Contribution to the Morphological Study of the Cerebral Arterial Circle (Circle of Willis) of Rats

Abstract

In this paper the Circle of Willis (CW) was morphologically studied in 87 Wistar rats in the RibeirA£o Preto Medical School. The vessels of the brain were contrasted with colored latex, just after the euthanasia of the animal. After removal of the brain from the skull, the CW and their main components were dissected under microsurgical vision, schematically reproduced and photographed for analysis. The CW presented patterns and variations, which were more or less constant. The constant patterns were: 1. its components have anastomosis among them, making the circle a closed structure; 2. the middle cerebral artery (MCA) and the nasal olfactory artery (NOA) are patent vessels; 3. the origin of the superior cerebellar arteries (SCbAs) ocurred as terminal branches of the basilar artery (BA); and 4. the A2 segment of the anterior cerebral artery (ACA) is an azygos vessel. Among the not constant but frequently observed patterns: 1. the variation in the origin of the posterior cerebral arteries (PCAs), and the presence of the thalamoperforating arteries (TPAs); 2. the presence of the anterior choroidal artery (AChA), and of the corticoamygdaloid artery (CoAmA); 3. the singleness in the origin of the MCAs and of the A1 segments of the ACA; 4. the presence of anastomosis between both A1 segments of the ACAs; 5. the origin of the ventral olfactory artery (VOA) from the A1 segment of the ACA inside the longitudinal cerebral fissure; and 6. the junction of the A1 segments to form an A2 azygos vessel, inside the longitudinal cerebral fissure, near the genu of the corpus callosum. The results of this paper were in accordance with the most part of the data found in the literature, outstanding the finding of well-defined patterns for the anterior and posterior regions of the CW of rats, as well as, the main variations of their components, demonstrated through schemata and photographies.