subsegments correlated positively with ΔLAV%. An increase in ΔLAV% was frequently observed in patients in the SS ≥6 group. This suggests that hyperinflation can be induced after extensive lung resection, whereas it was rarely observed after limited resection, which could preserve normal lung parenchyma.
Keywords: Compensatory lung growth (CLG), low attenuation volume (LAV), lung cancer, segmentectomy
Highlight box.
Key findings
• The number of resected subsegments increased, the change in the percentage of low attenuation volume (LAV)-to-lung volume (LAV%) preoperatively and postoperatively increased. An increase in the change in LAV% was frequently observed in patients who underwent extensive lung resection with ≥6 subsegments compared with patients who underwent limited resection with ≤5 subsegments.
What is known and what is new?
• Several studies have shown that the preservation of lung parenchyma through segmentectomy may contribute to favorable long-term survival. However, the morphological changes in the residual lung parenchyma after lung resection, including lobectomy and segmentectomy, are not fully understood.
• Extensive lung resection may induce hyperinflation in the residual ipsilateral lung parenchyma, as shown using parameters such as lung volume and LAV in three-dimensional reconstruction images from high-resolution computed tomography.
What is the implication, and what should change now?
• Hyperinflation can be induced after extensive lung resection with ≥6 subsegments, whereas it was rarely observed after limited resection, which could preserve normal lung parenchyma. Postoperative pulmonary function tests show no difference between extensive and limited resection; however, limited resection that preserves lung parenchyma may maintain the ideal morphology of the residual lungs.
Introduction
The demand for pulmonary segmentectomy has been increasing as a result of trials reporting improved long-term survival following sublobar resection (1,2). These trials showed non-inferiority of long-term survival after sublobar resection compared to lobectomy for patients with small-sized peripheral non-small cell lung cancer (NSCLC). In contrast, only a 2–3% difference in postoperative pulmonary function was reported between sublobar resection and lobectomy (1,2), potentially suggesting a compensatory response of the residual lobes after lobectomy (3-7). While there is no definitive explanation for the favorable long-term outcomes after segmentectomy compared to lobectomy, the authors speculated that preservation of the lung parenchyma may allow more aggressive treatment for future lethal diseases, leading to greater overall survival (OS) after segmentectomy (1). The lung parenchyma preserved by segmentectomy may sustain defensive capability in the long-term even if this is not reflected in the preservation of postoperative pulmonary function. Therefore, we hypothesized that morphological differences in the residual lungs between lobectomy and segmentectomy may attribute more advantageous OS after segmentectomy. Various studies have reported morphological changes in the residual lungs post-lobectomy (3-7); however, morphological changes in preserved lung parenchyma and their effect on prognosis after segmentectomy remain unclear.
Low attenuation volume (LAV) is known as an indicator of emphysematous changes and defined as a three-dimensional (3D) region showing an attenuation value <−950 Hounsfield units (HU) on high-resolution computed tomography (HRCT) (8). LAV has been widely used in pulmonary morphological analyses, especially in patients with chronic obstructive pulmonary disease (COPD) (9-12). However, few studies have investigated changes in LAV pre- and post-lung resection. Therefore, this study aimed to elucidate the morphological changes in the residual lung post-pulmonary resection including lobectomy and segmentectomy, to compare the changes of LAV in relation to the number of resected subsegments, and to discuss the morphological effect in the preserved lung parenchyma, which may be related to compensatory lung growth (CLG) post-lung resection. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1786/rc).
Methods
Study design and patient selection
This retrospective study comprised patients who had undergone lobectomy or segmentectomy for NSCLC and other lung diseases at the International University of Health and Welfare Narita Hospital between April 2020 and November 2021. We excluded patients who had not undergone a non-contrast HRCT and spirometry both preoperatively and at 3–6 months postoperatively. Patients who had contralateral lung resection within 6 months after initial surgery were also excluded. The clinical data of the included patients were obtained through a retrospective chart review. Regarding the surgical technique for segmentectomy, the intersegmental plane was identified using the inflation-deflation method or near-infrared thoracoscopic imaging with intravenous indocyanine green administration, followed by intersegmental dissection, mainly using staplers. Thirty-day postoperative complications were retrospectively reviewed and evaluated using the Clavien-Dindo classification (13). This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of International University of Health and Welfare Narita Hospital (No. 24-CN-018). The requirement for written informed consent from each patient was waived owing to the study’s retrospective design.
