Pulmonary arteriovenous fistula is a congenital pulmonary vascular malformation. The blood vessels are enlarged or distorted or form a cavernous hemangioma. The pulmonary blood flows directly into the pulmonary vein without passing through the alveoli, and the pulmonary artery directly communicates with the vein to form a short circuit. First described in 1897 by Churton, known as multiple pulmonary aneurysms. In 1939, Smith applied cardiovascular angiography to confirm the disease. There are many literature names, such as pulmonary arteriovenous tumor, pulmonary vasodilatation (haemagiectasis of the lung), telangiectasia with pulmonary artery aneurysm (haemonreac telangiectasia with pulmonary artery aneurysm). In addition, the disease is familial and is associated with genetic factors such as hereditary hemorrhagic telangiectasia (Rendu-Osler-Weber disease).
This malformation is directly connected by a variety of different sizes and unequal numbers of pulmonary arteries and veins. Commonly, one artery and two veins. There is no capillary bed between the two. The muscular wall of the diseased vessel wall is poorly developed, lacking elastic fibers, and the pulmonary artery pressure promotes the progressive expansion of the diseased blood vessels. Pulmonary arteriovenous sinus is a type of direct arteriovenous branch, which is characterized by vascular distortion, dilatation, thin arterial wall, thick vein wall, cystic enlargement of the tumor, and tumor separation. The lesion can be located in any part of the lung, and the wall of the tumor is thickened, but the endothelial layer is reduced, denatured or calcified in a certain area, which is the cause of the rupture. There is also direct traffic between the right pulmonary artery and the left atrium, which is a rare special type.
The lesions are distributed on one or both sides of the lung, single or multiple, and may be 1 mm in size or involving the entire lung, the subpleural area of the right and second lower lobe, and the right middle lobe. About 6% of the disease is associated with Rendu-Osler-Weber syndrome (multiple arteriovenous fistula, bronchiectasis or other malformations, lack of right lower lobe and congenital heart disease).
The main pathophysiology is that venous blood flows from the pulmonary artery into the pulmonary artery, and its partial flow can reach 18 to 89%, so that the arterial oxygen saturation decreases. Generally no ventilation disorder, PCO2 is normal. In most cases, erythrocytosis is caused by hypoxemia, and direct traffic is caused by lungs and systemic circulation, which may cause complications such as bacterial infection and brain abscess.
Ultrasound diagnosis of cardiovascular disease
The heart shadow is normal, but the pulmonary arteriovenous fistula with large flow rate has a heart enlargement. About 50% of cases show single or multiple lumps, globular, nodular, and speckled shadows on the chest radiograph, ranging in size from one or more lung fields. The diseased blood vessels are rope-like opaque shadows, extending from the ankle to the hilar, and calcification is rare. Rib erosion can be caused by the enlargement of the intercostal artery, but it is not common. The patient does Valsalva movement during fluoroscopy. When the intrathoracic pressure is increased, the arteriovenous tumor is reduced. Positional diagnosis relies on cardiovascular angiography.
Cardiac catheterization and angiography
Arterial oxygen saturation decreased. There is no intracardiac shunt in the heart beat volume and heart chamber pressure. The pigment dilution test can be used to test the flow rate and location, taking care to avoid the catheter entering the sputum and alert to the risk of rupture. Intra-arterial injection of contrast agent can show the location and size of arteriovenous fistula, showing dilated, elongated, and distorted blood vessels.
The disease is more common in young people, and the small flow rate can be asymptomatic, only found in the X-ray examination of the lungs. Those with large flow rate may have shortness of breath and cyanosis after the activity, but most of them appear in childhood, occasionally in newborns. Hemoptysis is caused by a lesion of the telangiectasia lesion located in the bronchial mucosa or a rupture of the pulmonary arteriovenous fistula. Chest pain can be caused by rupture of the lesion in the subpleural or hemothorax of the lung. About 25% of cases have neurological symptoms such as convulsions, speech disorders, diplopia, temporary numbness, etc., which can be caused by erythrocytosis, hypoxemia, vascular embolism, brain abscess and cerebral telangiectasia. Hemorrhagic telangiectasia associated with familial inheritance often has bleeding symptoms such as epistaxis, hemoptysis, hematuria, vaginal and gastrointestinal bleeding. Bacterial endocarditis can also be complicated by the presence of sputum. Careful auscultation in the lesion area, about 50% of cases can hear systolic murmur or two-stage continuous murmur, which is characterized by increased noise with inhalation and decreased exhalation. Others include clubbing, erythrocytosis, increased hematocrit, and decreased arterial oxygen saturation.
Type I: multiple telangiectasia: diffuse, multiple, formed by capillary terminal anastomosis, with a large short-circuit flow.
Type II: Pulmonary aneurysm: formed by an anastomosis of a larger vascular near the center, due to pressure factors, tumor expansion, and short-circuit flow.
Type III: Pulmonary artery and left atrial communication: The pulmonary artery is significantly enlarged, and the short-circuit flow is extremely large. The right-to-left flow can account for 80% of the pulmonary blood flow, often accompanied by abnormalities of the lung and bronchus.