Prenatal sonographic detection of basilar aneurysm

Retrospective reviews document the infrequency of intracranial aneurysms in the first decade of life, with an even greater rarity in the first 2 years. Intracranial aneurysms are not known to be associated with trisomy 18. An infant is reported who was diagnosed at 32 weeks gestation as having trisomy 18. Prenatal ultrasonography identified a large cystic lesion in the posterior cerebral circulation. This small-for-gestational-age infant was born at term by dates, but renal maturation suggested a gestational age of 35-36 weeks. He survived 5 days. This is the first report of prenatal sonographic imaging of a basilar artery aneurysm confirmed by autopsy.