Morphological analysis
This study obtained data concerning patients with non-contrast computed tomography (CT) scans (slice thickness, 1.0 mm), acquired at International University Health and Welfare Narita Hospital, using Aquilion ONE Prism edition and Aquilion Prime SP (Canon Medical Systems, Tochigi, Japan) software. The entire chest was scanned during inspiratory breath-hold with 0.5 mm × 80 mm detector collimation and a helical pitch of 65.0 using automatic exposure control at 120 kVp. REVORAS® (Ziosoft, Tokyo, Japan), a novel volume-rendering 3D image reconstruction software, was used for 3D image reconstruction from HRCT. All CT imaging data in AiCE Body Sharp (Canon Medical Systems) condition were utilized for 3D reconstruction. After excluding the soft tissues surrounding the lungs, as well as the large vessels and interstitial tissues within the lungs, morphological parameters were calculated, including lung volume, LAV, and the percentage of low attenuation volume-to-lung volume (LAV%). LAV was defined as regions showing <−950 HU on HRCT (8). The terms Δvolume, ΔLAV, and ΔLAV% were defined as the changes in lung volume, LAV, and LAV% pre- and postoperatively, respectively, which were calculated as postoperative values minus preoperative values.
The relationship between the parameters of the ipsilateral residual lung lobes and the number of resected subsegments was examined. The affected residual lobe after segmentectomy was not included in the analysis to exclude the effects of surgical manipulation and partial atelectasis associated with lung parenchymal resection during segmentectomy as presented (14). For example, in the case of right lower lobectomy, parameters were calculated for the right upper and middle lobes. In the case of left upper division segmentectomy, parameters were calculated only for the left lower lobe, without the lingular segment. Patients with tumor-induced atelectasis in other tumor-free lobes were excluded.
Pulmonary function analysis
Preoperative forced vital capacity (FVC), percentage of the actual FVC to the predicted FVC (%FVC), forced expiratory volume in 1 second (FEV1), percentage of the actual FEV1 to the predicted FEV1 (%FEV1), and FEV1/FVC were examined. A postoperative pulmonary function test was performed within 3–6 months postoperatively. Changes between the preoperative and postoperative pulmonary function tests were defined in terms of ΔFVC, ΔFEV1, Δ%FVC, and Δ%FEV1, and statistical analysis of each value was performed.
Comparison between limited and extensive resection
We divided the patients into two groups: SS ≤5 group, those with ≤5 resected subsegments; SS ≥6 group, those with ≥6 resected subsegments. The cutoff value of the number of resected subsegments was determined using a receiver operating characteristic (ROC) curve and dichotomized as follows: SS ≤5 group indicating postoperative non-hyperinflation with ΔLAV% <0.7% and SS ≥6 group indicating postoperative hyperinflation with ΔLAV% ≥0.7%. The area under the curve was 0.721 (95% confidence interval of 0.581–0.861). We based the 0.7% threshold on a previous study that reported that a preoperative LAV% of the total lung ≥0.7% was a risk factor for postoperative respiratory complications (15). Clinical and morphological variables were compared between the two groups to explore differences, with one group representing a limited resection and the other group representing an extended resection.
Statistical analysis
Descriptive statistics for continuous variables were reported as medians and ranges, and categorial variables were reported as frequencies and percentages, as appropriate. Spearman correlation analysis was conducted to assess the relationship between radiological parameters and the number of resected subsegments. Continuous and categorical variables were compared using Mann-Whitney U and Fisher’s exact tests, respectively, with statistical significance set at P<0.05. Comparisons of variables in the same patients pre- and postoperatively were performed using Wilcoxon signed-rank test. Statistical analysis was conducted using EZR software (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria).
Results
Patient characteristics
The patients’ characteristics are shown in Table 1. Thirty-one patients were men, and the median age was 73 years. Among the 56 patients, 49 were diagnosed with NSCLC. Other lung diseases included pulmonary aspergillosis, granulomatous inflammation, and focal lymphocyte infiltration. Sixteen patients had COPD and one patient had interstitial pneumonitis.
