Pulmonary arteriovenous fistula is a rare pulmonary disease, first identified by Churton in 1897 during autopsy and first reported clinically by Smith in 1939. Few cases have been reported in China, mostly as case reports. However, with the improvement of medical equipment and the accumulation of experience, the number of cases has gradually increased.
I. The causes of pulmonary arteriovenous fistula are not well understood
Congenital factors: Inadequate development or degeneration of the vascular compartment of the germinal pulmonary arteriovenous plexus and defects in the vascular collaterals form thin-walled hemangiomas, which cause short-circuiting of the arteries and veins and lead to a series of pathophysiological changes.
Pulmonary arteriovenous fistulas are associated with hereditary capillary dilation (HHT), characterized by recurrent bleeding from various internal organs (epistaxis is more common) and capillary dilation of the skin, mucous membranes, and internal organs.HHT is an autosomal dominant disorder associated with mutations in the autosomal 9q3 and 12q genes.
Pulmonary arteriovenous fistulas are often combined with other congenital disorders such as arteriovenous ductus arteriosus (3 cases in this group), atrial septal defect, ventricular septal defect, corporal arteriovenous fistula, and ectopic drainage of the left atrium of the inferior vena cava (1 case each in this group).
Acquired factors: PAVF can be caused by trauma and surgery, and cirrhosis combined with intrapulmonary shunt is also an acquired factor, often occurring from 6 months to 14 years of age; children may have cyanosis, dyspnea, or both. In children with biliary obstruction and multiple spleen syndrome, symptoms appear earlier. Pregnancy can aggravate PAVF (four cases in our group), and rheumatic heart disease combined with valvular disease also makes PAVF symptoms more pronounced, both of which are acquired factors.
II. Typology of pulmonary arteriovenous fistula
Angiomatous (cystic) (isolated or multiple), diffuse pulmonary arteriovenous fistula; pulmonary artery-left atrial fistula (one case in this group).
Pathologic histologic features
Pulmonary arteriovenous fistulas can vary in diameter from 1 mm to several centimeters, mostly located near the subpleural or tracheal vascular bundles, forming a cystic structure with extremely thin, dark purple walls, and tremors can be felt on the surface.
There are thick blood supply and drainage vessels. The histology consists of different proportions of vascular mesothelial cells, vascular ducts and connective tissues, and the tumor-like dilated capsule wall has elastic fibers and smooth muscle cells.
IV. Clinical manifestations
Mainly exertional dyspnea; if the disease is mild and symptoms are not obvious it is often missed or misdiagnosed as tuberculosis or multiple metastases, and the history can be as long as 30 years; many patients have no pulmonary symptoms, and often pulmonary arteriovenous fistulae are found due to epistaxis, vomiting blood, hemoptysis, hemothorax, syncope, erythrocytosis and cerebral embolism. If the history is long and the disease is severe, clinical cyanosis and pestle-like toes are evident and often misdiagnosed as cyanotic congenital heart disease; pulmonary arteriovenous fistulae close to the chest wall can be heard locally as a vascular murmur.
V. Radiological imaging
The typical angiomatous PAVF shows a round or oval lobulated shadow with a diameter ranging from 1 mm to several centimeters, mostly located in the lower lobe. The blood supply and drainage vessels can be identified on plain film and tomography, and shadow pulsation can be observed under fluoroscopy, and the pulsation of vessels in the affected pulmonary hilum is more obvious than that in the healthy side.
VI. Echocardiographic sonography
It is the most convenient and less invasive method to determine pulmonary arteriovenous fistulae and is very useful to determine extracardiac right-to-left shunts. The method is to determine the intrapulmonary arteriovenous shunt by injecting saline containing microbubbles after shaking through the anterior elbow vein, and the right heart is visualized for 3-4 cardiac cycles and then the left heart is visualized. The disadvantage is that the location and extent cannot be determined, and the shunt flow cannot be measured.
VII. Pulmonary perfusion imaging is highly sensitive and can determine the site and extent, and determine the fractional flow.
The method is to inject 99mTc-albumin (7~25μm in diameter) into the peripheral vein, and the fraction of fractional flow can be measured by following the blood flow from the lungs to the brain and kidneys. The advantage is that it is more suitable for fractional flow measurement during exercise. The disadvantage is that it cannot distinguish between intrapulmonary and intracardiac shunts and cannot observe specific anatomical details, and it is also more expensive.
MRI is a non-invasive method of examination
It is easier to detect and identify pulmonary arteriovenous fistulas, and can clarify the site, morphology, and extent of involvement of the lesion, and can show the blood supply and drainage vessels.
Nine, spiral CT angiography can show the vascular structure from all angles, with high accuracy, and has obvious advantages
Advantages: It is a non-invasive examination and does not require the insertion of a catheter. The disadvantage is that it requires longer breath-holding time, otherwise the examination effect is affected; the spatial resolution of large pulmonary arteriovenous fistula is poor.
X. High temporal and spatial resolution of pulmonary arteriography
Superselective angiography is more sensitive and remains the gold standard for diagnosing pulmonary arteriovenous fistulas. Digital subtraction angiography can identify and localize vascular malformations and can even be used for simultaneous embolization therapy. But there are invasive tests.
XI. Treatment
Surgical resection of the malformed vessels is the radical treatment (29 cases in our group), either lobar (11 cases), segmental (1 case) or partial resection (5 cases) depending on the size of the lesion, but total lung resection should be done with caution (2 cases) and it must be determined that the contralateral lung is completely normal. Severe pulmonary arteriovenous fistula is an indication for bilateral lung transplantation, and single lung transplantation cannot be performed and should be strictly controlled. In order to preserve as much lung tissue and lung function as possible, resection of pulmonary arteriovenous fistula tumors should be pursued. Pulmonary arteriovenous fistulas closer to the pulmonary hilum can be treated with input artery ligation (2 cases), but the long-term results are controversial.
Pulmonary arteriovenous fistulas are mostly located under the dirty pleura and the tissue around the fistula is very thin, which can easily rupture and bleed. Careful dissection, careful operation and preparation to block the pulmonary artery trunk are necessary during surgery. In addition, the collateral circulation is abundant and care should be taken to prevent bleeding. Anesthesia is performed with double-lumen tracheal intubation to ensure normal ventilation on one side and to prevent intraoperative bleeding and asphyxia.
Embolization of pulmonary arteriovenous fistulas (4 cases in this group): Pulmonary arteriovenous fistulas with diameters greater than 3 mm and less than 15 mm are suitable for embolization, which can be done with polyethylene alcohol, wool plugs, stainless steel plugs, detachable balloons, controlled spring steel rings, etc. However, the pulmonary artery branches rapidly, embolization is difficult to locate, and the technical requirements are high; the pulmonary artery wall is thin and dilated, the embolus is not easy to fix, and the pulmonary arteriovenous fistula has no barrier effect, so it is easy to dislodge and misembolize. Embolization treatment requires certain equipment, and requires more experience. Surgical resection should be considered if the diameter is large, the structure is complicated or a lung abscess is formed.