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Segmentectomy
RATIONALE FOR SEGMENTECTOMY
Segmentectomy was first performed in 1939 for the treatment of benign pulmonary diseases such as bronchiectasis and tuberculosis. Shortly thereafter, anatomic pulmonary segmentectomy was also employed for primary lung cancers. The study by Jensik et al. in 1979 showed that segmentectomy was safe and feasible for selected patients with non-small-cell lung cancer (NSCLC). 1 Since then, whether segmentectomy is comparable to lobectomy has been an area of controversy.
In 1995, the Lung Cancer Study Group reported a randomized trial in stage IA (T1N0M0) NSCLC, comparing limited resection in 122 patients (82 segmentectomies and 40 wedge resections) with lobectomy in 125 patients. 2 The results showed that, compared with lobectomy, limited resection was associated with 75% increase in recurrence (p = .02), tripling of local recurrence (p = .008), 30% increase in overall death (p = .08), and 50% increase in cancer death (p = .09). The inclusion of nonanatomic wedge resections in the limited resection group tends to bias the results in favor of lobectomy and subsequent studies have not confirmed the results found in the Lung Cancer Study Group report. Thereafter, lobectomy has been considered the standard procedure for early stage NSCLC, while sublobar resection is reserved only for those who could not tolerate lobectomy due to marginal lung function and/or significant comorbidities. However, the size of the lesion to be resected should be taken into consideration, given that, in the seventh edition of the Union for International Cancer Control staging system for NSCLC, T1 disease is now subdivided into T1A (<2 cm) and T1B (>2 cm). 3 The Lung Cancer Study Group trial included all T1N0M0 tumors of size up to 3 cm, and it did not stratify the results between T1A and T1B. 2 In a more detailed retrospective study involving 1272 stage I NSCLC patients, the 5-year cancer-specific survivals were similar after lobectomy (92.4%) or segmentectomy (96.7%) when the tumor size was <20 mm. 4
It should also be noted that the Lung Cancer Study Group trial came from the time when only TNM (tumor node metastasis) staging was considered for surgical strategy. With the increased use of computed tomography (CT) screening, small peripheral ground glass opacity (GGO) lesions, which would have been difficult or even impossible to detect on routine chest X-ray, have been encountered more frequently in daily practice. These lesions often correspond to rather indolent early stage adenocarcinomas. Emerging data have shown that these GGO lesions seldom have lymphatic involvement. Compared with standard lobectomy, sublobar resection may offer equivalent local control and disease-free survival for these patients. The International Association for the Study of Lung Cancer, together with the American Thoracic Society and European Respiratory Society, recently proposed a new histologic classification system for lung adenocarcinomas, highlighted by the introduction of adenocarcinoma in situ (AIS; small adenocarcinomas <3 cm in diameter with pure lepidic growth) and minimally invasive adenocarcinoma (MIA; small solitary adenocarcinomas showing predominant lepidic growth with <5 mm invasion). 5 It is appropriate at this time to reevaluate the indication and selection of surgical approach and specifically, the extent of resection, incorporating both anatomical (TNM) and biological behavior (histologic subtyping) of the tumor.
Meanwhile, segmentectomy should be distinguished from nonanatomic wedge resection, as the latter was applied to up to one-third of the patients in the limited resection arm of the Lung Cancer Study Group trial. 2 The advantages of segmentectomy over nonanatomic wedge resection are at least twofold: first, by dissecting the segmental vessels and bronchus, hilar and segmental lymph nodes can be harvested systematically; second, anatomic segmentectomy also enables a deeper parenchymal resection and a safer margin for relatively centrally located lesions.
Moreover, surgical management of early stage lung cancer has changed greatly with the introduction of minimally
invasive video-assisted thoracoscopic surgery (VATS). 6 In the case of lobectomy, there is a large body of evidence demonstrating that VATS is associated with decreased morbidity and mortality, shorter hospital stay, less postoperative pain, earlier return to normal life, better quality of life, and superior compliance with adjuvant therapy. VATS even has potentially better oncologic results, making it now the preferred approach over open lobectomy. When segmentectomy is performed via VATS, it is not simply to revive a procedure that previously was used infrequently but to add new meaning to “minimally invasive” lung cancer surgery to include parenchymal sparing, in addition to the other advantages of VATS noted above. For small early stage lung cancers, VATS segmentectomy may be expected to achieve excellent oncologic results with very low morbidity and mortality. A retrospective study conducted at our hospital compared clinical outcomes between VATS segmentectomy and lobectomy in patients with small-sized (<2 cm) stage IA tumors. 7 There were no in-hospital deaths in either group. Local recurrence rates were similar after VATS segmentectomy (5.1%) and lobectomy (4.9%), and no significant difference was observed in 5-year overall or disease-free survivals following both procedures.
