Segmentectomy for Primary Lung Cancer




Introduction



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Segmentectomy was initially described by Churchill and Belsey1 in 1939 for the treatment of bronchiectasis. Although the operation is still used to treat suppurative and other nonmalignant processes (e.g., aspergilloma, pulmonary sequestration), other pulmonary infections, pulmonary abscesses, and benign tumors of the lung (hamartomas, papillomas), this chapter concerns its controversial use in early-stage lung cancer.2 Until 1950, pneumonectomy was the standard of care for lung cancer. However, increasing awareness of the diminution of respiratory function caused by pneumonectomy soon led to interest in lobectomy and other lesser resections for tumors of amenable size and location. In 1973, Jensik et al.3 reported the first series of segmentectomies for early-stage lung cancer. Since then, limited resection for lung cancer has been a topic of much debate, and the controversy has been plagued by conflicting results between studies comparing segmentectomy and standard lobectomy or pneumonectomy.




General Principles



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Segmentectomy is an anatomic sublobar resection that involves the removal of functionally discrete units of the bronchovascular anatomy. The bronchovascular architecture is composed of a series of individual segments. Each segment has a pyramidal structure with its apex at the hilum and its base on the surface of the lung. Individually, the segments are supplied solely, with few collateral connections, by the following structures: (1) a segmental bronchus as a tertiary branch of the bronchial tree; (2) a segmental branch of the pulmonary artery (as well as the bronchial artery); and (3) a segmental (± intersegmental) branch of the pulmonary vein together with lymphatics. Each segment behaves as a discrete anatomical and functional unit that can be removed by segmental resection without affecting the functionality of the remaining lobe or adjoining bronchial segment. In properly selected patients with early-stage non–small-cell lung cancer (NSCLC), segmentectomy can achieve outcomes that are equivalent in overall survival to pneumonectomy and lobectomy.



A thorough knowledge of the human lung anatomy is mandatory for any surgeon undertaking this resection. There are 10 segments in the right lung (3 in upper lobe, 2 in middle lobe, and 5 in lower lobe) and 8 to 10 segments in the left lung (4–5 in upper lobe and 4–5 in lower lobe) (Fig. 73-1).




Figure 73-1


A schematic drawing of the different segments of the lungs. Note the right lung has 10 anatomical segments, whereas the left lung has 9 segments only. Anterior view of the distal trachea, carina, right and left bronchial trees. Right upper lobe segments: 1 apical; 2: anterior; 3: posterior. Right middle lobe segments: 4: lateral; 5: medial. Right lower lobe segments: 6: superior; 7: medial basal; 8: anterior basal; 9: lateral basal; 10: posterior basal. Left upper lobe segments: 1 and 3: apical posterior; 2: anterior; 4: superior lingular; 5: inferior lingular. Left lower lobe segments: 6: superior; 7 and 8: anteromedial basal; 9: lateral basal; 10: posterior basal. (Courtesy of Dr. Thomas W. Rice and Joseph A. Pangrace, Cleveland Clinic.)





Several operations fall under the umbrella of sublobar pulmonary resection. These are the wedge, the segmentectomy, and the extended segmentectomy. It is important to note that a wedge resection, sometimes called an atypical segmentectomy because of its sublobar resection status, is not an anatomical resection. Although sometimes preferred because it is less technically demanding than segmentectomy, the wedge resection is associated with numerous pitfalls, including a difficulty in obtaining or identifying a tumor-free resection margin, limited extent of lymph node sampling and excision, high rate of local recurrence, and diminished overall survival. Segmentectomy, on the other hand, respects anatomic barriers and is associated with better overall and disease-free survival. Extended segmentectomy describes the technique whereby the parenchyma is divided lateral to the intersegmental plane to accommodate a wider resection margin.




Patient selection



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Two groups of patients with NSCLC may benefit from segmentectomy, those who are able to tolerate lobectomy, but for whom curative resection is likely with a sublobar resection based on the small size of the tumor and negative nodes. The second group is those who are unable to tolerate lobectomy and for whom a lesser resection constitutes an alternative local cancer treatment. Patients with poor pulmonary reserve (forced expiratory volume in 1 second [FEV1] less than 50% of predicted) or with multiple resectable lesions may also be considered for a segmental resection if complete resection is likely.



