Left Pulmonary Veins

The left pulmonary veins are the vessels that return oxygenated blood from the left lung to the left atrium. In the usual arrangement, there are two major left pulmonary veins: the left superior pulmonary vein and the left inferior pulmonary vein.

These veins are part of the pulmonary circulation. Unlike most systemic veins, they carry blood with a high oxygen content because they receive blood that has passed through the pulmonary capillary beds surrounding the alveoli.

The left pulmonary veins form from progressively larger intrapulmonary veins, pass through the root of the left lung, and enter the posterior aspect of the left atrium. Their anatomy is especially important in cardiac imaging, thoracic surgery, pulmonary resection, and catheter ablation procedures for atrial fibrillation.

Number

Most individuals have two major pulmonary veins from the left lung.

• Left superior pulmonary vein
• Left inferior pulmonary vein

Anatomical variation is common, and tributaries may unite differently or occasionally form a common venous trunk before entering the left atrium.

Location

The left pulmonary veins extend from the hilum of the left lung toward the posterior wall of the left atrium.

They lie within the thorax and pass through the pericardial reflections surrounding the venous aspect of the heart.

Formation

Pulmonary venous drainage begins in small veins receiving blood from the pulmonary capillary networks.

These veins unite into progressively larger vessels within the lung and ultimately form the major pulmonary veins at the hilum.

Intrapulmonary Veins

Within the lung, pulmonary veins commonly course in connective tissue septa between bronchopulmonary segments.

This intersegmental position contrasts with pulmonary arterial branches, which generally accompany the bronchi more centrally within bronchopulmonary segments.

Intersegmental Course

The intersegmental arrangement of pulmonary veins is an important anatomical feature.

Because these vessels often mark planes between bronchopulmonary segments, they provide useful landmarks during anatomical segmentectomy and other lung-preserving procedures.

Left Superior Pulmonary Vein

The left superior pulmonary vein drains predominantly the superior lobe of the left lung.

It is formed by tributaries draining the bronchopulmonary segments of the superior lobe and passes medially toward the left atrium.

Drainage Territory of the Left Superior Pulmonary Vein

The left superior pulmonary vein receives blood primarily from the superior lobe, including venous drainage associated with the apicoposterior and anterior regions and the lingula.

The exact pattern of tributary convergence varies between individuals.

Lingula

The lingula is part of the superior lobe of the left lung and usually drains through tributaries of the left superior pulmonary vein.

Venous channels from the superior and inferior lingular segments join the superior pulmonary venous system in variable configurations.

Left Inferior Pulmonary Vein

The left inferior pulmonary vein drains predominantly the inferior lobe of the left lung.

It receives tributaries from the superior and basal regions of the lower lobe and passes medially toward the posterior aspect of the left atrium.

Drainage Territory of the Left Inferior Pulmonary Vein

The inferior pulmonary vein receives venous blood from bronchopulmonary segments of the left lower lobe.

These include the superior segment and the basal segments, although the exact tributary arrangement varies.

Superior Segment of the Lower Lobe

Venous drainage from the superior segment of the left lower lobe contributes to the inferior pulmonary venous system.

Its tributaries join veins from the basal regions before or near formation of the left inferior pulmonary vein.

Basal Segments

The basal segments of the left lower lobe drain through intersegmental venous channels that converge toward the inferior pulmonary vein.

Patterns of convergence can differ substantially among individuals.

Course Toward the Heart

After emerging from the left lung, the superior and inferior pulmonary veins pass medially through the lung root toward the left atrium.

Their extrapulmonary portions are relatively short because of the close relationship between the lung hilum and the heart.

Root of the Left Lung

The pulmonary veins form important components of the root of the left lung.

They occupy generally anterior and inferior positions relative to several other structures of the root.

Relationship to the Pulmonary Artery

At the left lung root, the left pulmonary artery lies superior to the main bronchial structures, while the pulmonary veins generally occupy more anterior and inferior positions.

The exact spatial relationships change as the structures branch and approach the hilum.

Relationship to the Bronchi

The pulmonary veins are generally positioned anterior and inferior to the main bronchial structures at the lung root.

