Pulmonary arteriovenous malformation (ORPHA:2038)
An aberrant communication between one or more pulmonary arteries and one or more pulmonary veins leading to an anatomic intrapulmonary right-to-left shunt.
Epidemiology
In Japan, prevalence estimated by screening thoracic CT scans is 1/2,600 for all causes of pulmonary arteriovenous malformations (PAVMs).
Clinical description
PAVMs differ from other thoracic vascular anomalies in that the right-to-left shunt places individuals at high risk of paradoxical embolic complications, particularly neurological, and these risks are present whether or not the individual has symptoms from the PAVM(s). In most cases, PAVMs are asymptomatic because of successful physiological compensations such as polycythemia, and higher cardiac outputs. The mean age for presentation is over 50 years of age, though lower if screening programs are utilized. If present, exercise intolerance and dyspnea usually reflect concurrent conditions such as low hemoglobinemia, mild airflow limitation, and/or other cardiorespiratory impairments. Hemoptysis is rare, but is the most frequent cause of maternal death in pregnancy. Major neurological complications such as early onset ischemic strokes, transient ischemic attacks, and cerebral abscesses affect more than 15% of adult patients in recent European studies, but are extremely rare in children. 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). HHT is present in more than 70% of people with PAVMs.
Etiology
The exact pathogenesis is still unknown. As many as 20% of PAVMs are idiopathic (sporadic), although PAVMs generally occur in the context of HHT, or, less frequently, other vascular malformation syndromes. PAVMs can also result from surgical corrections of cyanotic congenital heart disease; gestational trophoblastic disease; the hepatopulmonary syndrome; telomeric disorders, or trauma.
Diagnostic methods
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 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. Complex PAVMs are supplied by more than one pulmonary artery and/or drained by more than one vein; diffuse PAVMs are multiple small PAVMs affecting one or more segments of one or more lobes. Arterial partial pressure of oxygen and oxygen saturation, are often low, and are inversely related to the size of the right-to-left shunt. Approximately one-third of patients demonstrate orthodeoxia, but platypnea is seldom observed.
Differential diagnosis
Differential diagnoses include pulmonary artery aneurysms, pulmonary varices, bronchoceles, systemic artery-pulmonary artery communications and vascular tumors.
Antenatal diagnosis
Prenatal genetic testing is possible for inherited forms of PAVM but is not necessary for proper pregnancy and delivery management.
Genetic counseling
Where PAVMs are multiple and no other precipitants can be identified, the condition is likely inherited, and genetic testing should be suggested. If negative, screening of children for PAVMs is suggested after puberty. Single PAVMs may be due to inherited conditions even in the absence of other symptoms and signs, with mosaic cases described and potentially heritable.
Management and treatment
Treatment of adult patients is recommended irrespective of respiratory symptoms. 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. In highly selected cases, parenchymal sparing surgery may be considered.
Prognosis
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.

                            Last update: 
                            May 2021


                            - Expert reviewer(s): 
                            Dr Ali ALSAFI  - Pr Claire SHOVLIN