Surgical Anatomy of the Lungs

Abstract

Anatomical lung resections are specialized procedures that require a good knowledge of anatomy and high surgical experience. Individual isolation and dissection of hilar structures, including pulmonary arteries, pulmonary veins, and bronchus, are the basic steps of anatomic lung resection. Today, lobectomy is still the gold standard treatment method in many lung pathologies, especially in early-stage lung cancer. In-depth knowledge of anatomy, including variations, is required to perform this surgical procedure safely and successfully, which has a relatively high risk of intraoperative complications. Technological developments and the spread of minimally invasive surgery paved the way for the recording of procedures and their use for educational purposes and that ushered in a new era in surgical education. These developments in video-assisted surgery, which is an excellent advantage for patient comfort and education, have made the digital exploration of the surgeon impossible and increased the importance of theoretical anatomy knowledge even more. This chapter will discuss the lobar distribution of the lung, tracheobronchial airway, vascular structures, and their variations.

1. Introduction

Historically, the first lung resections were based on mass ligation of the hilum [1, 2, 3]. With the development of anesthesia techniques and increasing surgical experience, anatomical resections of the lung are performed with the isolation and transection of artery, vein, and bronchial structures separately. This makes the hilar anatomy of the lung and its possible variations important. In this chapter, it is planned to discuss the anatomy of the lung from the perspective of the thoracic surgeon, accompanied by intraoperative figures (Figures 1–3).

Figure 1.

Tracheobronchial anatomy (Boyden’s nomenclature). Right side: RB1: Apical bronchus, RB2: Anterior bronchus, RB3: Posterior bronchus, RB4: Lateral bronchus, RB5: Medial bronchus, RB6: Superior bronchus, RB7: Medial basal bronchus, RB8: Anterior basal bronchus, RB9: Lateral basal bronchus, and RB10: Posterior basal bronchus. Left side: LB1: Apical bronchus, LB2: Posterior bronchus (LB1 + LB2 forms apicoposterior bronchus), LB3: Anterior bronchus, LB4: Superior lingular bronchus, LB5: Inferior lingular bronchus, LB6: Superior bronchus, LB7 + LB8: Anterior basal bronchus, LB9: Lateral basal bronchus, and LB10: Posterior basal bronchus.

Figure 2.

After the transection of the left superior pulmonary vein, the pulmonary artery and its first branch are clearly observed. Asterisk indicates the left main pulmonary artery. The arrow indicates the apicoposterior segment artery. “B” indicates the left main bronchus. Triangles indicate proximal and distal parts of the upper lobe vein stump.

Figure 3.

After the transection of the right superior pulmonary vein, the upper lobe pulmonary artery and interlobar artery are clearly observed. Asterisks indicate proximal and distal parts of the upper lobe vein stump. SVC: superior vena cava.

2. Tracheobronchial tree

The tracheobronchial tree transmits air from the upper respiratory tract to the lung parenchyma. The right and left bronchial systems contain some differences.

The left main bronchus is longer than the right main bronchus. The left upper lobe bronchus arises from the anterosuperior of the main bronchus and divides into two, forming the upper and lower bronchial divisions. The upper division divides into two to form the apical-posterior and anterior segmental bronchi. The lower division, also known as the lingular bronchus, divides into the superior and inferior lingular segments. The lower lobe bronchus is relatively short due to the branching of the superior segment bronchus. There may be differences in the nomenclature of the basal segments on the left side. The anterior and medial basal segments of the left lower lobe branch from the same root. For this reason, some authors state that there are four basal segments in the left lower lobe (Figures 4–6) [4, 5, 6, 7].

Figure 4.

The left upper lobe tri-segment vein (V1) was dissected and retracted with a silicone vessel loop. A: left main pulmonary artery. V2: lingular vein. Arrow indicates the left main bronchus.

Figure 5.

The variation of the middle lobe vein is observed in a case who underwent a middle lobectomy. The middle lobe is drained by two vein branches that drain into the superior (RML-1) and inferior (RML-2) pulmonary veins. Arrow indicates transected middle lobe bronchus. Asterisk indicates transected RML-1.

Figure 6.

View of the left hilum after transection of the superior pulmonary vein. PA: pulmonary artery. Asterisk indicates the apicoposterior artery. B: left main bronchus. The lines indicate the bifurcations of the pulmonary artery and bronchus.

Unlike the left upper lobe bronchus, the right upper lobe segment bronchi branch separately as apical, posterior, and anterior. Middle lobe bronchus originates from the lateral wall of the intermediate bronchus and bifurcates into medial and lateral segment bronchi. After the superior segment bronchus is arise, a total of five basal segment bronchi branch separately.

3. Pulmonary artery

3.1 Left pulmonary artery

After originating from the heart, the pulmonary artery courses in the posterior and superior direction and divides into the left and right main pulmonary arteries below the aortic arch. The left pulmonary artery is located above and slightly anterior to the left main bronchus. It curves behind the upper lobe bronchus and enters the interlobar fissure. The first branch is usually the apicoposterior segment artery. The anterior segment artery usually arises in the interlobar fissure. Although it is rare, the apical, posterior, and anterior segment arteries can be branched separately. There are two common variations in the anterior artery. First, the anterior segment artery branches close to the hilum as the first branch of the pulmonary artery. The second variation is that it arises as a branch of the lingula artery within the interlobar fissure. The lingula segment artery usually branches at the level of the lower lobe superior artery. Basal segment arteries are localized parallel to the corresponding segmental bronchi (Figures 7–9).

