Segmental resection, or segmentectomy, describes a technique of excising lung tissue that proceeds along anatomic planes based on the bronchovascular anatomy. It involves division and closure of the segmental bronchus along with the corresponding blood supply, followed by dissection and removal of the lung along the intersegmental planes. A wedge resection, sometimes referred to as a segmentectomy owing to its sublobar status, is not an anatomic resection and should not be confused with a segmentectomy. This is an important distinction because this confusion likely has tainted the data used to recommend segmental resection as an adequate cancer operation. In the setting of node-negative disease (N₀), a segmentectomy is likely an adequate cancer operation, whereas a wedge resection would be suboptimal.

HISTORY

Although early work by Ewart in the late 1800s characterized the bronchial and vascular anatomy of the lung,¹ the term bronchopulmonary segment was coined by Kramer and Glass in 1932.² A few years later, in 1939, the technique of a segmental resection was described by Churchill and Belsey.³ Their pioneering surgeries were performed for bronchiectasis and tuberculosis, however, not cancer. Shortly thereafter, surgeons began performing limited resections for bronchogenic carcinoma. Until 1973, there were no large group studies comparing the efficacy of segmental resection versus lobectomy for non-small cell lung cancer (NSCLC).⁴ Since then, limited resection for cancer has continued to be an area of controversy and has been plagued by conflicting studies comparing the technique with standard lobectomy and pneumonectomy. Segmentectomy consequently is used in limited situations in the clinical realm, and lobectomy and pneumonectomy continue to be favored as the curative procedures of choice.

INDICATIONS

Although there are no absolute indications for performing segmentectomy, the technique has been used for a myriad of lung disorders. As mentioned earlier, the operation was performed initially for bronchiectasis and tuberculosis. Other conditions for which the procedure has been used include aspergilloma, pulmonary sequestration, other pulmonary infections, pulmonary abscesses, benign tumors of the lung (e.g., hamartomas, papillomas, etc.), and metastatic lesions involving the lung. In the modern era of pulmonary surgery, the advent of antibiotic therapy led to a decrease in segmentectomies performed for infectious lung processes and an increase in their use for primary malignancies of the lung.⁵

Limited resections (segmentectomy and wedge resection) are also performed as curative resections for cancers in selected patients, including two major groups, as described by Jensik.⁶ These are patients with physical contraindications and patients with limited disease who otherwise would tolerate a lobectomy. The former group consists primarily of patients with limited pulmonary reserve and is not an area of controversy. Segmental resections for patients who would tolerate a larger resection remains an area of debate, likely a result of the Lung Cancer Study Group trial published in 1995.⁷ The results of this trial showed a threefold increase in local recurrence rate and a 50% increase in number of patients who died with cancer when they compared the limited-resection arm with the lobectomy arm for NSCLC tumors of less than 3 cm in diameter. This study, however, included nonanatomic wedge resection and anatomic segmentectomy in the same group.

An earlier retrospective study⁸ compared anatomic segmental resection (excluding wedge resections) with lobectomy. This study found no significant difference in survival for tumors less than 3 cm in diameter. Lobectomy was shown to correlate with better survival in patients with tumors larger than 3 cm, but the majority (59%) of patients who died within 5 years of surgery in both the lobectomy and segmentectomy groups died of causes other than local or distant recurrences. The study did, however, report a 4.6-fold increase in local/regional recurrence (22.7% versus 4.9%) in the segmentectomy group versus the lobectomy group.

A number of single and multi-institution retrospective and prospective studies, primarily from Japan, have put forth data in favor of segmental resection for small, peripheral tumors.^9–11 In these studies, comparable survival results were seen in patients with T₁N₀M₀ tumors of less than 2 cm between "extended" segmental resection and standard lobectomy groups (extended meaning the resection line is located on the segment adjacent to the resected segment in order to obtain sufficient margin). Others¹² also have reported the absence of statistically significant differences in overall or lung cancer-specific 5-year survival between lobectomy and segmental resection groups for stage I tumors of less than 1 cm. However, a statistically significant difference was observed when they compared both lobectomy and segmentectomy with wedge resection for similar tumors (overall survival of 71%, 57%, and 27% for lobectomy, segmentectomy, and wedge excision, respectively). This study also confirmed a potential role for anatomic segmental resection of small tumors in patients who otherwise could tolerate a standard lobectomy.

