ABSTRACT This study demonstrated that distal branches of the anterior
cerebral artery (ACA) are joined by interarterial anastomoses to rami of the middle
cerebral artery (MCA) in the normal Wistar rat. Arteries of 36- and 56-day-old
animals were dilated with papaverine and injected with Vultex. Vultex arrived at
corresponding ACA and MCA collaterals simultaneously as determined by microscopy
through a skull window and photography. There were about 29 ACAMCA
junctions per hemisphere. Junction density was nearly constant along the
frontal-occipital axis. The anastomoses were most numerous between 2 and 3 mm
lateral to the midline and were less than 120 pm in internal diameter. No significant
difference was found between total numbers of junctions for right versus left
hemispheres or between age groups. The most evident collateral pattern was characterized
by two ACA end rami joining two MCA end branches to form a closed,
diamond-shaped collateral unit. Considerations were given to alternate routes of
blood flow into the MCA tissue field. We conclude abundant dorsal anastomoses
exist in 36- and 56-day-old rats and are the prime potential source for ACA collateral
supply to the MCA tissue field.