Figure 7.

The anterior segment artery (arrow) seen after the transection of the apicoposterior artery (triangle) was dissected and retracted with a silicone vessel loop. Asterisk indicates the left main pulmonary artery.

Figure 8.

View of the left hilum after transection of the upper lobe vein and apicoposterior artery. Arrow indicates the stump of the apicoposterior artery. B1: upper lobe tri-segment bronchus. B2: lingular bronchus.

Figure 9.

The placement of the left pulmonary artery and its branches in the interlobar fissure. PA: pulmonary artery. L: lingular artery. 1 + 2: lower lobe superior segment arteries. 3: basal segment artery.

It should be noted that variations of the left upper lobe artery are very common, and the left upper lobe artery can give 2–7 branches, therefore the surgeon should always be alert for possible variations [8, 9].

3.2 Right pulmonary artery

The right pulmonary artery lies anterior and posterior to the upper lobe bronchus and gives a single root branch just before entering the interlobar fissure. This branch divides into the apical and anterior segment arteries. These branches supply most of the upper lobe. The posterior ascending artery feeding the posterior segment arises deep within the interlobar fissure (Figure 10).

Figure 10.

The appearance of the right hilum after transection of the middle lobe vein. A: interlobar pulmonary artery. V: upper lobe vein. B: bronchus intermedius. The arrow indicates the stump of the middle lobe vein. Asterisk indicates the middle lobe bronchus. The triangle indicates the lower lobe bronchus.

Variations of the right upper lobe artery are common. Apical and anterior branches may arise separately. The posterior ascending artery may arise from the middle lobe artery or the lower lobe superior segment artery. In 10% of the patients, the posterior ascending artery may be absent.

The middle lobe artery arises from the junction of the horizontal and oblique fissures and divides into two branches, medial and lateral. Sometimes a third accessory middle lobe branch can be seen.

The superior segment artery arises at the level of the middle lobe artery and divides into two branches. These branches may arise separately in some cases. In total, four basal segment arteries arise close to the lung parenchyma [8, 9, 10].

4. Pulmonary vein

4.1 Left pulmonary vein

The left pulmonary vein is the most anterior structure of the left lung hilum. The names of the segment veins of the upper lobe are similar to the names of the bronchi, as apicoposterior, anterior, and ligula.

The inferior pulmonary vein lies inferior and posterior to the superior pulmonary vein. It is located between the pleural folds, superior to the pulmonary ligament. It is best seen posteriorly. It consists of lower lobe superior and basal segment veins [8, 9, 11].

4.2 Right pulmonary vein

The right superior pulmonary vein is located anterior and slightly inferior to the right main pulmonary artery. It consists of the apical anterior, posterior, and middle lobe veins, from top to bottom, respectively. Cases where the middle lobe vein drains only into the inferior pulmonary vein or into both the superior and inferior pulmonary veins have been reported.

The inferior pulmonary vein is located below and posterior to the superior pulmonary vein, and drains the entire lower lobe. On the left, it has two main branches: the lower lobe superior segment vein and the basal veins. It is best seen posteriorly with the lung retracted anteriorly.

5. Surgical anatomy of the pulmonary hilum

The surgeon must know the location of the anatomical structures in the pulmonary hilus and their proximity to each other in order to perform safe dissection.

The unsymmetrical structure and location of the heart in the sagittal plane have created some differences between the right and left pulmonary hiluses in terms of anatomical neighborhoods.

In this section, it is planned to discuss the locations of the anatomical structures in the right and left pulmonary hilum from a surgical perspective.

5.1 Left hilum

The uppermost structure in the left lung hilum is the main pulmonary artery. The main pulmonary artery lies slightly above the main bronchus and curves behind the upper lobe bronchus to enter the interlobar fissure. After transection of the superior pulmonary vein, the main bronchus and the bifurcation of the lobe bronchi can be seen.

It should be kept in mind that the esophagus located medially and posteriorly may be injured during the dissection of the left main bronchus, especially in cases with severe adhesions between the mediastinal structures.

The inferior pulmonary vein is located superior to the pulmonary ligament, between the pleural folds. On the left side, the distance of the inferior pulmonary vein outside the pericardium is usually very short. This may lead to the unintended opening of the pericardium during dissection.

In some cases, the upper and lower pulmonary veins merge outside the pericardium and enter the pericardium as a single root [12, 13].

5.2 Right hilum

The most cephalic structure in the right hilum is the main bronchus. The main pulmonary artery is located anterior and inferior to the bronchus, so when the anterior approach is preferred, transection of the arterial branches leading to the upper lobe is required for visualization of the upper lobe bronchus.

After the main pulmonary artery gives apical and anterior branches, the posterior segment artery branches within the interlobar fissure.

However, this pulmonary artery branch, named posterior ascending artery, is not observed in the interlobar fissure in approximately 10% of the cases [14].

The middle lobe artery arises proximal to the lower lobe superior segment artery. Unlike the left lung, vein branches belonging to the posterior segment can be seen in the interlobar fissure, so this should be kept in mind when performing arterial dissection. After the posterior segment vein branches from the superior pulmonary vein, it moves posteriorly and enters the interlobar fissure. Therefore, care should be taken not to injure the posterior segment vein during the dissection or encircling of the superior pulmonary vein while performing the right upper lobectomy.

Conflict of interest

The author declares that he has no competing interests related to this chapter.