ASSESSMENT OF THE NORMAL FETAL CIRCLE OF WILLIS BY 3D ULTRASOUND IN THE 2ND AND 3RD TRIMESTER

Frances Miceli, RDMS, RDCS, Senior Sonographer Christopher Kohlenberg Department of Perinatal Ultrasound, Nepean Hospital, Penrith, NSW

Abstract
Located on the floor of the cranial cavity the Circle of Willis surrounds the pituitary fossa and the optic chiasma. Its branches supply the developing fetal brain. These vessels and the associated cerebral tissue have been studied extensively by two-dimensional (2D) ultrasound and conventional colour and spectral Doppler flows.

Three-dimensional (3D) ultrasound is a new modality that is able to define clearly the relative anatomy of all the major cerebral vessels and surrounding cerebrum. This is made possible by the ability of 3D ultrasound to capture, store, render and rotate an image. By power Doppler assessment of the cerebral vasculature this study examined the potential use of 3D ultrasound to assess the vessels of the normal fetal Circle of Willis and the surrounding cerebrum. The exam was successful in 90% of fetuses between 18-30 weeks gestation. In approximately 6.6% of cases the Circle of Willis was not able to be visualized due to maternal body habitus and in the remaining 3.3% of cases fetal head position prevented an adequate image after several attempts had been made.

The clinical use of 3D ultrasound is a new field. It is likely that its application will greatly add to the earlier detection and diagnosis of many congenital abnormalities such as congenital aneurysms, intracranial tumours and haemorrhages, lobar holoprosencephaly, lissencephaly, AV malformations and other fetal cranial abnormalities.

Citation
Micelli F. Assessment of the normal fetal Circle of Willis by 3D ultrasound in the 2nd and 3rd trimester. ASUM Bulletin 2001.1:18-20

Keywords
obstetric, fetal ultrasound, Circle of Willis, second trimester, third trimester, 3D ultrasound