Comparative morphological variations and abnormalities of circles of Willis: a minireview including two personal cases.

Two rare cases of the circle of Willis are presented. One of them represents a fetal circle of Willis (crown-rump length, or CRL, 17 cm), the other one is adult circle from a male cadaver 65 years of age. Arterial variations and abnormalities of the represented circles of Willis are described. Interpretation of the appearance of variations and abnormalities is based on the acceptable embryological, anatomical, and clinical reports. Summarizing these opinions, we have supplemented them with a hypothesis that arterial variations and abnormalities could preserve their relationships because of constant interaction between primitive arterial remnants and cerebral arteries in postnatal life, unless some pathological lesions appear.