What Is Pulmonary Arteriovenous Malformation?

Pulmonary arteriovenous malformation (pulmonaryarteriovenousmalformation, PAVM) is a typical disease caused by congenital dysplasia. About 70% of patients with PAVM are complicated by hereditary hemorrhagic telangiectasia. Genetics believes that chromosomal abnormalities can cause the disease. Some authors believe that PAVM may be caused by trauma, schistosomiasis and tumors. The basic pathological change is that the artery passes directly into the enlarged vein through only the thin aneurysm sac.

Pulmonary arteriovenous malformation

Pulmonary arteriovenous malformation (pulmonaryarteriovenousmalformation, PAVM) is a typical disease caused by congenital dysplasia. About 70% of patients with PAVM are complicated by hereditary hemorrhagic telangiectasia. Genetics believes that chromosomal abnormalities can cause the disease. Some authors believe that PAVM may be caused by trauma, schistosomiasis and tumors. The basic pathological change is that the artery passes directly into the enlarged vein through only the thin aneurysm sac.

Chinese name

Pulmonary arteriovenous malformation

Foreign name

(pulmonaryarteriovenousmalformation, PAVM

Cause

PAVM can have trauma, schistosomiasis and tumors

Types of

A disease

1. There is often a small amount of hemoptysis, which can cause bloody pleural effusion after rupture, and a large amount of hemoptysis when broken into the large bronchus.

2. Hypoxemia cyanosis, clubbing fingers, fatigue, reduced workload capacity.

3. Ectopic embolism such as cerebral infarction, brain abscess.

4. When arteriovenous malformations are close to the chest wall, noise can be heard.

X-ray:

1. Chest radiographs and nodular shadows in the lung field, thick vascular shadows between the lesion and the hilum, most of the lesions have pulsation under the perspective.

2.DSA inspection

1) Solitary or clustered nodular blood vessels of different sizes or similar.

2) Diffuse capillaries.

3) The scattered distribution is connected with a single large pulmonary artery, and the corresponding pulmonary veins are filled in advance.

CT:

1. A leaf-shaped round or oval lesion with abnormal "vascular pedicle signs" connected to the hilum at the edge (Figure 8-2-3A8-2-3B8-2-3C8-2-3D8-2-3E8 -2-3F).

2. After enhancement, the lesions are simultaneously enhanced with the pulmonary arteries, and the draining veins and left atrium develop early.

3. MPR showed abnormal blood vessel shadows connected with the hilum.

About 80% of PAVMs are congenital. This malformation is an abnormal development of pulmonary capillaries. During the embryonic development, the venous plexus around the lung buds coincides with the sixth pulmonary artery tree derived from the aortic arch. With the development of the embryo, the vascular bed here appears vascular space, forming pulmonary capillaries, so the original arteriovenous plexus at the level of lung buds is separated. Once the formation of the above vascular space is impaired, the development of pulmonary capillaries is incomplete One or more pulmonary arteriovenous fistulas appear. Studies have found that most congenital PAVMs are associated with HHT, which is an autosomal dominant genetic disease. At present, HHT is known to be related to at least three genetic loci on the chromosome, the latter HHT1 is caused by a gene mutation on the chromosome 9q3 locus, and HHT2 is caused by a gene mutation on the chromosomal locus. At the same time, about 15% -35% of HHT were found to be associated with PAVMs, so some people speculate that PAVMs are also a genetic disease caused by genetic mutations.

PAVMs can also be caused by acquired lesions, such as cirrhosis, trauma, surgery, mitral valve stenosis, tuberculosis, schistosomiasis, and metastatic thyroid cancer. In addition, pregnancy can lead to faster growth of PAVMS, leading to related complications.

PAVMs are common in the lower lobe of both lungs, mostly unilateral lesions, and only 8-10% are bilateral lesions. About 50-75% are single and 30% are multiple. Single lesions are most commonly found in the lower lobe of the left lung, followed by the right lower lobe, upper left lobe, right middle lobe, and right upper lobe. Multiple lesions are more common in both lower lungs, with about 8-20 being affected on both sides simultaneously. %, Fistula more accepts the pleura, rare in the lung parenchyma.