PREOPERATIVE ASSESSMENT

Preoperative workup and evaluation for thoracic surgery is discussed elsewhere in this text, and the same principles apply for segmentectomy (see Chap. 4). The patient is evaluated from a medical perspective to ensure that he or she is a safe candidate for pulmonary resection. The patient is also evaluated from an oncologic perspective to ensure, as much as is humanly possible, the presence of stage I disease. Our practice is to perform a CT scan of the chest and upper abdomen, a PET scan to rule out extrathoracic disease, and an MRI to rule out brain metastasis. Although radiographic staging can rule out N₂ disease with a moderate-to-high degree of accuracy, it still does not match mediastinoscopy. As a consequence, we perform mediastinoscopy in most of our patients. To avoid the low but real incidence of false-negative readings, the main limitation of frozen-section pathology, we prefer to perform the mediastinoscopy as an outpatient procedure. We perform a bronchoscopy at the same time to detect the presence of endobronchial disease that may have eluded the radiographic workup.

While there is no one correct algorithm for preoperative pulmonary testing, many test parameters have been shown to correlate with increased operative morbidity¹³: stair climbing less than three flights, maximum voluntary ventilation (MVV) less than 50 L/min, forced expiratory volume in 1 second (FEV₁) less than 50% of the forced vital capacity (FVC), and diffusing capacity of the lung for carbon monoxide (DLCO) less than 50%. In addition, a limited pulmonary resection (wedge or segmentectomy) can be tolerated with a preoperative FEV₁ as low as 0.6 L, with a forced expiratory flow (FEF_25-75%) as low as 0.6 L, and with a maximum voluntary ventilation as low as 35%.¹³ Recent reports have suggested that patients with an FEV₁ and DLCO of greater than 60% predicted require no further testing, whereas patients with lower values should undergo radionuclide scanning.¹⁴

SURGICAL TECHNIQUE

We favor epidural pain control for all thoracotomy patients. In patients for whom a limited resection is contemplated because of poor pulmonary function, the nonsedating pain control afforded by epidural analgesia is critical. With rare exceptions, we perform mediastinoscopy for staging NSCLC patients as we continue to obtain pathologic staging that contradicts the CT/PET radiographic staging. We generally perform the mediastinoscopy as a separate outpatient procedure to avoid the small but real false-negative rate associated with frozen-section pathology. The procedure, however, can be performed concomitantly with the thoracotomy. In all patients, a bronchoscopy is performed to visualize the airway for evidence of occult endobronchial lesions or other pathology. A double-lumen endotracheal tube is used for selective ventilation.

The patient is placed in the lateral decubitus position, and the chest is entered through the fifth interspace, although the fourth interspace sometimes may appear more appropriate for upper lobe lesions. Our standard incision involves division of the midportion of the latissimus and mobilization/retraction of the serratus. On entrance to the chest cavity, a full examination of the lung is conducted, and the remainder of the hemithorax is inspected and palpated carefully to rule out other pathology. If a preoperative diagnosis has been established, the surgeon can commence with the resection. If the lesion is located peripherally and clearly within a segment, a wedge resection can be performed to establish a diagnosis. If the lesion is central or if performing a wedge resection will preclude subsequently performing a segmentectomy, the surgeon has the option of performing a needle biopsy or proceeding presumptively with the segmental resection. It is also important at this time to determine whether the lesion can be excised adequately with appropriate margins by segmentectomy alone or if an extended segmentectomy or lobectomy needs to be performed.

Once it has been determined that a segmental resection is feasible and appropriate, the first step is usually to identify the appropriate arterial branches (Fig. 65-1). Many surgeons will operate without proximal arterial control. It is our usual practice to encircle the main pulmonary artery with a vascular tape for proximal control. The arterial branches are divided in the usual manner, and when the branches that are approached from the fissure are divided, the underlying segmental bronchus is exposed. Traction on the segment itself can aid in identifying the appropriate segmental bronchus and arteries. If the segmental resection is being performed for cancer, it is prudent to send hilar and intersegmental lymph nodes to pathology for frozen-section analysis. The presence of metastatic disease in any of these N₁ lymph nodes likely represents an indication to proceed with a lobectomy that encompasses the site of the pathologic nodes rather than limiting the anatomic resection to the side of the affected nodes. The segmental vein travels closer to the periphery of the segment and may be easier to identify after dissection of the intersegmental plane has commenced. Again, traction on the divided segment usually will permit identification of the appropriate segmental veins as they drain into parental superior and inferior venous trunks.

