Sublobar pulmonary resections encompass all pulmonary resections of less than an anatomic lobectomy. They are subdivided into two distinct categories, anatomic, otherwise known as segmentectomy versus nonanatomic, commonly referred to as a wedge resection. Segmental resections were originally considered for patients with limited inflammatory disease, such as aspergilloma, tuberculosis, and bronchiectasis, but the indications have expanded to include metastatic disease to the lung as well as primary lung cancer in patients with poor pulmonary reserve.

It is easy to recommend sublobar resections for diagnostic procedures and benign disease but it is a more complicated decision when dealing with malignant disease. For disease that is metastatic to the lung where preservation of pulmonary parenchyma is a guiding principle, segmentectomy or wedge resection is the procedure of choice if surgery is indicated and the anatomy is amenable to sublobar resection. There is no clear evidence that more radical resection results in better survival or lower recurrence, and frequently these patients require resection of multiple lesions usually dictating smaller individual resections.

The decision to proceed with a sublobar resection for primary lung cancer is complex, and continues to evolve. The predominant indication is for patients with poor pulmonary reserve, yet this concept is ill-defined and inconsistently applied. Traditional teaching has mandated that patients require a predicted postoperative FEV₁ >0.8 to 1.0 L/s to have sufficient pulmonary reserve to maintain adequate short- and long-term functional capacity. However, two factors have contributed to thinking differently about the traditional teaching. Improvements in operative technique, anesthesia, postoperative pain management, and respiratory care have allowed successful thoracotomy and pulmonary resection even in patients with major comorbidity and/or with patients with a low preoperative FEV1, even less than 0.5 L/s. Clearly these patients are at increased risk of postoperative pulmonary complications but it is unusual that these risks are prohibitive. These patients also have relative contraindications to radiation therapy or chemotherapy and may suffer similar or greater pulmonary complications or loss of function due to radiation when compared to surgery. In patients with major comorbidity a discrete intervention like a surgical procedure is often better tolerated than the less immediate, but insidious and progressive consequences of radiation.

The second factor changing the thinking regarding indications for surgery results from the recent experience with lung volume reduction surgery, which paradoxically often results in an increase in pulmonary function and exercise capacity when overinflated poorly functioning lung parenchyma is removed in selected emphysema patients. Patients with severe upper lobe-predominant emphysema, hyperinflation, and a tumor in the upper lobe, may actually be well served by a lobectomy or a lung reduction style of wedge resection, and actually have an improvement rather than a decrement in postoperative lung function.

The major factor that compels surgical consideration for lung cancer patients, even in those with major comorbidity, is that resection provides the only meaningful opportunity for cure. This is probably not an important factor if a patient’s anticipated life expectancy from his/her other disease(s) is less than 1 to 2 years, but for the majority of patients every effort should be made to try to offer surgical therapy with curative intent. Standard lobectomy should be possible in the majority of patients with nonpulmonary comorbidity.

The Lung Cancer Study Group in a classic study conducted a randomized trial that confirmed that lobectomy is the procedure of choice for patients with lung cancer, but sublobar resection and in particular segmentectomy are a reasonable compromise for those patients who are unable to tolerate a lobectomy. However, in the past few years several investigators have suggested that sublobar resections may have similar or equal outcomes to lobectomy in select patients. Lung cancer screening using low-dose spiral computed tomographic (CT) scanning has now been shown to reduce lung cancer deaths in high-risk patients (age >55 and smoking history >30 pack-years). As screening becomes more widely available, smaller lung cancers (<2 cm) are identified. It is likely that the incidence of sublobar resections of these early stage lung cancers is likely to increase. A number of thoracic surgeons already have challenged the standard dogma that lobectomy is mandatory for all lung cancer resections arguing that subcentimeter tumors may be adequately treated by wedge resection or segmentectomy, even in patients with adequate pulmonary reserve. More recently, several single-institution studies suggested that segmentectomy or extended wedge resections may be equivalent to lobectomy in appropriately selected stage IA lung cancer patients, but definitive evidence of oncologic equivalence awaits further follow-up. Currently, a National Cancer Institute-sponsored multicenter study (CALGB-140503) is underway comparing patient outcomes between lobectomy versus sublobar resections (wedge resection or segmentectomy) in small peripheral stage IA nonsmall-cell lung cancer. The study is powered such that results of this phase III randomized clinical trial will likely answer this important question.