Within the lung, however, venous branches often run between bronchopulmonary segments rather than accompanying the bronchi directly.

Hilum of the Left Lung

The left lung hilum is the area on the mediastinal surface through which bronchi, pulmonary vessels, bronchial vessels, lymphatics, and nerves enter or leave the lung.

The pulmonary veins are among the most anterior and inferior major vascular structures visible at the hilum.

Superior and Inferior Positions

The left superior pulmonary vein generally occupies a higher position than the left inferior pulmonary vein as the vessels approach the left atrium.

The inferior pulmonary vein is particularly important as an inferior boundary of the venous reflection of the serous pericardium.

Intrapericardial Portion

Short terminal portions of the pulmonary veins lie within the pericardial sac before entering the left atrium.

Serous pericardial reflections surround their proximal cardiac ends.

Pericardial Reflections

The serous pericardium reflects around the pulmonary veins and other great vessels at the base of the heart.

These reflections contribute to formation of the oblique pericardial sinus.

Relationship to the Oblique Pericardial Sinus

The oblique pericardial sinus is a blind recess located posterior to the left atrium.

Its lateral boundaries are formed in part by serous pericardial reflections around the pulmonary veins.

Termination

The left superior and inferior pulmonary veins usually terminate separately in the left atrium.

Their openings are located on the posterior aspect of the atrium.

Left Atrial Openings

In the typical arrangement, the left atrium receives four pulmonary veins in total: two from the right lung and two from the left lung.

The left superior and left inferior pulmonary venous ostia occupy the left side of the posterior atrial wall.

Pulmonary Venous Ostia

The openings of the pulmonary veins into the left atrium are called the pulmonary venous ostia.

The size, shape, orientation, and spacing of these ostia vary between individuals.

Valves

The pulmonary veins do not possess functional valves at their junctions with the left atrium comparable to the valves found in many peripheral systemic veins.

Blood flow therefore depends primarily on pressure relationships and cardiopulmonary mechanics rather than valvular control at the atrial openings.

Function

The principal function of the left pulmonary veins is to transport oxygenated blood from the left lung to the left atrium.

From the left atrium, blood passes through the mitral valve into the left ventricle and is then ejected into the systemic circulation.

Pulmonary Circulation

The pulmonary veins form the terminal venous component of the pulmonary circulation.

Blood reaches the lungs through the pulmonary arteries, undergoes gas exchange in pulmonary capillaries, and returns to the heart through the pulmonary veins.

Oxygen Content

Pulmonary venous blood normally has a high oxygen content after gas exchange within the lungs.

This makes the pulmonary veins an important exception to the general rule that veins carry relatively deoxygenated blood.

Relationship to the Left Atrium

The left atrium forms much of the posterior surface, or base, of the heart.

Its posterior position allows the pulmonary veins to enter directly after their short course from the lung hila.

Relationship to the Esophagus

The esophagus lies posterior to the left atrium.

Because the pulmonary venous ostia are located in the posterior left atrial region, the esophagus is an important neighboring structure during procedures involving the posterior atrium and pulmonary veins.

Relationship to the Descending Thoracic Aorta

The descending thoracic aorta lies posterior and to the left of the heart and mediastinal structures.

Its relationship to the left pulmonary venous region is relevant when interpreting axial thoracic imaging.

Relationship to the Left Phrenic Nerve

The left phrenic nerve descends anterior to the root of the left lung along the fibrous pericardium.

It is therefore anterior to the pulmonary hilar structures rather than traveling directly with the pulmonary veins.

Relationship to the Left Vagus Nerve

The left vagus nerve passes posterior to the root of the left lung.

This provides an important contrast with the phrenic nerve, which passes anterior to the lung root.

Bronchial Circulation and Pulmonary Veins

Some blood from the bronchial circulation ultimately enters pulmonary veins through bronchopulmonary vascular communications.

This contributes to the small physiological difference between alveolar oxygen tension and systemic arterial oxygen tension.

Anatomical Variations

Pulmonary venous anatomy is variable.