Determining the appropriate plane for parenchymal division can be challenging. The easiest technique is to clamp the segmental bronchus and to have the anesthesia team gently inflate the lung (Fig. 65-2). The first several puffs likely will delineate the parenchyma supplied by that bronchus. If the patient naturally has a large degree of intersegmental cross-ventilation, or if the patient suffers from chronic obstructive pulmonary disease, the diseased segment may fill through collateral "pores of Kohn."⁵ In such cases, 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.¹⁵

After identifying the intersegmental plane, the segmental bronchus is either divided using a stapler or divided sharply and closed with interrupted absorbable sutures. There are two ways to divide the segmental parenchyma—open and staple division. The advantage of open division is that there is likely greater preservation of lung volume, but this technique results in a greater number of air leaks. Staple division results in a pneumostatic division of the lung but comes at the expense of volume loss as the visceral pleural layers are drawn together during the act of stapling (Fig. 65-3).

Open division is accomplished by applying traction to the distal transected segmental bronchus and developing the intersegmental plane sharply or with blunt finger dissection (Fig. 65-4). With this technique, it may be necessary to ligate or clip small vein branches and bronchi in the intersegmental plane. Care must be taken to preserve the intersegmental vein. Once the segment is removed, adequate hemostasis must be achieved, and any small air leaks can be oversewn with fine absorbable sutures. In addition, the exposed surface of the adjacent segment can be covered with pleural flaps or sutured to an adjacent raw surface. This practice, however, can result in kinking of the remaining bronchial architecture, thereby eliminating the benefit of performing segmentectomy versus lobectomy.

Stapled division of the segment, our preferred technique, is accomplished by following the demarcation between inflated and atelectatic lung, as described earlier, during the inflation or deflation maneuver with the segmental bronchus clamped. The appropriate segmental veins can be incorporated in the staple line and may obviate the need for separate identification and ligation of the segmental pulmonary veins. The "extended" segmentectomy is accomplished by deploying the stapler lateral to the intersegmental plane so as to include the adjacent subsegments in the specimen.⁹

When segmentectomy is performed for a suspected primary malignancy, peribronchial and intersegmental lymph nodes are removed with the specimen. In addition, mediastinal lymph node dissection must be performed. It is our practice to freeze these lymph nodes and consider escalating to a lobectomy if these nodes contain metastatic disease.

While any segments can be removed, certain operations are performed more commonly, especially for T₁N₀ NSCLC operations. These include taking or sparing the superior segment for lower lobe cancers and taking or sparing the lingular segment for left upper lobe cancers. A brief description of each segmental resection follows.

A few technical points are common to all segmental resections. First, never compromise the superior or inferior venous trunk when dividing the segmental vein. This mistake can lead to venous thrombosis and potentially disastrous results that may present in an insidious manner during the postoperative period. Second, consider instituting proximal pulmonary arterial control, especially when extensive dissection in the fissure is anticipated. Having this control can convert a potentially lethal problem into an inconvenience. Intraoperative bronchoscopy also can be very helpful if there is any confusion regarding the segmental anatomy or if there is concern about potential compromise to the adjacent segmental bronchial orifice. A pediatric bronchoscope will fit through the lumen of a double-lumen endotracheal tube. Not only will the scope reveal an endobronchial view, but also the light will transilluminate the airway, and it can be visualized from the operative field.

Right Upper Lobe

The apical segment dissection is begun by incising the mediastinal pleura. The apical branch of the anterior arterial trunk is identified and divided. The apical segmental bronchus then is approached posteriorly and isolated after ligating the bronchial artery branches. For right upper lobe segmentectomy, the vein usually is encompassed in the staple line.

In performing a posterior segmentectomy, the major fissure is opened posteriorly, and the posterior segmental artery is identified and ligated. Alternatively, the artery branch is ligated after dissection and transection of the segmental bronchus, which can be tracked posteriorly along the right upper lobe bronchus.

The anterior segment is approached from the medial aspect, beginning with incision of the mediastinal pleura. The anterior segmental artery is identified as it branches from the anterior arterial trunk. The anterior segmental vein likewise is identified and ligated, taking care not to compromise other segmental tributaries to the superior pulmonary vein. The horizontal fissure is completed, the anterior segmental bronchus is divided, and the segment is excised.

Superior Segment, Right Lower Lobe

If the major fissure is well developed, the pulmonary artery can be approached directly in the fissure. If the fissure is incomplete, it must be first developed to expose the artery. The pleura is opened posteriorly, at the bifurcation of the right upper lobe bronchus and the bronchus intermedius, and continued anteriorly to identify the recurrent artery to the posterior segment of the upper lobe and the superior segmental artery to the lower lobe. With these bifurcations visualized, the posterior portion of the major fissure can be developed. A stapler can be used to divide the parenchyma, taking care to exclude the arteries and bronchi from the jaws of the stapler. Sometimes it is helpful to place a 0.25-inch Penrose drain through the "window" that has been created and feed the lower jaw of the stapler into the drain. The drain then can be used to guide the stapler through the window without risk of falsely passing the stapler and injuring or dividing a vessel or bronchus. The posterior fissure can be a difficult spot to manipulate with a stapler, and passing the stapler through the future chest tube site may afford a more benevolent angle of attack.