Table 1. Patient characteristics.
| Category | Values |
|---|---|
| Sex (men/women) | 31/25 |
| Age (years) | 73 (45–85) |
| Smoking index (pack-year) | 11.5 (0–104) |
| Body mass index (kg/m2) | 22.3 (15.4–31.1) |
| Procedure (lobectomy/segmentectomy) | 26/30 |
| Approach (hybrid VATS/complete VATS/thoracotomy) | 50/1/5 |
| FVC (L) | 2.89 (1.60–4.75) |
| FVC% (%) | 99.9 (65–135.7) |
| FEV1 (L) | 2.07 (1.10–3.41) |
| %FEV1 (%) | 90.2 (51.4–126.8) |
| FEV1/FVC (%) | 72.9 (42.7–97.1) |
| Disease (lung cancer/metastasis/inflammation/others) | 49/1/2/4 |
| Time to CT after surgery (days) | 178 (82–232) |
Data are expressed as n or median (range). CT, computed tomography; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; VATS, video-assisted thoracic surgery.
Surgical procedures for each patient are listed in Table 2. A total of 26 patients underwent lobectomy, one patient underwent bilobectomy, and 30 patients underwent segmentectomy. Simple (S6, upper division, lingular, and basilar segmentectomy) and complex segmentectomy (the others) were performed in 14 and 16 patients, respectively. Almost all patients underwent hybrid video-assisted thoracic surgery, and five patients underwent thoracotomy. The 56 enrolled patients were divided into two groups based on the number of resected subsegments (SS ≤5 group, n=32; SS ≥6 group, n=24), as determined using ROC curve analysis.
Table 2. Breakdown of surgical procedures.
| Surgical procedures | Segment | Value, n [%] |
|---|---|---|
| Lobectomy | 26 [46] | |
| Right | RUL | 6 [11] |
| RML | 5 [9] | |
| RLL | 3 [5] | |
| RUL + RML | 1 [2] | |
| Left | LUL | 5 [9] |
| LLL | 6 [11] | |
| Segmentectomy | 30 [54] | |
| Right | S1 | 3 [5] |
| S2 | 4 [7] | |
| S3 | 1 [2] | |
| S6 | 2 [4] | |
| S10 | 1 [2] | |
| S7a + S10 | 2 [4] | |
| S8 + S9 | 2 [4] | |
| S9 + S10 | 1 [2] | |
| S7 + S8 + S9 + S10 | 1 [2] | |
| Left | S1+2 + S3 | 1 [2] |
| S4 + S5 | 2 [4] | |
| S1+2ab | 1 [2] | |
| S6 | 7 [13] | |
| S8 + S9 | 1 [2] | |
| S8 + S9 + S10 | 1 [2] |
LLL, left lower lobectomy; LUL, left upper lobectomy; RLL, right lower lobectomy; RML, right middle lobectomy; RUL, right upper lobectomy.
Morphological analysis
In the analysis of morphological parameters for all 56 patients, a significant difference was observed in lung volume; however, no significant differences between pre- and postoperative values were observed in terms of LAV or LAV% in the ipsilateral residual lung lobes (Table 3). The correlation analysis showed that there was a weak but significant correlation between ΔLAV% and the number of resected subsegments (R=0.30, P=0.02). The number of resected subsegments increased, ΔLAV% increased; however, no such correlation was found among Δvolume, ΔLAV, and the number of resected subsegments (Figure 1).
Table 3. Lung volume and LAV changes of the residual lung lobe pre- and post-pulmonary resection.
| Category | Preoperative | Postoperative | P value |
|---|---|---|---|
| Lung volume (mL) | 1,130 (496–2,164) | 1,261 (343–2,675) | <0.01 |
| LAV (mL) | 10.2 (0–602) | 8.14 (0–655) | 0.54 |
| LAV% (%) | 0.83 (0–32.7) | 0.56 (0–34.8) | 0.10 |
Data are expressed as median (range). Wilcoxon signed-rank test was used. LAV, low attenuation volume; LAV%, percentage of low attenuation volume-to-lung volume.
Figure 1.
Correlation analyses between the radiological parameters and the number of resected subsegments. (A) ΔLung volume, (B) ΔLAV, (C) ΔLAV%. LAV, low attenuation volume; LAV%, percentage of low attenuation volume-to-lung volume; SS, subsegments.
