What gestational week the circle of Willis ends to develope ?
By the 8th gestational week (52nd embryogenesis day) the mature pattern is complited with the circle of Willis and the capture by the posterior hemispheres of the vertebrobasilar blood supply.
Bilateral narrow vertebral arteries lumens with minimal flow void on T2 images and absent flow on MRA.
Trident sign reflecting persistant trigeminal artery passing through superior aspect of the left Meckel's cave and joining to hypoplastic basilar artery, supplying posterior circulation (nice seen on the coronal images).
Central disc extrusion at C5-C6 segment.