There are two types of pathology, namely cystic and diffuse. The former fistula tract forms a curled hemangioma sac with uneven thickness of the tumor wall, which is divided into simple type and complex type. In the simple type, one blood supply pulmonary artery communicates directly with one draining pulmonary vein, and the tumor sac is not separated; in the complex type, more than two blood supply pulmonary arteries directly communicate with the draining pulmonary vein, and the sac cavity is often separated. Diffuse type can be confined to one lobe or throughout both lungs, with only small fistula tracts connecting arteriovenous, without tumor sac formation. The study found that approximately (80-90%) of PAVMs are of the simple type, and approximately 95% of PAVMs are supplied by the pulmonary artery, and the rest are supplied by the systemic circulation artery or both. Arteries involved in systemic blood supply include abnormal branches such as the thoracic aorta, internal mammary artery, intercostal artery, and coronary artery. A few diseases are combined with pulmonary vein abnormalities.

Pulmonary arteriovenous abnormal structures are often latent in the early postnatal period, and then the disease gradually develops and expands under the action of pulmonary artery pressure, and the tumor wall also has corresponding secondary deforming changes. In case of chest trauma, the thin degenerative cystic fistula is easy to rupture, leading to major hemorrhage, hemothorax or hemoptysis, and then localized hemosiderinosis.

PAVMs generally do not affect the heart's hemodynamics, cardiac output, cardiac index, and pulmonary capillary wedge pressure in the normal range, so heart rate, blood pressure, and electrocardiogram are mostly normal. However, individual reports of cardiac index may increase or decrease. Part of the pulmonary arterial blood does not exchange gas with the alveoli, directly enters the pulmonary veins, returns to the left heart, and enters the systemic circulation to form a pathological arteriovenous shunt, which is hemodynamically classified as an extracardiac right-to-left shunt, making both PAVMsSaO2 and oxygen saturation There are varying degrees of decline.

Since the oxygen partial pressure between normal arterial and venous blood reaches 50 mmHg, and the carbon dioxide partial pressure is only 6 mmHg, after the venous blood enters the arterial system during arteriovenous shunt, the oxygen partial pressure in the mixed blood decreases more than the carbon dioxide partial pressure increases. And because of the different dissociation curves of oxygen and carbon dioxide, the body produces different compensation effects for hypoxia and carbon dioxide retention. Hypoxia reflexively deepens breathing, but the blood flowing through the capillaries of the ventilated alveoli has reached a high oxygen saturation level, and the blood oxygen content will not increase significantly. The carbon dioxide dissociation curve is basically linear in the physiological range, so more carbon dioxide can be emitted after increased ventilation. In addition, because carbon dioxide molecules diffuse through the alveolar membrane 20 times more than oxygen, the partial pressure of carbon dioxide in arterial blood of patients with PAVMs can be normal, or even decreased. The slight decrease in partial pressure of carbon dioxide caused by a slight PAVMS is not clinically detectable. Large PAVMS significantly reduces the partial pressure of oxygen and often causes erythrocytosis. Therefore, although the partial pressure of oxygen and saturation are lower than normal, the blood oxygen content can still be normal or close to normal.

Although PAVMs are congenital diseases, they rarely occur in infants and young children, and the related symptoms often appear at the age of 40-60 years. However, it may be due to the small PAVMs in childhood, which do not cause significant hemodynamic changes, and X-ray examination. Not easy to find.

The severity of PAVMs symptoms is closely related to the size of the lesion. Some patients (13-55%) were asymptomatic and were occasionally found on X-ray examination. Patients with HHT often have multiple PAVMs, and the lesions are mostly rapid progressing. Fistula sacs can increase, symptoms are more common, and the incidence of complications is high.

In general, a single isolated PAVMS with a diameter of less than 2 cm does not cause symptoms. Multiple patients are more likely to have clinical symptoms than single patients, while patients with diffuse PAVMs have no exceptions.

Breathing difficulties can occur when the shunt volume is greater than 20% and the elderly have a history of the disease. It is the most common and early-onset symptoms in the clinic. It is slightly better at rest and worsens after activity. Symptoms refer to almost all patients. The degree of dyspnea is related to the severity of hypoxemia and the magnitude of the right-to-left shunt. Hypoxemia is well tolerated in most patients. Hypoxic symptoms usually occur only when the oxygen partial pressure is below 60mmHg, followed by epistaxis, which is characterized by spontaneous or slight touch, and is caused by the nose. Caused by mucosal capillary dilatation and bleeding, this manifestation reflects the high incidence of HHT in patients with PAVMs; the third is hemoptysis, large hemoptysis is rare, but rarely causes disease; again, skin, gastrointestinal tract capillary bleeding , Chest pain, cough, migraine, tinnitus, dizziness, etc.

