Cerebral Aneurysms Arising at Nonbranching Sites

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Abstract
Background and Purpose The origin and pathogenesis of cerebral aneurysms arising at nonbranching sites are not clear. Using our animal model to induce cerebral aneurysms in rats, we examined induced aneurysms that developed at nonbranching sites. Methods In 35 Sprague-Dawley rats, the left common carotid artery was ligated and renal hypertension was produced to induce cerebral aneurysms. Twelve months later, the circle of Willis was carefully examined under a dissecting microscope. Results Other than cerebral aneurysms at branching sites of the circle of Willis, aneurysmal bulges developing at nonbranching sites were found in the proximal portion of the posterior cerebral artery (P1) on the side of carotid ligation, which supposedly acted as a major collateral pathway after the ligation, in 19 of 35 treated rats. A total of 30 lesions were found in these 19 rats, and they were classified into fusiform aneurysms (22 lesions) involving the entire vessel wall for a short distance and saccular aneurysms (8 le...