Capillary malformation‐arteriovenous malformation syndrome associated with basilar artery aneurysm

Abstract A 23‐day‐old boy with prenatal diagnosis of basilar artery aneurysm presented with multiple congenital red patches consistent with capillary malformations. Genetic testing confirmed the presence of a heterozygous pathogenic variant of the RASA1 gene, confirming the diagnosis of capillary malformation‐arteriovenous malformation (CM‐AVM) syndrome. This case illustrates an atypical presentation of the RASA1 associated CM‐AVM syndrome, with the intracranial vascular malformation diagnosis preceding the identification of the skin lesions. Arterial aneurysms have been associated with CM‐AVM syndrome in rare instances but to our knowledge this is the first reported case of an aneurysm of the basilar artery.