The patient characteristics in the SS ≤5 and SS ≥6 groups are shown in Table 4. Lobectomy was significantly more frequent in the SS ≥6 group, but no differences were observed in terms of other clinical factors. The postoperative respiratory complications included prolonged air-leakage in 3, pneumonia in 2, chylothorax and lung hernia in each 1 in the SS ≤5 group, and pneumonia in 2 in the SS ≥6 group. The rate of surgery for upper lobe was slightly higher in the SS ≥6 group, but no significant difference was observed between the groups. The comparative analysis between the two groups showed no significant differences in pre- (Table 4) and postoperative lung volume, LAV, and LAV% in the residual lobes (Figure 2A-2C). In contrast, the SS ≥6 group showed significantly larger increases in both LAV and LAV% compared with the SS ≤5 group, despite no significant difference in the change in lung volume (Figure 2D-2F). Hyperinflation (ΔLAV% ≥0.7%) was significantly predominant in the SS ≥6 group (7 of 24 patients) compared with the SS ≤5 group (2 of 32 patients, P=0.03).
Table 4. Patients’ characteristics of SS ≤5 and SS ≥6 groups.
| Category | SS ≤5 (n=32) | SS ≥6 (n=24) | P value |
|---|---|---|---|
| Men | 15 (46.9) | 16 (66.7) | 0.18 |
| Age (years) | 74 [48–85] | 71 [45–84] | 0.13 |
| Smoking index (pack-year) | 3.75 [0–84] | 20.5 [0–104] | 0.23 |
| Body mass index (kg/m2) | 23.6 [15.4–31.1] | 22.3 [16.7–27.7] | 0.73 |
| Preoperative pulmonary function test | |||
| FVC (L) | 2.53 [1.86–4.75] | 3.02 [1.60–4.34] | 0.41 |
| %FVC (%) | 101 [65–136] | 99.2 [70.7–115] | 0.46 |
| FEV1 (L) | 1.88 [1.23–3.41] | 2.18 [1.10–3.39] | 0.36 |
| %FEV1 (%) | 95.2 [51.4–127] | 89.2 [67.2–119] | 0.47 |
| FEV1/FVC (%) | 73.0 [42.7–96.3] | 73.0 [59.1–97.1] | >0.99 |
| COPD (yes/no) | 10/22 | 6/18 | 0.77 |
| Procedure (lobectomy/segmentectomy) | 5/27 | 21/3 | 0.01 |
| Procedure for upper lobe (yes/no) | 11/21 | 13/11 | 0.18 |
| Respiratory complications (≥ grade 2/≤1) | 6/26 | 2/22 | 0.44 |
| Time to CT after surgery (days) | 175.5 [83–205] | 186 [82–232] | 0.10 |
| Morphological parameters of the target lobe | |||
| Lung volume (cc) | 781 [231–1,916] | 827 [460–1,324] | 0.52 |
| LAV (cc) | 3.26 [0.02–372.0] | 8.35 [0.22–293.2] | 0.11 |
| LAV% (%) | 0.41 [0–33.0] | 0.89 [0.03–22.2] | 0.13 |
Data are expressed as n (%), median [range], or n. COPD, chronic obstructive pulmonary disease; CT, computed tomography; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; LAV, low attenuation volume; SS, subsegments.
Figure 2.
Comparison of postoperative parameters of ipsilateral residual lobes between SS ≤5 and SS ≥6 groups. (A,D) Lung volume and Δlung volume, (B,E) LAV and ΔLAV, (C,F) LAV% and ΔLAV%. LAV, low attenuation volume; LAV%, percentage of low attenuation volume-to-lung volume; SS, subsegments.
Pulmonary functional analysis
Pulmonary function tests were performed at 3–6 months postoperatively. No significant difference was observed between the two groups in terms of pre- and postoperative %FVC and %FEV1 (Tables 4,5). Furthermore, changes in these parameters pre- and postoperatively were similar between the two groups (Table 5).
Table 5. Comparison of pulmonary function between SS ≤5 vs. SS ≥6 groups.
| Pulmonary function | SS ≤5 (n=32) | SS ≥6 (n=24) | P value |
|---|---|---|---|
| FVC (%) | |||
| Baseline | 101 (65.0, 136) | 99.2 (70.7, 115) | 0.46 |
| Postoperatively | 93.4 (44.5, 127) | 84.8 (56.4, 112) | 0.23 |
| Change from baseline | −11.0 (−50.8, 15.3) | −9.50 (−36.5, 6.30) | 0.60 |
| FEV1 (%) | |||
| Baseline | 95.2 (51.4, 127) | 89.2 (67.2, 119) | 0.47 |
| After surgery | 87.3 (41.5, 122) | 73.1 (45.5, 105) | 0.29 |
| Change from baseline | −7.95 (−26.0, 11.3) | −9.75 (−29.3, 11.8) | 0.28 |
Data are expressed as median (range). FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; SS, subsegments.