Conventional fractionated radiation therapy has been the alternative local treatment for medically inoperable patients with early-stage NSCLC and is associated with modestly prolonged survival compared to observation. Recently, several nonsurgical treatments have become available, including stereotactic body radiation therapy (SBRT) and percutaneous ablative therapy including radiofrequency, cryotherapy, and microwave (Chapter 85). Although these treatments appear to decrease the risk of respiratory failure, disability, and death, there is currently little evidence of efficacy compared to a parenchymal-sparing surgical resection. In the few trials that are available, all nonoperative modalities have higher recurrence rates over shorter intervals. Currently, two ongoing randomized trials are investigating the value of SBRT versus sublobar resection or lobectomy.




Preoperative assessment



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Preoperative workup and evaluation for thoracic surgery is discussed elsewhere in this book in detail (see Chapter 4). The same principles apply for segmentectomy.



The presence of stage I NSCLC should be ensured preoperatively. Combined PET/CT scan is the best radiographic and metabolic test available for ruling out extrathoracic disease, assessing the mediastinal and hilar lymph nodes, and excluding other suspicious nodules in the lung. Endobronchial ultrasound (EBUS) and endoscopic esophageal ultrasound (EUS) are first-line tools for mediastinal staging and should be used followed by videomediastinoscopy to rule out false-negative results when suspicious-looking lymph nodes are detected on radiographic imaging. MRI of the brain with contrast should be considered in all patients with headache or other neurologic symptoms, since a brain metastasis cannot be visualized by PET/CT.



Medical operability should be checked in patients with poor performance status if any surgical procedure is being planned. Algorithms for differentiating risk levels for patients being considered for a lung resection have recently been published.4 These European guidelines provide cutoff values for subjecting at-risk patients to additional assessment and threshold values to differentiate low-risk from high-risk patients. Cardiology risk stratification and pulmonary function testing including the diffusion capacity of carbon monoxide for the lung (DLCO) are recommended in every patient undergoing pulmonary resection. Further exercise testing with oxygen consumption (VO2) should be performed in patients with FEV1 and/or DLCO <80%. Patients with VO2 max or a predicted postoperative (ppo) value below 10 mL/kg/min or 35% are not candidates for major anatomic resections. In patients with VO2 max values between 10 and 15 mL/kg/min or between 35% and 75%, ppo FEV1 and ppo DLCO should be calculated. If both values are >30%, resection can be performed up to the calculated extent. Otherwise, ppoVO2 max should be calculated.




Surgical Technique



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The patient is placed in lateral decubitus position and intubated under general anesthesia with a double-lumen endotracheal tube. An epidural catheter is placed for pain. The chest is usually entered through the fifth intercostal space or one rib higher if there is a concern for pathology at the lung apex. The operation can be performed using open or video-assisted thoracic surgery (VATS) technique. For the open procedure described later, we routinely perform a muscle-sparing posterolateral thoracotomy with division of the latissimus dorsi and mobilization and retraction of the serratus anterior (see Chapter 2).



After entering the chest, the hemithorax is inspected and lung palpated to rule out evidence of advanced disease that would preclude segmental resection. If there is any uncertainty about the preoperative diagnosis, tissue is obtained for frozen-section analysis before proceeding. Central lesions may be sampled via needle biopsy. Frozen sections then are obtained of N1 and N2. The presence of metastatic disease in any lymph node constitutes an indication to proceed with lobectomy,5 provided the patient is surgically fit based on the preoperative assessment. Frozen section of the resection margin is also recommended.6



Segmentectomy


Although any bronchovascular segment can be removed, certain operations are more commonly performed. These include taking or sparing the superior segment for lower lobe cancers and taking or sparing the lingula for left upper lobe cancers. It is generally easier to remove the superior segment of the lower lobe (S6), the lingular segments (S4 + S5), and the basilar segments of the lower lobe (S7–S10), whereas the individual segments in the upper lobe (S1, S2, S3) and lower lobe (S7, S8, S9, S10) are more challenging. Although the spatial approach and the order of dividing the individual bronchovascular structures may vary depending on the individual segment(s), the overall principles remain the same.