INDICATIONS FOR SEGMENTECTOMY
Pulmonary segmentectomy is often indicated for benign lesions such as those caused by infectious diseases, and may also be used selectively in patients with NSCLC. For small GGO lesions, segmentectomy is sometimes used to establish a histologic diagnosis, as fine needle biopsy has been shown to be quite unsatisfactory in such situations. The overall diagnostic yield from fine needle aspiration is merely 51% for GGO dominant lesions (GGO ratio >50%) and only 35% for GGO dominant lesions smaller than 10 mm. In addition, these lesions are sometimes extremely difficult to locate when using a VATS approach, making a wedge resection very challenging.
As mentioned earlier, segmentectomy has been accepted and used as an alternative for those high-risk lung cancer patients who are deemed unable to tolerate lobectomy. The potential benefits of segmentectomy compared with lobectomy are less surgical risk and better preservation of pulmonary function, while its advantage over nonanatomic wedge resection is superior oncologic outcome. Until recently, the indication for segmentectomy in good-risk patients who have no contraindication to lobectomy was not only unclear but questionable on oncologic grounds. Both tumor size and biology should be considered in determining the feasibility and efficacy of segmentectomy. Retrospective data from single or multiple institutions demonstrate that segmentectomy provides acceptable local control for tumors sized 2 cm or smaller, provided that at least a 2 cm resection margin can be achieved. 8 GGO-type tumors represent an excellent indication for segmentectomy. For pure GGO lesions corresponding to AIS or MIA, even tumors up to 3 cm can be considered for segmentectomy. A near 100% diseasefree survival rate can be expected after complete resection. 9
Several studies have shown that width of resection margin is an important factor in maintaining local control following segmentectomy. 7 A safe margin of greater than 2 cm might be reasonable, as resection margins less than 2 cm have been shown to be associated with an increased incidence of local recurrence. Based on this concern, if a tumor is located on the edge of diseased segment or a safe resection margin cannot be guaranteed intraoperatively, multiple segmental resections or lobectomy should be performed.
For lung cancer patients, preoperative staging should be completed to confirm the absence of nodal (mediastinal or hilar) disease. Small tumors, especially those appearing on CT to be air-containing lesions, are associated with a lower likelihood for lymphatic spread, which is another reason why they are excellent candidates for segmental resection. Still, careful intraoperative exploration of hilar and mediastinal lymph nodes should be performed to exclude occult metastases and ensure the appropriateness of segmentectomy. Conversion to standard lobectomy is indicated when a frozen section of a mediastinal or hilar lymph node demonstrates the presence of metastatic disease. Segmentectomy should be oncologically more effective than nonanatomic wedge resection, since it includes dissection of intersegmental, intralobar, and interlobar lymph nodes.
While anatomically less lung parenchyma is resected by segmentectomy than lobectomy, it does not necessarily result in a similar amount of pulmonary function preserved. This is affected by multiple factors, including the number, location, and quality of the segment resected. Resecting more than three segments has been shown to leave only 0.1 L of forced expiratory volume in 1 second in the remaining lobe. Recognizing this, basal segmentectomy of the lower lobes with preservation only of the superior segment, though technically feasible, is seldom indicated.
GENERAL STRATEGY FOR SEGMENTECTOMY
Technically, all segments can be approached surgically. The superior segments of the lower lobes, the lingular segment and the upper division of the left upper lobe, and posterior segment of the right upper lobe, in decreasing order of frequency, are the most common segmentectomies performed. Other individual segmental resections, such as upper lobe superior or anterior segmentectomy, are feasible but less commonly performed. Basal segmentectomy is seldom indicated, as it saves very little pulmonary function of the remaining lower lobe.
Segmentectomy can be performed thorough standard lateral thoracotomy or via a VATS approach. Compared with thoracoscopic lobectomy, VATS has been applied to anatomic segmentectomy only recently. Technically, thoracoscopic segmentectomy is considered to be more difficult than thoracoscopic lobectomy. Thoracic surgeons should be familiar with the three-dimensional anatomical relationship
of pulmonary segments to accomplish a segmentectomy successfully. Still, it has been proven to be safe and oncologically effective. No matter whether via an open or minimally invasive approach, it is imperative to make certain that standard dissection and oncologic principles are not compromised.
