All you need to know about the pulmonary veins and diseases that affect them

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All you need to know about the pulmonary veins and diseases that affect them

Veins are the blood vessels that carry blood to the heart. The pulmonary veins are the veins that transfer oxygenated blood from the lungs to the heart.

The largest pulmonary veins are the four main pulmonary veins, two from each lung that drains into the left atrium of the heart.

The pulmonary veins are part of the pulmonary circulation. This differentiates the pulmonary veins from other veins in the body, which are used to carry deoxygenated blood from the rest of the body back to the heart.

What is Pulmonary Circulation

The pulmonary circulation is the portion of the circulatory system which carries deoxygenated blood away from the right ventricle, to the lungs, and returns oxygenated blood to the left atrium and ventricle of the heart.

The vessels involved in pulmonary circulation are the pulmonary arteries and pulmonary veins.

The Pulmonary Veins Structure

 Humans have four pulmonary veins in total, two from each lung.

There are two right pulmonary veins, known as the right superior and right inferior veins. These carry blood from the right lung.

Each pulmonary vein is linked to a network of capillaries (small blood vessels) in the alveoli of each lung. Alveoli are tiny air sacs within the lungs where oxygen and carbon dioxide are exchanged.

These capillaries eventually join together to form a single blood vessel from each lobe of the lung. The right lung contains three lobes, while the left lung is slightly small and contains only two lobes.

Initially, there are three vessels for the right lung, but the veins from the middle and upper lobes of the right lung tend to fuse together to form two right pulmonary veins.

The right pulmonary veins pass behind the right atrium and another large blood vessel known as the superior vena cava.

The function of the Pulmonary Veins

The pulmonary veins are very important in respiration. They receive blood that has been oxygenated in the alveoli and returns it to the left atrium.

Clinical significance of the Pulmonary Veins

The pulmonary veins being part of the pulmonary circulation means that they carry oxygenated blood back to the heart, as opposed to the veins of the systemic circulation which carry deoxygenated blood.

A genetic defect of the pulmonary veins which is rare and is known as a total anomalous pulmonary venous connection (or drainage) or partial anomalous pulmonary connection can cause them to drain into the pulmonary circulation in whole or in part, respectively.

Diseases that affect the Pulmonary Veins

 Pulmonary vein disease can be broadly classified into congenital or acquired conditions.

Congenital disease, which often goes unnoticed until patients are adults, mainly includes

  • Anomalies in the number or diameter of the vessels
  •  Abnormal drainage or connection with the pulmonary arterial tree.

The acquired disease can be grouped into

(1)Stenosis and Obstruction:

Pulmonary vein stenosis and/or obstruction is a very rare and serious condition in which there is a blockage in the blood vessels that bring oxygen-rich blood from the lungs back to the heart.

Pulmonary vein stenosis or obstruction often has important clinical repercussions and is frequently a result of radiofrequency ablation complications, neoplastic infiltration, or fibrosing mediastinitis.

This condition can be isolated to one vein, but often affects multiple veins. Stenosis occurs when there is an abnormal thickening and narrowing of the walls of the veins. Pulmonary vein stenosis is a progressive condition and may lead to total obstruction to a blood vessel.

Most commonly, all of the pulmonary veins of one lung are affected, causing pulmonary hypertension and pulmonary arterial hypertension.

Surgery and catheterization to widen the narrow veins is usually a short-term solution since the obstruction typically reoccurs.

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(2) Hypertension

This is the increased blood pressure in the pulmonary veins (carrying blood away from the lungs, to the heart). Pulmonary venous hypertension is most commonly caused by chronic left ventricular failure (congestive heart failure).  A damaged mitral valve in the heart (mitral stenosis or mitral regurgitation) may contribute to pulmonary venous hypertension.

This condition is difficult to differentiate from veno-occlusive pulmonary disease, which requires a completely different treatment.

(3) Thrombosis:

Pulmonary vein thrombosis is a rare, but severe condition that can have a local or distant cause; its incidence is unclear, as most of the literature includes case reports.

It most commonly occurs as a complication of malignancy, post lung surgery, or atrial fibrillation and can be idiopathic in some cases

Most patients with PVT are commonly asymptomatic or have nonspecific symptoms such as cough, hemoptysis, and dyspnea from pulmonary edema or infarction.

The thrombi are typically detected using a variety of imaging modalities including a transesophageal echocardiogram (TEE), computed tomography (CT) scanning, magnetic resonance imaging (MRI), or pulmonary angiography.

Treatment should be determined by the obstructing pathological finding and can include antibiotic therapy, anticoagulation, thrombectomy, and/or pulmonary resection.

The delay in diagnosing this medical entity can lead to complications including pulmonary infarction, pulmonary edema, right ventricular failure, allograft failure, and peripheral embolism resulting in limb ischemia, stroke, and renal infarction (RI).

(4) Calcifications:

Calcifications have been described in rheumatic mitral valve disease and chronic renal failure.

Pulmonary vein calcification in long-term rheumatic mitral valve disease is associated with atrial fibrillation, considerable left atrial dilatation, a high prevalence of dyspnea, and a female predominance.

While calcifications related to chronic renal failure are associated with cardiac arrhythmias and are due to deposits of extraskeletal metastatic calcium.

Pulmonary vein calcifications may be more prevalent in patients with atrial fibrillation, and these calcifications play a role in the pathogenesis of atrial fibrillation.

The CT diagnosis of pulmonary vein calcifications is based on the presence of left atrial dilatation and extensive calcifications in the left atrial wall.

The calcifications sometimes occur in the form of “moldlike” calcifications that extend into the interatrial septum and the distal portion of the pulmonary vein.

(5) Collateral Circulation:

The pulmonary veins can act as conduits for collateral circulation in cases of obstruction of the superior vena cava.

Systemic-to-pulmonary venous shunts sometimes develop in cases of superior vena cava obstruction, usually as a result of malignant causes, although such shunts may also be secondary to benign conditions.

Systemic-to-pulmonary venous shunts are observed in 9% of cases of superior vena cava syndrome with collateral circulation.

Systemic-to-pulmonary venous shunts can be anatomic, congenital, or acquired.

In the anatomic type, the bronchial veins and pulmonary veins are connected through a preexisting bronchial venous plexus located in the bronchial walls and peribronchovascular connective tissue.

 In the congenital type, there are three mechanisms of development:

(a) Anomalous pulmonary venous return with inverse blood flow.

(b) An embryologic levoatriocardinal vein remnant that connects the posterior cardinal venous system to the pulmonary vein.

(c) A persistent left superior vena cava.

The acquired type of systemic-to-pulmonary venous shunt consists of inflammation-induced newly formed vessels that connect subpleural portions of the pulmonary veins to intercostal veins through pleural adhesions.

Imaging of the Pulmonary Veins

 Several imaging modalities are used to assess the pulmonary veins, including chest radiography, echocardiography, magnetic resonance (MR) imaging, and computed tomography (CT).

Multidetector CT is an excellent technique for imaging evaluation of the pulmonary veins, even when the examination is not specifically tailored for their assessment and is currently available in many radiology departments worldwide.

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Conclusion

The pulmonary veins are relatively large structures relative to other veins running as large as 1 centimeter in diameter.

Though they are sometimes smaller in women. They are made up of three layers of smooth muscle tissue called tunics.

The outer layer is the thick tunica externa, with the middle layer the thin tunica media, followed by the central layer of the tunica intima.

The pulmonary veins may also be damaged during surgical procedures. This includes the different types of surgery for lung cancer.

The pulmonary veins are essential for pulmonary circulation hence, any rupture or anomaly will have severe consequences.

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