Circle of Willis abnormalities and their clinical importance in ageing brains: A cadaveric anatomical and pathological study

Abstract

The circle of Willis (CW) located at the base of the brain forms an important collateral network to maintain adequate cerebral perfusion, especially in clinical situations requiring compensatory changes in blood flow. Morphopathological changes in the CW may relate to the severity of the symptoms of certain neurodegenerative and cerebrovascular disorders. The purpose of this study was to investigate the CW abnormalities and their clinical importance in ageing brains. The CW was examined macroscopically in 73 formalin-fixed samples to determine the degree of stenosis of each CW component, atherosclerosis of the CW, hypoplasia (threshold diameter < 1 mm), anatomical variations and aneurysms. Age-related neurodegenerative and cerebrovascular pathologies were screened using immunohistopathological techniques on specific neuroanatomical regions based on standard guidelines. The majority of the elderly brains -93 % (68/73) presented at least a single hypoplastic CW component at death. Anatomical variations were mostly identified in communicating arteries, followed by proximal posterior and anterior cerebral arteries. Arterial bifurcations were found to be the predominant sites for cerebral aneurysms. More than 90 % of the elderly brains presented CW atherosclerosis at death. CW abnormalities did not show any strong associations with neurodegenerative pathologies except for an "at risk" significant association observed between Braak's neurofibrillary tangle (NFT) stages 1-VI and CW atherosclerosis grades ≥ mild (p = 0.05). However, a significant association was observed between microscopic infarcts in deep white matter and hypoplasia in communicating arteries with Fisher's exact test (p < 0.05). Overall, CW abnormalities were predominant in the ageing brains, however their relationships to the occurrence and severity of the symptoms of neurodegenerative pathologies were found to be low.

Keywords: Ageing brains; Anatomical variations; Circle of Willis atherosclerosis; Microscopic infarcts; Neurodegenerative pathologies; Vascular genetic risk factors.