Capillary malformation-arteriovenous malformation syndrome associated with basilar artery aneurysm.

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.