Common signs include cyanosis and club-shaped fingers (toes). When the murmur at the diseased site appears when the right-to-left partial flow is large, occasionally tremor can be touched. It is reported that through careful physical examination, more than 75% of patients can be found abnormally. About 46% of PAVMS can hear continuous or systolic vascular murmurs in the chest. The degree of murmurs depends more on the pressure difference between arterial and venous, not necessarily related to the size of the fistula. The murmur increases during inhalation and decreases during exhalation (the reason is that the pleural cavity negative pressure increases during inhalation, the capillary blood content in the lungs increases, and the volume of blood returned from the pulmonary veins to the systemic circulation is less than that of the right ventricle into the pulmonary circulation The arterial blood pressure in the systemic circulation is reduced, the difference between the arterial pressure in the systemic circulation and the pulmonary circulation is reduced, and the blood flow of the pulmonary arteriovenous malformation is increased, but the opposite is true when exhaling). Because PAVMs are mainly lesions of the lower lobe of the lung, patients may present with orthostatic hypoxemia.

PAVMs can cause serious complications, but proper treatment can often prevent them. The most common is a neurological complication, with an incidence of about 30%, especially in patients with diffuse PAVMS. These included stroke (18%), migraine (43%), transient ischemic attack (37%), brain abscess (9%), and seizures (8%). It is reported in the literature that almost all complications of the nervous system occur in those with a diameter of the supplying artery> 3mm.

In addition, pulmonary hypertension, paradoxical embolism, infective endocarditis, anemia, hemoptysis, hemothorax, and erythrocytosis can be complicated. Hemothorax is generally caused by rupture of PAVMs under the pleura to the pleural cavity, and hemoptysis It is caused by PAVMS rupture to rupture of bronchi or dilated capillaries in the bronchi, both of which are life-threatening complications. Paradoxical embolism is the most common cause of non-infectious cerebrovascular accidents. The incidences of erythrocytosis and anemia were 25% and 17%, respectively. Erythrocytosis and coexisting brain AVMs are the rare causes of cerebrovascular accidents. The cause of pulmonary hypertension is not clear. Some literatures suggest that it is related to chronic hypoxemia, which can cause PAVMS to increase quickly and make the disease worse. Individually associated with pulmonary osteoarthropathy.

There are many methods for diagnosing PAVMs. Now, the most sensitive methods commonly used in clinical practice are summarized as follows:

Chest X-ray is simple, sensitive, non-invasive and economical. It is currently used as a first-line screening test for PAVMS. Chest radiographs have been reported to be abnormal in approximately 98% of patients. Cystic PAVMs usually have typical X-ray flat film signs, which appear as isolated or multiple round-like shadows. The shadow diameter is usually in the range of 1-5 cm, the size is different, the density is uniform, the edges are clear, or there are shallow leaves; The thick blood supply artery and drainage vein are connected to the shadow, and the blood supply artery is connected to the hilum, generally 4-7mm in diameter, and occasionally larger than 2cm; the shadow generally does not increase or slowly increases, about 66% of the shadow is located in the lower lung . Under fluoroscopy, the lesions increase during deep inhalation and shrink when exhaling. Based on the above characteristics, most of them can make a clear diagnosis in combination with clinical data. Atypical patients show only large dense images, similar to inflammation, and plain film diagnosis is difficult. Diffuse PAVMS often lacks typical X-ray signs, which can be manifested as diffuse nodules, spotted shadows in the lobe or segment of the lungs, or increased and distorted lung texture. Some plain films are not positive. Therefore, the diagnosis is difficult and further tests are needed.

The sensitivity of echocardiographic acoustic contrast in the diagnosis of clinically significant PAVMs is almost 100%, and even those few non-clinical PAVMs can be found. At the same time, because it is a non-invasive inspection, it is currently widely used. The specific method is as follows: oscillate normal saline or sodium bicarbonate (small bubbles can be generated at this time) from the peripheral vein, and then perform an echocardiogram. Under normal circumstances, small air bubbles will be completely blocked in the pulmonary capillaries and will not enter the left atrium. But when PAVMs were present, air bubbles quickly appeared in the left atrium. Echocardiographic acoustic angiography is very useful for judging extracardiac right-to-left shunts, and can be used to evaluate the efficacy after embolization and to screen family members of patients with HHT. Its disadvantage is that the location and extent of the lesion cannot be determined, and the number of shunts cannot be determined.