Variations may involve the number of veins, the pattern of intrapulmonary tributaries, common trunks, accessory veins, and the size or orientation of the atrial ostia.

Left Common Pulmonary Venous Trunk

The left superior and inferior pulmonary veins may unite before entering the left atrium, producing a left common pulmonary venous trunk.

The length and diameter of such a common trunk vary.

Accessory Pulmonary Veins

Additional pulmonary venous channels may occasionally enter the left atrium separately.

Recognition of accessory veins is important before procedures involving pulmonary venous isolation or lung surgery.

Imaging

CT and MRI can demonstrate the pulmonary veins, their tributaries, and their relationship to the left atrium.

Cross-sectional and three-dimensional imaging are particularly useful for evaluating anatomical variation.

CT Angiography

Contrast-enhanced CT can provide detailed visualization of pulmonary venous anatomy.

It can demonstrate the number of veins, ostial dimensions, common trunks, accessory veins, and relationships with neighboring structures.

Cardiac MRI

Cardiac MRI can evaluate pulmonary venous anatomy and blood flow without ionizing radiation.

It can also provide functional information about the left atrium and associated cardiovascular structures.

Echocardiography

Echocardiography can assess pulmonary venous flow entering the left atrium.

Transesophageal echocardiography provides particularly useful views because the esophagus lies directly posterior to the left atrium.

Pulmonary Venous Flow

Pulmonary venous blood flow varies during the cardiac cycle and is influenced by left atrial pressure, ventricular contraction, atrial contraction, and pulmonary vascular conditions.

Doppler assessment of pulmonary venous flow can provide information about left atrial and ventricular filling dynamics.

Atrial Fibrillation

The pulmonary veins have major electrophysiological importance because myocardial sleeves from the left atrium extend for variable distances onto the pulmonary veins.

Electrical activity arising near these venous myocardial sleeves can participate in initiation of atrial fibrillation.

Myocardial Sleeves

Extensions of atrial myocardium surround portions of the pulmonary veins near their entry into the left atrium.

These myocardial sleeves provide a structural basis for electrical activity associated with pulmonary venous triggers of atrial arrhythmias.

Pulmonary Vein Isolation

Pulmonary vein isolation is a catheter ablation strategy used in the treatment of selected patients with atrial fibrillation.

The procedure creates electrical isolation around the pulmonary venous region to prevent abnormal impulses from propagating into the left atrium.

Importance of Left Pulmonary Venous Anatomy in Ablation

The dimensions and configuration of the left superior and inferior pulmonary venous ostia are important during ablation planning.

A common left pulmonary venous trunk or accessory venous anatomy can alter procedural strategy.

Pulmonary Vein Stenosis

Pulmonary vein stenosis is abnormal narrowing of a pulmonary vein.

It may be congenital or acquired and can occur as a complication of procedures involving the pulmonary venous ostia.

Effects of Pulmonary Vein Stenosis

Significant narrowing can impair venous drainage from the affected region of lung.

This can increase pulmonary venous pressure locally and may produce pulmonary congestion, edema, or other respiratory abnormalities.

Pulmonary Venous Obstruction

Obstruction of pulmonary venous drainage increases pressure upstream within pulmonary veins and capillaries.

The physiological consequences depend on the number of veins involved, severity of obstruction, and development of collateral drainage.

Anomalous Pulmonary Venous Return

In anomalous pulmonary venous return, one or more pulmonary veins connect to a systemic venous structure rather than normally entering the left atrium.

These developmental abnormalities can involve veins from either lung and vary considerably in extent.

Partial Anomalous Pulmonary Venous Return

Partial anomalous pulmonary venous return occurs when some, but not all, pulmonary veins drain abnormally into the systemic venous circulation or right atrium.

The resulting physiological effect depends on the amount of pulmonary blood returning through the anomalous pathway.

Total Anomalous Pulmonary Venous Return

Total anomalous pulmonary venous return occurs when all pulmonary venous blood reaches the systemic venous circulation rather than connecting normally to the left atrium.

It is a major congenital cardiovascular abnormality requiring communication between the right and left sides of the circulation for systemic survival.