Low-dose CT screening also has resulted in the identification of nodules with an alveolar filling appearance rather than a solid appearance, known as ground glass opacities (GGO). The appearance of GGOs on screening CT scans has led to a renewed appreciation of the subset of lung cancer known as bronchioloalveolar carcinoma (BAC), which in its pure form is a noninvasive subset of adenocarcinoma that has little potential for lymphatic and hematogenous metastases. Yet BAC may spread within the airway resulting in a late parenchymal metastasis appropriate for further surgical resection. GGO are frequently
BAC and may be best treated by sublobar resections since they have a low malignant potential by traditional criteria, yet may need additional pulmonary resections in the future due to the natural history of BAC. However, it is important to differentiate pure BAC from invasive adenocarcinoma with BAC features. The former may be treated by sublobar resection, but the presence of invasive carcinoma should indicate the need for a lobectomy if possible.

There are anatomic considerations that influence appropriateness of sublobar resections as well. Although exceptions always exist, generally segmentectomy and wedge resection are reserved for those patients with more peripheral and smaller tumors, a rough guideline being in the outer third of the lung parenchyma, and less than 3 cm in diameter, respectively. It is possible to consider limited resection for larger or more central tumors, but these will almost always require an anatomic segmentectomy in order to achieve adequate tumor margins. Another anatomic factor is the location of the tumor within the lung. A tumor that is close to or crosses an anatomic segment may require a bisegmentectomy or “cheating” into the adjacent segment with a staple line beyond the segmental boundary. Wedge resections are easiest (i.e., most successful) near acute lung edges, where it is possible to achieve adequate deep margins without encountering lung parenchyma that is too thick to staple. Therefore, peripheral tumors at the lung apex, lung base, or adjacent to a fissure are most amenable to an effective wedge resection.

Segmental resections are based on the principle of following the lymphatic drainage and bronchial branches of the segments resected. This provides a theoretical advantage over nonanatomic wedge resection in the treatment of primary lung cancer. However, segmental resections are also the least common type of pulmonary resection performed and are technically more challenging than lobectomy or pneumonectomy. This frequently results in wedge resections being performed as a default sublobar resection when parenchymal preservation is desired, due to inexperience with the indications for segmentectomy and lack of confidence in the technical components of segmentectomy.

Wedge resection of the lung is performed for a wide variety of indications, including lung biopsy for interstitial or infiltrative processes, excisional biopsy of a lung nodule, and definitive resection of a primary lung cancer or metastatic disease. With the current variety of standard and endoscopic staplers, wedge resection has become extremely easy and reliable. But, as a result, wedge resection is at risk of being overutilized, the technical simplicity being a seductive attraction to the surgeon with little thoracic surgical training or experience. Most of these surgeons have little or no experience with segmentectomy and so frequently will prefer a wedge resection procedure when a segmentectomy, or even a lobectomy, would be preferred for anatomic or oncologic reasons.

There are clear theoretical reasons explaining why anatomic segmentectomy may be superior to wedge resection for primary lung cancer. A segmental resection results in more reproducible deep parenchymal margins, since it extends the resection to the pulmonary hilum. Segmentectomy also incorporates the lymphatic drainage and interlobar lymph nodes and so may result in both more thorough resection as well as more accurate staging. Several studies have suggested decreased rates of local recurrence with segmentectomy but no well-designed study comparing segmentectomy to wedge resection has been performed. However, it is quite possible that the appearance of better cancer outcomes after segmentectomy may be substantially biased because of inappropriate or inadequate wedge resections being performed by less-experienced surgeons. It is reasonable to postulate that outcomes between wedge resection and segmentectomy for primary lung cancer may be similar as long as three principles are adhered to: (1) adequate sampling of N1 and N2 lymph nodes to exclude stage II and stage III disease; (2) at least a 2-cm parenchymal margin around the tumor; (3) restriction of lung cancer surgery to surgeons trained in thoracic surgical oncology who perform a high volume of pulmonary resections in order to have the experience and expertise to select patients who truly require sublobar resection, or who may benefit from segmentectomy rather than wedge resection.