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Purpose: The presence of a pulmonary arteriovenous malformation (PAVM) causes a permanent right-to-left shunt (RLS). A pulmonary RLS carries the risk of paradoxical embolisation by bypassing the capillary filtering network and is an important cause of neurological complications in patients with hereditary hemorrhagic telangiectasia (HHT). A pulmonary RLS can be diagnosed and graded by transthoracic contrast echocardiography (TTCE). The present study evaluated whether the grade of pulmonary RLS measured on TTCE isassociated with the prevalence of neurological complications in persons screened for HHT.Methods: Between May 2004 and March 2011 we used TTCE as screening for PAVMs in HHT-suspected persons. Pulmonary RLS on TTCE was graded as none, minimal, moderate, or large. All neurological events were diagnosed by neurologists and confirmed by appropriate imaging techniques.Results: A sufficient TTCE was performed in 678 out of 723 persons screened for HHT. In 616 persons a definite presence (n=389) or absence(n=227) of HHT could be diagnosed and were included. TTCE revealed a pulmonary RLS in 266 (43.2%) persons (mean age 42±15 yrs, 64.7% female, 36% minimal, 22% moderate, 42% large RLS). Within all screened persons, the prevalence of ischemic stroke was 2.5%, TIA 1.4%, brain abscess 0.5%, overall migraine 15.4% and migraine with aura (MA+) 7.9%. The prevalence of cerebral ischemic stroke and MA+ was only significantly increased in case of a large pulmonary RLS on TTCE (0.6%, 1.1%, 1.8% and 12.7% for no, small, moderate or large RLS in ischemic stroke, and 5.1%, 4.9%, 7.7% or 27.5% for no, small, moderate or large RLS in MA+, p<0.001). There was no significant difference in the prevalence of TIA, brain abscess or overall migraine in the different RLS grades.Conclusion: In persons screened for HHT, the prevalence of ischemic stroke and migraine with aura is increased only in the presence of a large right-to-left shunt on transthoracic contrastechocardiography.