Pulmonary perfusion radionuclide scanning is a highly sensitive method for diagnosing PAVMs. It can determine the location and extent of lesions and determine the shunt fraction. The method is as follows: 99mTc-albumin (particle diameter 7-25UM) is injected from the peripheral vein. Under normal circumstances, these particles cannot pass through the pulmonary capillaries. When PAVMs are present, they can pass through the lungs and flow to the brain, kidneys and other organs. Nuclide scans of the lungs and kidneys determine the shunt fraction. Whyte et al. Found that this method has a good correlation with the results of pure oxygen test, and the latter has the following advantages over the latter: no arterial blood sample is needed: it is more suitable for shunt measurement during exercise. The disadvantage is that the shunts in the lungs and the heart cannot be distinguished, the specific anatomical details cannot be observed, and the price is higher.

Spiral CT and electron beam CT (EBCT) are an effective method for the diagnosis of PAVMs. CT performance varies with the type of PAVMS. A single scan or multiple scans with tumor sacs can show round, oval, or lobulated multicystic shadows of medium density, with CT values consistent with those of blood vessels. The obvious one can see the tortuous and dilated blood vessel shadow connected to it. After enhancement, the tumor sac rapidly strengthened, and the peak value was consistent with the right heart-pulmonary artery filling period. The degree of strengthening to the left ventricle decreased. At the same time, it was also observed that the blood supply and drainage of pulmonary arteries and veins, and the "bolus injection" speed-enhanced scanning performed better. Multiple or diffuse PAVMS mainly presents many small nodular reticular structures in the right lower lobe. The angiography shows enhanced and dilated angiograms, but it is difficult to see arterial and venous connectivity. Remy et al. Found that contrast-enhanced EBCT is significantly superior to pulmonary angiography in the correct diagnosis and anatomical display of PAVMs.

3-D spiral CT adopts the surface shadow display method to display the vascular structure from various angles with high accuracy. One study showed that 3-D spiral CT detected PAVMS more than twice as often as pulmonary angiography. The accuracy of 3-D spiral imaging combined with transverse imaging in the diagnosis of PAVMS can reach 95%. However, the indications are selected for surgery or interventional treatment, and the morphological details of this malformation are clear. Multiple or diffuse PAVMs that branch far from the branches of the leaf, segment, and subsegment still require angiography. Recent studies have shown that chest CT is no less sensitive and specific than pulmonary angiography in the diagnosis of pulmonary arteriovenous fistula. With the popularization of 64-slice spiral CT in clinic, its advantages in the diagnosis of PAVMs and possible causes of missed diagnosis have been further studied. Studies by Wang Ke et al. Show that improper application of scanning technology and post-processing technology can also cause The occurrence of misdiagnosis and missed diagnosis.

Magnetic resonance is a non-invasive examination method, which is particularly suitable for those who are contraindicated in using iodine-containing contrast agents and cannot perform enhanced CT examinations. However, due to the influence of air-containing lung tissue, the diagnosis of PAVMs mainly located in the peripheral part of the lung is limited, and individual larger tumor sacs can show cystic structures with no low signal (blood flow effect). Studies have shown that the sensitivity and specificity of spin echo pulse sequences and gradient echo pulse sequences for the diagnosis of PAVMs are not high. Phase contrast movie sequences are the most accurate method for diagnosing PAVMs in nuclear magnetic resonance technology, which can determine the lesion location, morphology, The scope involved. In recent years, the application of enhanced magnetic resonance angiography (CEMRA) has increased the accuracy of diagnosis. It is of great value for observing vascular structures and distinguishing complex and simple types, but it is of limited value in the diagnosis of diffuse types. Khail et al.'S study showed that this method has high sensitivity and specificity for detecting clinically significant PAVMs.

Pulmonary angiography has high temporal and spatial resolution, which can clarify the location, morphology, and extent and extent of PAVMs, especially the sensitivity of 100% when performing superselective angiography. It is still the gold standard for diagnosis of PAVMS.

Imaging methods are classified as selective or non-selective. Selective main pulmonary angiography is usually performed first and the projection is performed in an upright position. The imaging phase includes the entire lung field of both lungs in order to avoid missing lesions. Thereafter, a selective pulmonary angiography was decided as appropriate. The main manifestations of angiography: simple cystic PAVMs can be seen with the filling and development of the pulmonary artery, the drainage pulmonary veins are developed earlier than the normal pulmonary veins, and the supplying artery and the drainage vein are one, and tortuosity and expansion are seen to varying degrees. Larger tumor sacs can be seen with delayed contrast emptying. In complex cystic PAVMs, two or more blood-supplying arteries and draining veins can be seen, the tumor sac can be separated, and the contrast agent emptying is significantly delayed. Diffuse PAVMs are manifested as multiple grape bunch-like small blood pool fillings, and sometimes it is difficult to observe the connection with the branch of pulmonary veins, but DSA or continuous film photography observations show that there is no precapillary stage (substantial filling period) in the corresponding area, or pulmonary veins in the lesion Visualization in advance helps diagnosis.

