Pulmonary Vasculature & Bronchopulmonary Segments
Surgical anatomy of the hilum — the knowledge that determines safe vessel control in every lung resection.
Pulmonary artery vs. pulmonary veins
The pulmonary circulation carries deoxygenated blood from the right heart to the lungs and returns oxygenated blood to the left heart. The two vessel types differ fundamentally in structure, course, and surgical relevance.
| Feature | Pulmonary artery | Pulmonary veins |
|---|---|---|
| Blood carried | Deoxygenated — right ventricle to lung | Oxygenated — lung to left atrium |
| Course of segmental branches | Alongside respective bronchi | Run in interlobular septae (intersegmental planes) |
| Wall structure | Lack muscular and elastic elements; derive strength from intima — fragile and prone to tears | Relatively thick-walled compared to arteries |
| Valves | Present | Absent |
| Surgical significance | First structure divided in anatomical resection; intrapericardial control may be required | Most anterior and inferior hilar structure; intersegmental course defines segmental planes |
The pulmonary artery wall is fragile — it lacks the muscular and elastic elements of systemic arteries and derives its strength primarily from the intimal layer. Tearing occurs easily during dissection in fibrotic or inflamed hila. Proximal vascular control — intrapericardial if necessary — must be established before proceeding with difficult hilar dissection.
Pulmonary artery
Intrapericardial course
The main pulmonary artery (pulmonary trunk) arises from the right ventricular outflow tract. The aorta and pulmonary artery are enclosed in a sleeve of visceral pericardium (the arterial mesocardium). This sleeve is separated from the venous mesocardium — which covers the pulmonary veins, SVC, and IVC — by the transverse sinus.
Below the aortic arch, the main pulmonary artery bifurcates into right and left main pulmonary arteries at the level of the carina.
Right pulmonary artery (RPA)
The RPA has a longer, more horizontal course than the left. It lies within the pericardium for more than three-quarters of its length, running horizontally to the right behind the ascending aorta and SVC.
- Behind the ascending aorta — RPA forms the superior border of the transverse sinus
- Behind the SVC — RPA forms the superior border of the post-caval recess of Allison, bounded inferiorly by the superior pulmonary vein
- Covered by serous pericardium over its anterior three-quarters; posterior surface is applied directly to fibrous pericardium — serous pericardium must be divided to access the full circumference
- Accessed by retracting the aorta medially and the SVC laterally
Left pulmonary artery (LPA)
The LPA is more accessible intrapericardially than the right. It passes under the aortic arch to exit the pericardial sac and has a relatively short intrapericardial course.
- Forms the superior border of the left pulmonary recess, bounded inferiorly by the left superior pulmonary vein and laterally by fibrous pericardium
- Between LPA and superior pulmonary vein lies the ligament of the left vena cava (vestigial fold of Marshall) — dividing this fold improves intrapericardial access to the LPA
- Covered by serous pericardium over its anterior half only
Intrapericardial control of the pulmonary artery is required when extrapericardial dissection is unsafe — in destroyed lung, post-TB fibrosis, calcified nodes encasing the hilum, or completion pneumonectomy. The RPA is approached by retracting the aorta and SVC; the LPA by dividing the fold of Marshall. Establishing proximal control before entering the hilum is the key safety manoeuvre.
Extrapericardial course — right side
As it leaves the pericardium, the RPA lies anterior and inferior to the right mainstem bronchus. Its first and largest branch is the truncus anterior, given off before entering the hilum. The RPA then continues as the interlobar pulmonary artery (pars intralobares), running inferiorly between the bronchus intermedius posteriorly and the superior pulmonary vein anteriorly.
Segmental arteries — right: Truncus anterior supplies the apical and anterior segments of the upper lobe. The posterior segment of the RUL is supplied by the posterior ascending (recurrent) artery — a thin branch off the lateral wall of the interlobar artery. At the same level, the middle lobe artery arises anteromedially, and the superior segment artery of the lower lobe arises posteriorly. This trifurcation lies at the junction of the horizontal and oblique fissures — a key surgical landmark.
Extrapericardial course — left side
The LPA exits the pericardium below the aortic arch at the ligamentum arteriosum. It has a relatively long extrapericardial course before giving its first branch, then continues as the common basal trunk.
Segmental arteries — left: Anatomical variation on the left is far more common than on the right. The number of arterial branches to the LUL varies from 2 to 7. Most commonly, the apicoposterior and anterior segments are supplied by the apicoanterior trunk. The lingula is supplied by a separate branch. The superior segment of the LLL arises next, followed by the basal artery.
Pulmonary veins
There are typically four pulmonary veins — right and left superior, right and left inferior — carrying oxygenated blood from the lungs to the left atrium. The pulmonary veins lie below and anterior to the pulmonary arteries in the middle mediastinum.
- Distal segments are intrapericardial
- Inferior pulmonary vein ostia are more posterior and medial than those of the superior veins
- Left pulmonary vein ostia are higher in the left atrium than those on the right
- In both hilae: superior pulmonary vein is the most anterior structure; inferior pulmonary vein is the most inferior structure
Pulmonary vein branches run within interlobular septae and do not parallel the segmental arteries or bronchi. They run in intersegmental planes — and are therefore the intraoperative landmarks for identifying and developing the plane between bronchopulmonary segments during segmentectomy.
Bronchopulmonary segments
A bronchopulmonary segment (BPS) is an anatomical unit of lung supplied by a specific tertiary (segmental) bronchus with an accompanying segmental artery. The general pattern is 10 segments on the right and 8 segments on the left.
The left lung has 8 functional segments in the surgical convention: LB1 and LB2 are fused as the apicoposterior segment (LB1/2), and LB7 and LB8 are fused as the anteromedial basal segment (LB7/8). This reflects the anatomical reality during resection planning. Some anatomical texts describe 9–10 left segments by counting the fused segments separately.
| Right lung (10 segments) | Left lung (8 segments) |
|---|---|
| Upper lobe | Upper lobe |
| RB1 — Apical | LB1/2 — Apicoposterior (fused) |
| RB2 — Posterior | LB3 — Anterior |
| RB3 — Anterior | |
| Middle lobe | Lingula |
| RB4 — Lateral | LB4 — Superior lingular |
| RB5 — Medial | LB5 — Inferior lingular |
| Lower lobe | Lower lobe |
| RB6 — Superior | LB6 — Superior |
| RB7 — Medial basal (cardiac) | LB7/8 — Anteromedial basal (fused) |
| RB8 — Anterior basal | LB9 — Lateral basal |
| RB9 — Lateral basal | LB10 — Posterior basal |
| RB10 — Posterior basal |
Each BPS is supplied by a segmental bronchus and artery with no communication between adjacent segments. This discrete anatomy permits surgical removal of individual segments (segmentectomy) without damage to neighbours. Intersegmental veins mark the surgical plane. Segmentectomy preserves pulmonary reserve — critical in patients with compromised lung function and increasingly preferred over lobectomy for small peripheral tumours (<2 cm).
All clinical content should be verified against current guidelines before clinical application. This resource is intended for revision and educational purposes only.
Standard textbooks
- Shields TW, LoCicero J, Reed CE, Feins RH. General Thoracic Surgery. 7th ed. Lippincott Williams & Wilkins.
- Sellke FW, del Nido PJ, Swanson SJ. Sabiston & Spencer Surgery of the Chest. 9th ed. Elsevier.
- Pearson FG, et al. Thoracic Surgery. 3rd ed. Churchill Livingstone.