intracranial aneurysm
description
intracranial aneurysms are rarely seen prenatally. the primary defect is probably a developmental deficiency of the medial layer of the arterial wall leading to localised aneurysmal dilatation. aneurysms are more peripherally sited in a paediatric population. in the only prenatal report, the aneurysm arose from the termination of the basilar artery.
diagnosis
there has only been one report of an intracranial aneurysm detected prenatally, and this was a retrospective diagnosis. the aneurysm presented as a 2 cm smooth echo free mass ventral to the brainstem. doppler was not performed, but one would have expected an arterial signal with no venous characteristics which would therefore distinguish it from an arteriovenous malformation.the fetus was also growth restricted and had features of aneuploidy, and karyotyping confirmed the diagnosis of trisomy 18.
differential diagnosis
other causes of solitary intracranial cysts need exclusion, such as porencephaly, arachnoid cysts, cysts of the cavum septi pellucidi et vergae, dandy-walker malformation, the dorsal cyst of holoprosencephaly, dilatation of the third ventricle (secondary to aqueductal stenosis or agenesis of the corpus callosum). in the presence of demonstrable flow within the cyst the only diagnosis requiring exclusion is arteriovenous malformation, which although commonly affecting the vein of galen in a midline site, can be asymmetrically located. the lack of a venous component in the flow velocity waveform will enable the correct diagnosis is to be made.
sonographic features
echolucent intracranial cyst.
arterial signal on doppler interrogation.
associated syndromes
references
muszynski ca, carpenter rj, armstrong dl prenatal sonographic detection of basilar aneurysm pediatr neurol 10: 70-72