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Introduction
Pulmonary arteriovenous malformations (PAVMs) are structurally abnormal vascular communications between pulmonary arteries and veins that range in size and complexity and provide an anatomic right-to-left shunt. 1-4 PAVMs allow a proportion of the right ventricular stroke volume to bypass gas exchange, filtration and other functions of the pulmonary capillary bed. Limited prevalence data suggest that PAVMs may affect many as 1 in 2600 individuals (95% CIs 1 in 1315 to 1 in 5555). 5 The majority of PAVMs are due to hereditary haemorrhagic telangiectasia (HHT), 6-9 but there is evidence for underappreciation of both PAVMs 10 and HHT. 11 PAVMs may be present from birth and have usually completed major development by adult life, although they can enlarge later in life, for example, during pregnancy or other alterations in pulmonary haemodynamics. 12 The size of the right-to-left shunt determines the degree of hypoxaemia, 13 14 exuberant ventilation 15 and high cardiac output. 16 PAVMs of any size allow paradoxical emboli that may cause ischaemic strokes, 17 18 myocardial infarction, 18-20 cerebral (brain) 17 21-23 and peripheral abscesses, discitis and migraines. 24-26 Less frequently, PAVMs may cause haemoptysis, haemothorax 27-29 and/or maternal death in pregnancy. 29 Due to compensatory adaptations, respiratory symptoms are frequently absent or not recognised until PAVM treatment has led to improvement or resolution. 1 13-16 26 However, at least one in three patients with PAVMs will have more severe migraines, nosebleeds, respiratory, cardiac or other symptoms than they would if PAVMs were treated. Risk-benefit analyses are almost always in favour of treatment. 30-32 There is evidence for risk reduction for many PAVM complications, 13-17 24 26 29 although contraindications should be considered. Additionally, recent evidence reminds of the potential levels 33 and consequences 1 34 of iatrogenic radiation exposure incurred in delivery of these health benefits.
HHT, the most common cause of PAVMs, is a multisystemic vascular disorder. 6-9 HHT is inherited as an autosomal dominant trait and most commonly results from a pathogenic sequence variant in ENG encoding endoglin (HHT type 1/ HHT1), ACVRL1 encoding ALK-1 (HHT type 2/ HHT2) or SMAD4. 35-37 Frequent nosebleeds are the hallmark of HHT. Approximately 50% of patients with HHT have CT-detectable PAVMs 38 and most have systemic arteriovenous malformations (AVMs) in sites...