Open segmentectomies are often approached through a lateral thoracotomy via the fifth intercostal space. In performing a minimally invasive thoracoscopic segmentectomy, a standard threeor four-hole approach, with the major utility port in the fourth or fifth intercostal space, is the usual technique. The entire chest cavity should first be inspected to rule out signs of unexpected advanced disease, such as pleural dissemination or concomitant additional pulmonary nodules. Except for high-risk patients who cannot tolerate lobectomy, mediastinal or hilar nodal involvement should always lead to conversion to standard lobectomy, so as to ensure lymphatic clearance. Usually, the tumor should be palpated to confirm that segmentectomy is the correct procedure to ensure an adequate resection margin; otherwise, a bi-segmentectomy or lobectomy would be a better choice.
During segmentectomy, the segmental pulmonary veins, arteries, and bronchus are dissected and stapled separately. Thoracoscopic segmentectomy usually begins with identification and dissection of the segmental vein. Subsequently, the bronchus or the artery is divided, depending on the segment to be resected. Alternatively, the arterial branches can be identified and mobilized before the segmental veins are divided, but the more logical approach takes the segmental vein first. Some authors stated that this might minimize engorgement of the segment and facilitate further maneuvering, but in our experience, this has not been the case. Mobilizing arterial branches to the posterior segment of the upper lobes or the apical segment of the lower lobes often requires dissection of the major fissure. In the major fissure, the main pulmonary artery can be exposed, demonstrating its continuation into the lower lobe. On the right side, the lower lobe superior segmental branch can be identified at the posterior part of the major fissure. The posterior ascending and the middle lobe branches originate opposite each other, and go, respectively, to the posterior segment of the upper lobe and the middle lobe.
On the left side, the pulmonary artery crosses superiorly above the left main bronchus to become the most posterior structure in the hilum. The apicoposterior and anterior segmental branches are located anteriorly and superiorly. A separate posterior segmental branch is often found posteriorly on the main pulmonary artery, just at or above the major fissure. In the major fissure, the lingular branches, directed anteriorly, and the superior segment branch, posteriorly, are located across from each other on the continuation of the pulmonary artery. The surgeon must be mindful of the high variability in pulmonary artery branching, and carefully identify and confirm each branch before ligation.
In performing VATS segmentectomy, the pulmonary vessels are usually divided using endostaplers or endo-clips, with or without the help of energetic devices such as a Harmonic scalpel. After vascular division, the segmental bronchus is then identified and divided with an endostapler, or divided sharply and closed with interrupted absorbable sutures. The segmental bronchus is first clamped and the lung inflated before stapling for further confirmation of the correct anatomic location. Alternatively, a bronchoscopy can be helpful to confirm the correct segmental bronchus has been identified.
Division of the intersegmental plane is sometimes the most challenging part of a segmentectomy. Selected jet ventilation in the diseased segmental bronchus may help delineate the correct plane. 10 In our experience, identification of the intersegmental plane can be achieved by repeated ventilation of the ipsilateral lung after the segmental bronchus is clamped. The first several puffs will probably serve to delineate the parenchyma aerated by that bronchus. Due to the large degree of intersegmental cross-ventilation through collateral pores of Kohn, it may be helpful to inflate the entire lung, clamp the segmental bronchus, and then collapse the lung while observing the delineation between residually inflated and actively deflating lung. In addition, the divided vascular and bronchial structures can be used as landmarks to guide this process. There are two ways to divide the segmental parenchyma: via the so-called open division or with the use of a stapling device. The advantage of open division with electrocautery or simply by “stripping” the intersegmental plane using the venous supply as a guide, is greater preservation of lung volume. However, this technique is associated with increased risk of air leak and oozing from the raw surface of the lung, which could be problematic after operation, though both the air leak and bleeding usually stop spontaneously in a short period if the correct plane has been entered. Staple division results in a pneumostatic separation of the intersegmental plane, minimizing the troublesome issue of air leak, but this comes at the expense of more volume loss, as the visceral pleural layers are drawn together during the act of stapling. The intersegmental plane is stapled according to the inflation-deflation line and at least a 2 cm parenchymal resection margin should be guaranteed in segmentectomy for malignant diseases. When using staplers to divide the intersegmental plane, care should be taken to ensure they are placed exactly in the right position so as to avoid inadvertently stapling the adjacent segmental vein or bronchus. This may result in engorgement or atelectasis and repeated infection of the remaining lobe. Inflation of the remaining lung after the stapler is approximated but not yet fired is often helpful in avoiding inadvertent injury of the adjacent segmental bronchus.
SPECIFIC SEGMENTAL RESECTIONS
Upper division segmentectomy of the left upper lobe
This segmentectomy begins with the dissection of the anterior hilum. After the upper division branches of the left superior pulmonary vein are divided (see Figure 18.1), the upper division bronchus, located directly behind the pulmonary vein, is readily exposed (see Figure 18.2). Under thoracoscopy, this can easily be visualized. It is then divided
18.1
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