Digital subtraction angiography has replaced ordinary cardiovascular angiography in the past 10 years, but there is no systematic comparative study on these two technologies. Because angiography is an invasive test, it is mainly used for the diagnosis of PAVMs before treatment and as part of interventional therapy. This method is generally not used during follow-up after treatment.

Recent studies have shown that the combined use of posterior anterior chest radiography and contrast-enhanced ultrasound can obtain 100% sensitivity and negative predictive value. Therefore, a reasonable examination procedure is a combination of contrast ultrasound and posterior anterior chest radiograph. If both are positive, CT examination is feasible. If embolization treatment is available, pulmonary angiography is performed during the treatment. Optimization of thinking procedures.

Traditionally, not all PAVMs require treatment. Only patients with progressively larger lesions, paradoxical embolism, and symptomatic hypoxemia are necessary. However, recent studies have found that many patients with asymptomatic or few lesions can also develop severe neurological complications (such as strokes, brain abscesses, etc.). Therefore, White et al. The symptoms should be treated. The purpose of treatment is to improve the symptoms of hypoxia and prevent the occurrence of severe complications such as stroke, cerebral abscess and hemoptysis. The current methods for treating PAVMs include surgery, transcatheter embolization, and drug treatment. Various methods are summarized as follows:

Surgery is a radical treatment. The surgical indications include: single, isolated PAVMs with symptoms, large shunts, and HHT, with or without complications; multiple PAVMs, with lesions confined to one lobe or one lung; diameter A2. Noise: Apical and L2 can be heard and 3 / 6SM. Blood routine: white blood cells: 2.04 / L, severe anemia.

X: Cystic masses can be seen in the middle lobe and posterior basal segment of the right lung, with smooth edges and multiple leaves, which are closely related to the pulmonary blood vessels, and no consolidation of the remaining lungs is seen. Cardiothoracic ratio: 0.65. Consider multiple pulmonary arteriovenous fistulas. On February 21, 2002, the right lower pulmonary arteriovenous fistula was blocked.

Blocking process: puncture the right femoral vein under local anesthesia, send a 12F delivery sheath into the right lower pulmonary artery trunk, and choose a 30mm diameter ASD occluder made by the domestic Xianjian Company to close the right lower pulmonary artery and the giant tumor sac artery end. Arterial oxygen saturation increased immediately from 65% to 93%. Then performed pulmonary angiography, showing that there was still a branch of the pulmonary artery involved in the anterior segment of the right upper lung, and the tumor sac was visualized. The diameter of the proximal pulmonary artery was about 13 mm. Then a 9F delivery sheath was placed near the branch and the tumor sac was selected. Xianjian's PDA occluder blocked the distal end of the branch, and the oxygen saturation of the femoral artery increased to 97% again. Repeated pulmonary angiography showed no development of the tumor sac. The operation went smoothly, and the patient did not report discomfort, and shared 150ml of iodobile.

SpO2: 65% before occlusion; 97% after occlusion.

Pulmonary artery pressure: before occlusion: 30/10 (18); after occlusion 37/17 (25).

Two Zhang Huan: female, 16 years old, heart murmur from childhood, cyanosis. Pulmonary fistula embolization was performed three times between 1997 and 2002. In January 2002, the right pulmonary artery (right lower pulmonary artery trunk) was blocked with an AGA16 / 14mm occluder, and the blood oxygen saturation was 84%. The symptoms of the onset of chest tightness and shortness of breath have worsened, and he sought treatment again. In April 2004, it was blocked again with AGA26mmASD occluder.

Pulmonary angiography and right pulmonary fistula embolization under local anesthesia. A bilateral right femoral vein puncture was performed, and a 6F sheath was inserted into the right femoral vein. An angiogram showed extensive arteriovenous fistula of the right pulmonary artery. After 6 F pig tail tube angiography was performed through the left femoral vein, a 26 mm ASD occluder was selected. There were no adverse reactions in the test occlusion, and no increase in pulmonary artery pressure.

Pulmonary arterial pressure: first 20/16 (19), post-embolization 35/10 (22)

Pulmonary arterial oxygen: 75.6% before embolization; 90% after embolization.