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Introduction

The operative modes for pulmonary parenchymal resection include pneumonectomy, bilobectomy, lobectomy, segmental resection (segmentectomy), and wedge resection, according to the extent of lung parenchyma to be resected. From the perspective of the technical features at the pulmonary hilum, these may be divided into anatomic (pneumonectomy, bilobectomy, lobectomy, and segmentectomy) and nonanatomic (wedge) resections. In anatomic resection, the extent of pulmonary parenchyma for resection is determined according to the extent of perfusion of pulmonary vessels as well as by the extent of aeration of the bronchi, which are divided at the hilum. On the other hand, in nonanatomic resection, the extent of parenchymal resection is determined solely according to the location of the target lesion. Although segmentectomy and wedge resection are both referred to as sublobar resection, their technical characteristics are quite different.

Almost 70 years ago, Churchill and Belsey introduced segmental resection as “segmental pneumonectomy” for treating benign lung diseases. In 1973, Jensik and colleagues suggested that anatomic pulmonary segmentectomy may be applied effectively to small primary lung cancers when the surgical margins are sufficient. Some subsequent nonrandomized studies showed that excellent outcomes may be achieved with segmental resection in patients with early cancers. These reports stimulated a debate regarding the optimal resection technique for early-stage non–small cell lung cancer, which was addressed in a prospective, randomized trial conducted by the Lung Cancer Study Group (LCSG). Limited pulmonary resection, including anatomic segmentectomy and nonanatomic wide wedge resections, was compared with lobectomy for stage IA lung cancer with regard to postoperative prognosis and pulmonary function. This study solidified lobectomy as the procedure of choice for treating this disease, based on the inferior postoperative survival and increased locoregional recurrence in the limited resection group. This randomized trial is still the only one that directly compared limited resection with lobectomy; therefore, the gold standard for lung cancer is still lobectomy.

In recent years, however, many smaller and pathologically earlier lung cancers have been seen in clinical practice, especially in Japan and the United States, and improvements in CT image quality, the widespread adoption of CT screening programs for lung cancer, and changes in the etiologic factors of lung cancer may underlie this phenomenon. Among the lesions specifically found in this context, the nonsolid lesion referred to as ground glass opacity (GGO) is a newly established clinical entity that may be a candidate for limited pulmonary resection. The term GGO is used to describe noncalcified, subsolid nodules, and the pathobiological nature, natural history, and proper management of GGOs have become matters of greater concern among thoracic surgeons. According to recent studies on the relationship between their appearance in CT images and histopathology, a considerable percentage of these lesions, although not all, are preinvasive, noninvasive, early forms of neoplastic growth, especially those of adenocarcinoma lineage (nonmucinous bronchioloalveolar carcinoma [BAC]), or minimally invasive adenocarcinoma. Thus, for smaller, earlier lung cancers, including GGO-BACs, the indications for segmentectomy are being revised, and recent nonrandomized studies have reported excellent survival.

Randomized clinical trials with peripheral lung cancers no more than 2 cm in diameter as the target lesions were begun in the United States (Cancer and Leukemia Group B) and Japan (Japan Clinical Oncology Group) around the same time. Case accrual and the maturation of prognostic data are eagerly awaited.

Figure 16.1
figure 1

Concept of ‘classic (conventional)’ segmental resection (segmentectomy). According to the classic (conventional) concept of segmental resection, the segmental artery and bronchus, which run parallel, are both divided at the pulmonary hilum, while the intersegmental vein, which runs on the intersegmental plane, is carefully preserved only by cutting the branches to the resected segment

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Figure 16.2
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Concept of “modified (easy)” segmental resection (segmentectomy). In the modified concept of segmental resection, the entire segmental artery, vein, and bronchus are divided at the hilum. In this case, it is not necessary to expose the intersegmental vein on the intersegmental plane; therefore, it becomes easier to maneuver with staplers in dividing the intersegmental parenchyma. This modified technique may be justified not only because of the easy maneuverability but also because of the anatomic considerations with regard to the lymphatics in the lung parenchyma, especially in malignant cases

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Figure 16.3
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Network of lymphatics around the intersegmental vein and beneath the pleura. Surgeons who perform segmental resection should be familiar with the anatomy of lymphatics in the lung, because these are one of the main routes for the drainage of malignant cells to develop into lymph node metastases. In performing lobectomy, surgeons are not concerned about the intrapulmonary lymphatics, because these systems are resected en block together with the tumor-bearing lobe. However, in dissecting the lung parenchyma between neighboring segments, surgeons should be aware of the dense network of lymphatics around the intersegmental vein. To preserve these veins essentially means to preserve the lymphatics, which might possibly contain malignant cells, as well. Therefore, a careful and prudent approach might be required to preserve the intersegmental vein

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Figure 16.4
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Factors closely related to local recurrence in segmental resection. How to divide the intersegmental lung parenchyma is another debate with regard to the technical aspects of segmental resections. Although any one of the methods—such as finger fracturing, electrocautery, or stapling—may be chosen, surgeons should be concerned about the tumor–surgical margin distance in relation to the local recurrence. Local recurrence on the segmental plane is most influenced by distance, not by the method for dividing the intersegmental parenchyma