Pulmonary Resection

Identification and control of pulmonary veins are essential during lobectomy, segmentectomy, and other pulmonary resections.

The surgeon must recognize normal and variant venous anatomy to preserve drainage from lung tissue that remains in place.

Left Upper Lobectomy

During removal of the left upper lobe, the venous drainage of the upper lobe must be distinguished from lower lobe venous channels.

Variation in tributaries can create clinically important connections between lobar territories.

Left Lower Lobectomy

During left lower lobectomy, the left inferior pulmonary vein is a major vascular structure requiring identification and control.

Recognition of a common left pulmonary venous trunk is important to avoid compromising venous drainage from the remaining upper lobe.

Segmentectomy

During anatomical segmentectomy, intersegmental pulmonary veins help define planes between bronchopulmonary segments.

Preserving appropriate venous channels is important for maintaining drainage from retained lung segments.

Thrombus and the Pulmonary Veins

Thrombus formation within pulmonary veins is uncommon compared with thrombosis in systemic peripheral veins but may occur in particular clinical settings.

Because the pulmonary veins drain directly into the left atrium, material entering this pathway has potential access to the systemic arterial circulation.

Embryological Development

The pulmonary venous system develops through incorporation of the embryonic pulmonary venous connection into the developing left atrium.

This developmental process contributes to the smooth-walled posterior portion of the mature left atrium.

Common Pulmonary Vein

Early in development, a common pulmonary venous channel establishes communication between the pulmonary venous plexus and the left atrium.

Progressive incorporation of this venous tissue into the atrial wall contributes to formation of the separate pulmonary venous openings.

Developmental Basis of Variations

Differences in incorporation and persistence of pulmonary venous channels can contribute to variations in pulmonary venous number and configuration.

Abnormal developmental connections can result in anomalous pulmonary venous return.

Left Superior and Inferior Pulmonary Veins Compared

Feature	Left Superior Pulmonary Vein	Left Inferior Pulmonary Vein
Primary drainage	Superior lobe	Inferior lobe
Major associated regions	Apicoposterior, anterior and lingular regions	Superior and basal lower-lobe regions
Termination	Posterior left atrium	Posterior left atrium
Typical relationship	Superior to left inferior pulmonary vein	Inferior to left superior pulmonary vein

Key Anatomical Relationships

Structure	Relationship
Left atrium	Receives left pulmonary veins posteriorly
Left lung	Source of pulmonary venous blood
Left lung root	Veins generally occupy anterior and inferior positions
Serous pericardium	Reflects around terminal pulmonary veins
Oblique pericardial sinus	Bounded laterally in part by pulmonary venous reflections
Esophagus	Posterior to left atrium and relevant to pulmonary venous procedures

Key Features of the Left Pulmonary Veins

Feature	Key Point
Typical number	Two
Names	Left superior and left inferior pulmonary veins
Blood carried	Oxygenated blood
Origin	Venous networks of left lung
Termination	Left atrium
Intrapulmonary course	Predominantly intersegmental
Valves at atrial openings	No functional valves
Important variation	Common left pulmonary venous trunk
Major clinical relevance	Atrial fibrillation ablation, pulmonary surgery and pulmonary venous obstruction

Anatomical and Clinical Importance

The left pulmonary veins provide the final vascular pathway carrying oxygenated blood from the left lung into the left atrium. Their intrapulmonary tributaries commonly occupy intersegmental planes, while their major superior and inferior trunks pass through the left lung root and terminate on the posterior atrial wall.

Their anatomy is closely linked to the organization of the left lung, pericardial reflections, and posterior left atrium. Variations such as a common left pulmonary venous trunk or accessory veins are important because they can alter the expected arrangement of the vessels during imaging and surgery.

The left pulmonary veins are also important electrophysiological structures. Myocardial extensions around their proximal portions can participate in atrial arrhythmias, making the pulmonary venous ostia major landmarks in catheter ablation for atrial fibrillation. Accurate knowledge of their anatomy is therefore essential in cardiovascular imaging, electrophysiology, and thoracic surgery.