Once the posterior portion of the major fissure is opened, the artery can be isolated and divided. This will provide exposure to the bronchus, which runs deep to the artery. The superior segmental vein usually can be identified posteriorly as a separate tributary running into the inferior vein. Again, care must be taken not to compromise the remainder of the vein.

Left Upper Lobe

Proximal control of the pulmonary artery facilitates the practice of left upper lobe segmentectomy. With control and visualization of the pulmonary artery, the oblique fissure is completed. The segmental arteries then are exposed, and the appropriate branches are divided. Once the arterial branch is divided, the segmental bronchus is exposed and similarly divided. The parenchymal completion of the segmentectomy is then completed as earlier.

Lingula

As with most segmental resections, the ease of dissection is a function of the completeness of the fissure. If the fissure is complete, the artery can be identified, and the branches can be identified and isolated. If the fissure is not complete, then it must be developed, and this is best accomplished by tracing the pulmonary artery into the fissure. It is our practice to obtain proximal control on the artery before initiating this dissection. Once proximal control is secure, the parenchyma overlying the artery within the fissure is divided. Commonly, a plane can be developed between the lobes using sharp dissection or a very low setting on the electrocautery that will not result in significant air leaks. If raw parenchyma is encountered, as the fissure is developed, we will complete the fissure with a stapling device. The lingular arteries may arise separately as a common trunk from the ongoing pulmonary artery. The lingular bronchus will be found under the divided arteries (Fig. 65-5). Care must be taken to avoid compromising the superior divisional bronchus to the upper lobe when dividing the lingular bronchus. The lung is retracted posteriorly, and the hilar pleura is incised to expose the superior pulmonary vein. The lingular branch then is identified and divided. Finally, the parenchyma is divided as described for other segments.

Lingula-Sparing Left Upper Lobectomy

This procedure is identical to the lingulectomy, but the superior division left upper lobe structures are divided, and the lingula is spared.

POSTOPERATIVE CARE

Before closure, we typically use a single 28F chest tube directed posteriorly and apically to drain the pleural space. We use a rongeur to cut extra holes in the tube, taking care to put the most proximal hole through the radiopaque line and to leave a generous margin between that hole and the chest wall to avoid entraining air into the chest wall. A more traditional drainage scheme is to place two straight tubes, anteriorly and posteriorly, to the apex. There are numerous practices for chest tube management. Our practice is to place the tube on suction immediately after extubation, to evacuate air, and then to leave the tube on waterseal unless there is an increasing pneumothorax or subcutaneous emphysema develops. The focus of postoperative care is pulmonary toilet and achieving the appropriate level of analgesia to accomplish this goal.

COMPLICATIONS

The Lung Cancer Study Group (1995) found no significant difference in postoperative morbidity or mortality between the lobectomy and segmentectomy groups. The most common morbidities included persistent air leak (10%) and atelectasis (16%).¹⁵ Use of stapling devices has decreased the incidence of persistent air leaks. A rare but reported complication is the development of a pseudotumor after stapled segmentectomy as a result of presumed vascular insult in the remaining segment of the lobe.¹⁶

SUMMARY

Segmental resection has been part of the thoracic surgeon's armamentarium for almost 65 years. In the last quarter of a century, however, use of this procedure has become less common as a consequence of the decreased incidence of surgery for infection. The recent resurgence of interest in segmental resection for lung cancer can be attributed to the apparent adequacy of this operation for T₁N₀ cancers. Early published results for segmental resections for lung cancer likely were tainted by the inclusion of nonanatomic wedge resections with the results for anatomic segmental resections. Segmental resections can be technically challenging, but they do offer the advantage of preserving functional lung parenchyma and may represent the most appropriate option for patients with compromised pulmonary function.

EDITOR'S COMMENT

Segmentectomy is quickly becoming "a lost art." First used for lung cancer by Dr. Richard Overholt of Boston, MA, this approach received wide acceptance after a description of the success by Jensik and Faber. In high-risk patients who cannot tolerate a lobectomy, anatomic segmentectomy should be considered. The key to success is to dissect the segment along the intersegmental veins after the segmental artery and bronchus have been divided. Although it is still not clear if these patients do better long term than those undergoing wedge resection, there is a bias that segmentectomy with anatomic dissection and lymph node dissection is a better cancer operation.

–MJK

REFERENCES