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Pulmonary arteriovenous malformation
Pulmonary arteriovenous malformation (PAVM) describes an anatomic communication between a pulmonary artery and a pulmonary vein leading to a right to left extracardiac shunt that can be asymptomatic or can lead to varying manifestations such as dyspnea, hemoptysis, and neurological symptoms.
Prevalence is estimated at around 1/ 2,600. There is a minor female predominance.
Clinical features vary widely but in most cases, PAVMs are asymptomatic because of successful physiological compensations (i.e. polycythemia, high cardiac output). The mean age for presentation is over 50ys of age, though lower if screening programs are utilized. Dyspnea, fatigue and exercise intolerance are more common in patients with concurrent conditions such as anemia, cardiac and/or respiratory diseases. Hemoptysis is rare, but is the most frequent cause of maternal death in pregnancy. Neurological manifestations including migraines, ischemic strokes/ transient ischemic attacks, and cerebral abscesses are attributed to paradoxical embolism through PAVMs. Tachyarrhythmias and angina may be present at diagnosis, although they usually reflect a more complex underlying pathology; particularly iron deficiency and/or visceral arteriovenous malformations (AVMs) due to underlying hereditary hemorrhagic telangiectasia (HHT; see this term). HHT is present in the majority of recognized cases of PAVMs (>90% in some series).
The exact pathogenesis is still unknown. Although generally observed in the context of HHT, PAVMs may also be idiopathic. Much rarer etiological causes include cavopulmonary surgical corrections of cyanotic congenital heart disease; gestational trophoblastic disease; and arteriovenous fistulae induced by trauma.
Diagnosis is based on imaging demonstrating one or more AVMs usually located in the lower lobes of the lungs. Although PAVMs may be clearly visible on chest x-rays, many are not, even when clinically significant. Computed tomography (CT) is generally considered the gold-standard investigation for diagnosing PAVMs. AVMs can be isolated or multiple, unilateral or bilateral. 'Simple' lesions consist of an aneurysmal venous sac communicating with a dilated feeding artery and draining vein. Other PAVMs are complex plexiform masses with multiple afferent and efferent vessels. Diffuse PAVMs are multiple small PAVMs affecting a single segment, or every segment of one or more lobes. Arterial partial pressure of oxygen (PaO2) and oxygen saturation (SaO2), are often low, and are inversely related to the size of the right to left shunt. Approximately 1/3 of patients demonstrate orthodeoxia, but platypnea is seldom observed.
Differential diagnoses include pulmonary artery aneurysms, pulmonary varices, bronchoceles and vascular tumors.
Genetic counseling focuses on the presence of hereditary haemorrhagic telangiectasia (HHT). Since HHT can be difficult to diagnose, and familial PAVMs are recognized in non-HHT families, screening of first degree relatives is common.
Management and treatment
Percutaneous transcatheter embolization of the pulmonary artery/ies feeding the PAVMs is the treatment of choice, irrespective of respiratory symptoms. Additional recommendations include judicious dental hygiene; antibiotic prophylaxis prior to dental and surgical procedures; optimization of iron status; and pregnancy-specific recommendations.
With appropriate management and interventions, prognosis is generally very good with many patients reaching their 9th and 10th decades of life. During pregnancy, however, there is a 1% maternal death rate. Difficult management issues arise in patients who continue to experience neurological complications, or when PAVMs acquire a systemic arterial supply, increasing the risk of hemoptysis.