bubble_chart Overview

Pulmonary arteriovenous fistula is a congenital pulmonary vascular malformation. The blood vessels dilate, become tortuous, or form cavernous hemangiomas. Pulmonary arterial blood flows directly into the pulmonary veins without passing through the alveoli, creating a shunt where the pulmonary artery and veins directly connect. It was first described by Churton in 1897 as multiple pulmonary artery aneurysms. In 1939, Smith confirmed the disease using cardiac angiography. The literature has various names for this condition, such as pulmonary arteriovenous aneurysm, hemangiectasis of the lung, and capillary telangiectasia with pulmonary artery aneurysm. Additionally, this disease has a familial tendency and is associated with genetic factors, such as hereditary hemorrhagic telangiectasia (Rendu-Osler-Weber disease).

bubble_chart Pathological Changes

This malformation involves direct connections between pulmonary arteries and veins of varying sizes and unequal numbers. The most common configuration is one artery and two veins. There is no capillary bed between them. The affected vessel walls have poorly developed muscular layers and lack elastic fibers. Additionally, the pressure from the pulmonary artery causes progressive dilation of the affected vessels. Pulmonary arteriovenous aneurysm is a type of direct communication between pulmonary arterial and venous branches, characterized by tortuous and dilated vessels, thin arterial walls, thick venous walls, and sac-like dilation of the aneurysm with septations and visible thrombi. The lesions can occur in any part of the lung. The aneurysm walls may thicken, but in some areas, the endothelial layer is reduced, degenerated, or calcified, which can lead to rupture. A rare and special type involves direct communication between the right pulmonary artery and the left atrium.

The lesions may be distributed in one or both lungs, single or multiple, ranging in size from 1 mm to involving the entire lung. They are commonly found in the subpleural regions of the right and bilateral lower lobes and the right middle lobe. Approximately 6% of cases are associated with Rendu-Osler-Weber syndrome (multiple arteriovenous fistulas, bronchiectasis or other malformations, absence of the right lower lobe, and congenital heart disease).

The main pathophysiological feature is the shunting of venous blood from the pulmonary artery into the pulmonary vein, with a shunt volume ranging from 18% to 89%, leading to decreased arterial oxygen saturation. Generally, there is no ventilation impairment, and PCO₂ remains normal. Most cases develop polycythemia due to hypoxemia. Additionally, the direct communication between the pulmonary and systemic circulations increases the risk of bacterial infections, brain abscesses, and other complications.

bubble_chart Clinical Manifestations

This disease is commonly seen in young adults. Patients with small shunts may be asymptomatic and only detected during pulmonary X-ray examinations. Those with large shunts may experience dyspnea after activity and cyanosis, which mostly appear during childhood and occasionally in newborns. Hemoptysis is caused by the rupture of telangiectatic lesions in the bronchial mucosa or pulmonary arteriovenous fistulas. Chest pain may result from bleeding due to lesion rupture beneath the visceral pleura or hemothorax. Approximately 25% of cases present with neurological symptoms, such as spasms, speech disorders, diplopia, and transient numbness, which may be caused by polycythemia, hypoxemia, vascular embolism, brain abscesses, or bleeding from cerebral telangiectatic lesions. In hereditary hemorrhagic telangiectasia, bleeding symptoms such as epistaxis, hemoptysis, hematuria, vaginal bleeding, and gastrointestinal bleeding are common. The presence of fistulas may also lead to bacterial endocarditis. Careful auscultation over the affected area reveals systolic or continuous murmurs in about 50% of cases, characterized by increased intensity during inspiration and decreased intensity during expiration. Other manifestations include clubbing of fingers and toes, polycythemia, increased hematocrit, and decreased oxygen saturation in the stirred pulse.

Classification:

Type I Multiple telangiectasia: Diffuse and multiple, formed by anastomoses of capillary terminals, with large shunt volumes.

Type II Pulmonary stirred pulse tumor: Formed by anastomoses of larger, more central vessels, exhibiting aneurysmal dilation due to pressure factors, with even larger shunt volumes.

Type III Communication between pulmonary stirred pulse and left atrium: The pulmonary stirred pulse is significantly enlarged, with extremely large shunt volumes, where right-to-left shunting may account for 80% of pulmonary blood flow, often accompanied by abnormalities in pulmonary lobes and bronchi.

bubble_chart Auxiliary Examination

The X-ray findings {|###|} show normal heart size, but in cases of pulmonary arteriovenous fistula with large shunting, cardiac enlargement may occur. Approximately 50% of cases exhibit single or multiple mass-like, spherical, nodular, or speckled shadows of varying sizes on chest radiographs, located in one or multiple lung fields. The affected vessels appear as cord-like radiopaque shadows extending from the fistula toward the hilum, with calcification being rare. Rib erosion may result from the expansion of intercostal {|###|} stirred pulse, though this is uncommon. During fluoroscopy for {|###|} seasonal disease, performing the Valsalva maneuver, which increases intrathoracic pressure, may cause the arteriovenous aneurysm to shrink. Definitive localization relies on {|###|} heart blood angiography. {|###|} Cardiac catheterization and {|###|} heart blood angiography {|###|} reveal decreased oxygen saturation in the {|###|} stirred pulse. Cardiac output and chamber pressures are normal, with no evidence of intracardiac shunting. The dye dilution test can be used to assess shunt volume and location, with caution to avoid catheter entry into the fistula and the risk of rupture. Injection of contrast medium into the pulmonary {|###|} stirred pulse can delineate the site and size of the arteriovenous fistula, showing dilated, elongated, and tortuous vessels.

bubble_chart Treatment Measures

All patients with symptoms and localized lesions require surgical treatment. Even in the absence of obvious symptoms, due to the progression of sexually transmitted disease changes, life-threatening complications such as rupture, hemorrhage, bacterial endocarditis, brain abscess, and embolism may occur, necessitating surgical intervention. Surgery is not recommended only for extremely small fistulas or cases with diffuse bilateral lung involvement. For infants and young children with mild symptoms, surgery can be performed during childhood.

The surgical approach depends on the size, number, and type of lesions. Pulmonary resection is the most commonly used method, including wedge resection, segmental resection, lobectomy, and pneumonectomy. The principle is to minimize lung tissue removal and preserve pulmonary function. During the procedure, the stirred pulse should be ligated first, and caution should be exercised to prevent bleeding when handling adhesions. When a fistula caused by abnormal blood vessels is identified, ligation of the abnormal vessels is the simplest and most effective approach. If the abnormal vessels cannot be resected or ligated, an intraluminal closure of the stirred pulse aneurysm can be performed.