Important note: This background is “as is” from the First HHT Guidelines. To access references or the complete manuscript, refer to the First Guidelines.

PAVMs are present in 15-50% of people with HHT and have been associated with life-threatening complications, as previously reviewed (81-82).  The rationale for screening HHT patients for PAVMs is that screening will detect a treatable PAVM before the development of a life-threatening or debilitating complication. We therefore reviewed the evidence regarding complications of PAVMs, the performance of screening tests, and the effectiveness of treatment for PAVMs. 

PAVMs have been shown to be associated with disabling and life-threatening complications, such as stroke, transient ischaemic attack (TIA), cerebral abscess, massive haemoptysis and spontaneous haemothorax (81, 83-86) in retrospective series. The neurological complications are presumed to occur via paradoxical embolisation through PAVMs, whereas the haemorrhagic complications occur due to spontaneous PAVM rupture. These complications have been demonstrated in largely adult series of HHT patients, although they have also been demonstrated in a paediatric HHT series (87), albeit smaller in size. There have also been small series reporting these same complications during pregnancy (88, 89) and the expert panel agreed that the complication risk appears to be greater during pregnancy. 

Since clinical symptoms and signs of PAVMs are often absent before the development of complications, a number of screening tests have been studied,including physiological methods of measurement of intrapulmonary shunt as well as multiple different imaging modalities. In the one comparative study (table 3), transthoracic contrast echocardiography with agitated saline (TTCE) has been demonstrated to have the best combination of high sensitivity (82) and low risk (90, 91) among screening tests for PAVMs in adults with HHT, when compared with the reference standard tests (CT and pulmonary angiography). There have been no comparative screening studies for PAVMs in children with HHT. 

Embolisation has been shown in several non-controlled series (83, 85, 92-96) to be efficacious and to have a good safety profile, with only rare PAVM-related complications during 5-10 year follow-up (table 4) . In the short term, these studies showed very high rates of immediate technical success and significant improvement in oxygenation (table 4). Longer term after embolisation, reperfusion did occur in up to 15%, and growth of small PAVMs in up to 18% (table 4), but clinical complications were very rare. These series primarily reported outcomes for treatment of PAVMs with feeding artery diameter of 3 mm or greater, although expert experience suggests that embolisation of smaller PAVMs(2-3 mm) has similar outcomes. The safety and efficacy were similar for large PAVMs in adults (97) as well as for PAVMs in children (87), although there is little experience with embolisation of PAVMs in children under the age of 4 years. There is only one small case series of embolisation during pregnancy (98) suggesting reasonable safety. Although there is no evidence regarding differences in outcomes according to expertise embolisation of PAVMs,the expert panel agreed that centres with experience in this procedure are more likely to have better outcomes than inexperienced centres. 

The long-term follow-up of PAVMs is described using the thorax. This allows detection of reperfusion by non-involution of the aneurysmal ~1 year after embolisation and also detection of growth of small residual PAVMs,which are common in HHT (85) TTCE has been shown to be not useful after embolisation, given that it remains positive in ~90% of patients after embolisation (99). 

Important note: This background is “as is” from the First International HHT Guidelines. To access references or the complete manuscript, refer to the First Guidelines.