Regardless of which segment is being resected, the fissure is opened first to reveal the pulmonary arterial branch. The appropriate segmental artery(ies) are identified and divided in the usual manner to expose the underlying segmental bronchus. Gentle traction on the segment with an atraumatic clamp may help to expose segmental branches that are hidden deep within the lung parenchyma (Fig. 73-2).




Figure 73-2


Traction on the segment itself can aid in identifying the appropriate arterial branches and segmental bronchus.





The S4, S5, and S6 segments each have an individual central vein that can be ligated or clipped, whereas the veins in other segments run close to the periphery and cannot be identified until dissection of the intersegmental plane has commenced and drainage into the superior or inferior venous trunks becomes visible. In some cases, early division of the individual central segmental vein can facilitate visualization of the pulmonary artery. However, these veins cannot be identified upon stapling of the parenchyma, so it is important to identify the anatomy of the venous trunks carefully before dividing the segmental vessels to avoid inadvertent ligation of veins draining blood from adjacent segments. This may result in venous thrombosis, lobar infarct, and potentially disastrous complications postoperatively.



Intraoperative bronchoscopy can be very helpful if there is confusion regarding the segmental anatomy or concern about potential compromise of the adjacent segmental bronchial orifice. A pediatric bronchoscope fits easily through the lumen of a double-lumen endotracheal tube to reveal the endobronchial view. In addition, the light on the scope illuminates the airway which can be visualized from the operative field.



Before dividing the parenchyma, it can be difficult to identify the appropriate plane, especially when VATS techniques are used. Observing the differential ventilation of the individual segments by clamping the segmental bronchus before (or after) full inflation can better delineate the intersegmental plane (Fig. 73-3). The segmental bronchus is then divided with a stapler or scalpel and closed in routine fashion. For suturing the bronchial stump, we prefer two over-and-over running 4-0 absorbable monofilament sutures after folding the membranous part inside the lumen of the bronchus and bringing the cartilaginous rings together according to the technique previously described by the Dutch surgeon Klinkenberg. Finally, the parenchyma between the involved and adjacent segments needs to be divided for which two techniques have been described: the open and stapled division.




Figure 73-3


A simple technique for determining the appropriate plane for parenchymal division is shown. After the segmental bronchus is clamped, the anesthetist is asked to gently inflate the lung while the surgeon observes the demarcation between the inflated and the deflated segment.





For the open technique, the intersegmental plane is teased apart by using a clamp to place traction on the stump of the transected segmental bronchus, whereas the rest of the lung is well ventilated. Sharp and blunt finger dissection may also help to open the intersegmental plane (Fig. 73-4). Cautery, harmonic scalpel, or small vascular clips are used to ensure hemostasis. Small air leaks can be oversewn with fine sutures. In addition, the raw surface of the adjacent segment can be covered with pleural or pericardial fat pad. Care has to be taken to avoid compression or kinking of the remaining bronchovascular structures which can result in a nonfunctional lobe thereby eliminating the benefit of segmentectomy versus lobectomy. The advantage of the open technique is that reexpansion of the adjacent parenchyma is maximal, but it carries a higher risk of prolonged air leaks.




Figure 73-4


For open division of the segmental parenchyma, traction is applied to the distal transected segmental bronchus, and the intersegmental plane is developed sharply or bluntly with finger dissection.





For the stapled technique, the virtual fissure is compressed and cut with the aid of a linear stapler. We prefer an endovascular linear cutting stapler. This technique results in better pneumostatic control in the remaining lung but it comes at the expense of volume loss as the visceral pleural layers are drawn together when closing the device. The remaining parenchyma is then somewhat trapped by the individual staplers, which blocks reexpansion of the lobe to its maximum volume (Fig. 73-5). The “extended” segmentectomy is accomplished by deploying the stapler lateral to the intersegmental plane so as to include the adjacent subsegments in the specimen.7


Dec 30, 2018 | Posted by in VASCULAR SURGERY | Comments Off on Segmentectomy for Primary Lung Cancer
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