Discussion
This study investigated the postoperative morphological changes in residual lungs following anatomical resection, including both lobectomy and segmentectomy, based on the number of resected subsegments using 3D reconstructed image analysis. Our findings showed that there was a compensatory increase in lung volume in the ipsilateral residual lobes following pulmonary resections as previously reported (3-7). Notably, as the number of resected subsegments increased, the ΔLAV% also increased. Extensive pulmonary resection involving ≥6 subsegments showed significant morphological increases in ΔLAV and ΔLAV% in the ipsilateral residual lung compared with limited resection with ≤5 subsegments, while no significant differences were observed concerning postoperative changes in pulmonary function between the two groups. This suggests that hyperinflation may be induced after extensive lung resection, but less likely after limited resection, despite the change not affecting the postoperative pulmonary functional loss.
With advances in radiological lung morphological analysis, the LAV has been established as one of the most widely used quantitative evaluations of emphysema (8), predicting short- and long-term outcomes in patients with COPD (9-12). The percentage of LAV in terms of total lung volume is associated with FEV1 and diffusing capacity (9), and predict a rapid decline in FEV1 and high mortality in patients with COPD (10). The heterogeneous spatial distribution of the LAV can also negatively affect clinical and functional outcomes in patients with COPD, such as FEV1 (11) and its accelerated decline (12). LAV is also a reliable predictive marker of postoperative respiratory complications post-lobectomy (15-19). The preoperative LAV% is significantly higher in patients with postoperative respiratory complications compared with those with no complications (15-18). LAV% thresholds reportedly range from 0.7% to 1.1%, with a greater LAV% being associated with increased postoperative respiratory and cardiopulmonary complications (15-17), and a greater decline in postoperative function (19). Furthermore, a large preoperative LAV (defined as ≥5% to the total lung volume) has been demonstrated to be associated with shorter OS in patients with NSCLC treated by surgery (20). These cited studies indicate that increased LAV is associated with undesirable short- and long-term outcomes in patients with COPD or in those who have undergone pulmonary resection.
Lungs are not known to regenerate; however, the changes in the residual lung following major pulmonary resection can be attributed to CLG. CLG is defined as an increase in the amount of functional lung tissue in response to lung resection, injury, and disease, as observed in experimental small animal models (21). Whether CLG occurs in human adults remains controversial, because no technology exists to measure the exact weight or structure of the remaining lung in a living person. Radiologically estimated lung weight (ELW) may reflect CLG (3,4), which is calculated through multiplying the lung volume by the average radiological lung density, as determined using the formula (22): (mean HU +1,000)/1,000.
We previously reported a significant increase in the ELW of the residual lung post-lobectomy to compensate for the loss of lung parenchyma (3,4), and this finding was subsequently corroborated by other researchers (5,6). The ELW has been shown to increase more significantly in patients of younger age, and in those with a history of light or no smoking and major pulmonary resection (4-7), and correlates with the recovery of postoperative pulmonary function (7). Nonetheless, lobectomy increases the ELW (3-7) and lung volume (3-7,23) but decreases the average radiological lung density of the residual lungs (4). Mizobuchi et al. reported that the average radiological lung density similarly declined postoperatively in groups with either <10 subsegments or ≥10 subsegments resection (4), suggesting that the mean HU decreased owing to an increase in air per CT voxel, which may be because of hyperinflation of the residual lung post-lobectomy. While this result differs somewhat from our findings, we consider that this difference is likely to be a result of differing criteria for subsegment division. Our results showed that extended resection with ≥6 subsegments increased LAV in the residual lung more than that in patients with limited resection involving ≤5 subsegments.
It remains unclear whether the increase in LAV after pulmonary resection directly indicates emphysematous changes, similar to how emphysematous changes are evaluated in patients with COPD. Shikuma et al. evaluated the radiological parameters of the ipsilateral residual lung after lower lobectomy in healthy living lung transplantation donors (24). They measured the D value, which is considered to measure the structural quality of the lungs and to sensitively detect alveolar tissue destruction (25). Their results showed no change in structural quality pre- and post-lobectomy, despite significant increases in volume values, including total lung volume and LAV. This might suggest the occurrence of post-lobectomy CLG, not emphysematous change. However, they demonstrated that the percentage of middle attenuation volume (−700 to −950 HU), which indicates functional lung tissue, decreased significantly, albeit by a small margin of 0.3%, while the percentage of LAV increased by 1.8%, albeit not significantly. This increase in LAV accords with our results. While the increase in the proportion of LAV post-lobectomy was slight and may have little effect on healthy individuals, these postoperative morphologic changes may be an unfavorable compensation that imposes an excessive burden in older adult patients or those with pathological conditions, such as COPD and interstitial pneumonias, potentially affecting long-term outcomes.
