Experimental Carotid Ligation Followed by Aneurysmal Formation and Other Morphological Changes in the Circle of Willis

T HE circle of Wil l is is of cons iderab le impor t ance in ensur ing a cont inuous blood supp ly to the bra in . I n a y o u n g person wi th a wel l -deve loped circle of Will is , no serious effects follow the occlusion of one of the caro t id or ve r t eb ra l ar ter ies , b u t in old people a t h r o m b o t i c or embol ic occlusion of a ca ro t id a r t e r y is a ve ry common cause of ce rebrovascu la r incidence. 4,~,~,~5 The shape of the circle of Will is in the newborn is differen t f rom t h a t in the adul t . Thus the pos te r ior communica t i ng ar ter ies , and also those por t ions of the an te r io r cerebra l a r te r ies belonging to the circle of Will is , are r e l a t ive ly nar rower in the l a t t e r f ,~3 and this m a y be a c o n t r i b u t o r y fac tor in the d e v e l o p m e n t of i n t r ace reb ra l vascu la r lesions. ~~