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Figure 16.5
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Ligation of the superior segmental artery. There have been several variations in the technical aspects of segmentectomy, especially with regard to the method for transecting the lung parenchyma on the intersegmental plane (finger fracture versus electrocautery versus stapling) and for preserving the intersegmental pulmonary vein. In the conventional technique, the principle of segmentectomy includes parenchymal dissection that exposes the veins in the intersegmental plane and division of its branches coming from the resected segment. However, in the presence of dense lymphatic networks along with intersegmental veins, which might be a drainage route for malignant cells, preserving the intersegmental vein might not be desirable in terms of curability. Presently, the most popular approach to segmental resection is the standard lateral thoracotomy position using general anesthesia with the ability to provide single-lung ventilation. There is not much difference between the procedure for superior segmentectomy on the left side and that on the right; the right-sided procedure is described here. The first step of this procedure is accessing the pulmonary artery through the major fissure between the upper and lower lobes, followed by division of the segmental artery, bronchus, and vein, and transection on the intersegmental plane. The technique for reaching the intermediate pulmonary artery trunk between the upper and lower lobes in segmentectomy is essentially the same as the one for lobectomy. Usually, the intermediate pulmonary artery trunk is accessed directly by dividing the visceral pleura and underlying parenchyma. The anatomy of the intermediate pulmonary artery trunk is then carefully inspected to confirm the branching of the segmental arteries. Rarely, the branches to the superior segment (lower lobe) and posterior segment (upper lobe) share a common trunk, whereas two separate branches to the superior segment originate from the intermediate trunk. The segmental branch is carefully tied and divided

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Figure 16.6
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Division of the superior segmental bronchus. If the loose connective tissue around the intermediate pulmonary artery trunk and intermediate bronchial trunk is cleared away, it should be possible to adequately expose the root of the superior segmental bronchus. It should be taped and clamped for testing to confirm the extent of collapse (superior segment) by positive pressure ventilation. It may be necessary to confirm the superior segmental bronchus by intraoperative bronchoscopy. The superior segmental bronchus is divided by knife; the proximal bronchial stump may be closed by any method, such as simple ligation, suturing (3-0, 4-0 Prolene), or ligation

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Figure 16.7
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Estimation of the intersegmental plane by inflation of the entire lower lobe. Ventilation is performed as soon as the bronchus has been transected and the segmental boundary between the basal and superior segments has been roughly identified, because only the parenchyma of the basal segments is aerated. The intersegmental line on the pleural surface is marked by making small cauterized spots on the visceral pleura. In some cases, however, the boundary between neighboring segments is difficult to recognize even after positive pressure aeration

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Figure 16.8
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Estimation of the intersegmental plane by inflation of the posterior segment only using high-frequency jet ventilation. Alternatively, Okada and colleagues used a high-frequency jet ventilation method to visualize the extent of the superior segment. After the entire lower lobe is collapsed, air is passed through the cut end of the superior segmental bronchus by high-frequency jet ventilation, and only the area within the confines of the superior segment is inflated. By this selective ventilation, the superior segment pops up from the collapsed basal segment, where the boundary is the “inflation–collapse line,” an intersegmental plane between the superior and basal segments

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Figure 16.9
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Ligation of the superior segmental vein (I). The incisional line on the mediastinal pleura already made posterior to the hilum is extended further toward the pulmonary ligament to expose the root of the entire inferior pulmonary vein. As discussed previously, the caudal intersegmental branch of the three branches arising from the superior segmental vein must be exposed and left on the intersegmental plane according to the principle of classic segmentectomy. However, the method that sacrifices all the branches of the superior segmental vein is employed here to remove all the lymphatic systems in this segment. Again, the superior segmental vein, located cranially, is distinguished from the basal segmental vein. This vein is ligated and then divided, or stapled. The dotted line indicates the intersegmental branch (this is on the intersegmental plane) between the superior and basal segments

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Figure 16.10
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Ligation of the superior segmental vein (II). In this type of segmental resection, the whole superior segmental vein is ligated and divided. Careful inspection should be done to correctly identify the superior segmental vein

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Figure 16.11
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Mobilization of the superior segment from the intermediate and lower bronchi. All the vessels and the bronchus belonging to the superior segment are now divided or stapled. To ensure stapling occurs on the proper intersegmental plane, the basal segment should be aerated again by positive pressure ventilation, and proper marking on the intersegmental line should be confirmed. Before the intersegmental lung parenchyma is divided, mobilization of the superior segment away from the intermediate and lower lobe bronchi is recommended to create a gap for easier insertion of the staplers (arrow). This procedure might prevent the staplers from accidentally biting the intermediate pulmonary artery and bronchi

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Conclusion

Parenchyma-sparing, limited resections are becoming increasingly important in an era in which smaller and earlier lung cancer commonly is found in elderly patients with compromised conditions. Although lobectomy and pneumonectomy remain the mainstay for surgically treating lung cancer after the North American randomized trial in the 1980s, the surgical community must recognize the necessity of reevaluating the technical and prognostic aspects of the sublobar resection in the modern situation. Almost 30 years have passed since the only landmark randomized study, and the workup of patients, as well as their surgical care, has changed drastically.

The controversy regarding limited resection includes the demonstration of the equivalence of prognosis and the functional advantage of sublobar (segmental) resection in terms of pulmonary function versus standard lobectomy. The direct comparison between surgery and sophisticated radiologic techniques such as stereotactic body radiation therapy is another important and interesting issue, although the appropriate “surgery (mode of resection)” in this comparison must be clearly defined.

The technical standardization of the segmental resection, especially regarding the management of intersegmental parenchyma and vein from an oncologic perspective, needs to be addressed in the surgical community. The morbidity due to sublobar resection, such as prolonged air leakage, must be overcome, because these complications necessitate a longer hospital stay.