CLG is considered to be associated with postoperative pulmonary function. A significant correlation was observed between the residual lung volume and the actual postoperative values of spirometry, which showed further improvement beyond the predicted values post-lobectomy (3-7,23,26). The postoperative pulmonary function post-lobectomy was comparable to that observed after lung parenchyma-preserving segmentectomy (7), supported by recent large-scale prospective clinical trials (1,2). A recent meta-analysis including lobectomy and segmentectomy reported that the postoperative FEV1 significantly increased compared with the predicted value for resections involving ≥3 segments, while the postoperative FEV1 was slightly lower than the predicted value for resections of <2 segments (26). These findings support our results, which showed no significant difference in spirometry between extended and limited resections with ≥6 and ≤5 subsegments, respectively. However, it remains uncertain whether the recovery from pulmonary function loss is a result of lung growth or reservoir use. Pulmonary function peaks in the early 20s and continues to decrease throughout adulthood (27). If the compensatory response of the residual lungs after lung resection mainly depends on reservoir use, it may be difficult to clinically respond to situations that require intensive treatments in the future because of insufficient reserve capability. This may be the significance of the preservation of lung parenchyma, which is not captured using postoperative spirometry.
This study has some limitations. It was a single-center retrospective study involving a small number of patients, which was attributable to the high rate of missing postoperative pulmonary function test data, resulting from the restrictions imposed during the coronavirus disease 2019 (COVID-19) pandemic. Diffusion capacity was also not measured in the pre- and postoperative pulmonary function tests, despite its potential relationship with LAV after lung resection. Furthermore, survival analysis could not be performed, because this cohort included patients with benign diseases in addition to those with NSCLC. A larger cohort clinical study is needed to determine the postoperative increase in the LAV after extensive resection and its effect on long-term outcomes. The timing of postoperative CT scans and pulmonary function tests ranged from 3 to 6 months after surgery, which may have influenced the results regarding the residual lung condition and postoperative pulmonary function. Longitudinal evaluations at later time points, such as at 12 months or later, are needed. The two patient groups could not be matched for the lobe site owing to significant variations among patients and to the small cohort size in this study. Since the lobe site to be resected and the presence of COPD can significantly influence compensatory morphological changes in the residual lungs and postoperative pulmonary function (20,23,28,29), a lobe-site-matched analysis with a larger cohort is therefore warranted. Additionally, this study lacked data on evaluating pulmonary blood flow. The postoperative ratio of the main pulmonary artery diameter to the ascending aorta diameter is reportedly larger after lobectomy than after segmentectomy (30), suggesting differences in blood flow changes between lobectomies and segmentectomies. However, whether these pre- and postoperative pulmonary blood flow changes affect morphological compensatory changes in the postoperative lung remains unclear. Finally, thoracoscopic surgery is reportedly associated with less postoperative pain and a better quality of life than thoracotomy (31). Although most of the patients in this study underwent hybrid VATS, the influence of the surgical approach on postoperative compensatory changes in the lungs cannot be ruled out.
Conclusions
The number of resected subsegments and ΔLAV% showed a positive correlation, and an increase in ΔLAV% was frequently observed in patients with extensive lung resection with ≥6 subsegments. This suggests that hyperinflation may be induced in the residual lung after extensive lung resection, whereas it was less likely observed after limited resection, where normal lung parenchyma could be preserved. This morphological change may affect the long-term outcomes after extensive resection, despite it not immediately affecting postoperative pulmonary function.
Supplementary
The article’s supplementary files as
Acknowledgments
We would like to thank Editage for English language editing. We would also like to acknowledge Mr. Daisuke Tomoshige and Ms. Mamiko Igarashi for their support in using REVORAS® (Ziosoft, Tokyo, Japan).
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 Institutional Review Board of International University of Health and Welfare Narita Hospital (No. 24-CN-018). The requirement for written informed consent from each patient was waived owing to the study’s retrospective design.
Footnotes
Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1786/rc
Funding: None.
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1786/coif). The authors have no conflicts of interest to declare.
Data Sharing Statement
Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1786/dss
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