Age changes at cerebral artery bifurcations and the pathogenesis of berry aneurysms.

Cerebral artery bifurcations with and without aneurysms were studied in postmortem brains by histology (1-micron resin sections) and by scanning electron microscopy. Specimens were taken from 20 patients without aneurysms with an age range of 1 month--80 years. Gaps in the tunica media at the carina and the lateral wall of the bifurcations were observed in 60% of specimens from arteries at all ages, but they were larger in older patients. A more striking change with age was the development of inelastic pads of intimal thickening in relation to bifurcations. Intimal pads were observed at and distal to the carina of bifurcations, but scanning electron microscopy also revealed intimal pads proximal to bifurcations in 60% of patients over the age of 30 years and in 2 out of 9 (22%) patients under 10 years. Similar pads covered a much wider area of vessel wall proximal to the necks of berry aneurysms in the 15 patients studied. Contralateral bifuractions in these patients showed no difference from non-aneurysm patients. It is suggested that the inelastic intimal pads form as a result of haemodynamic stress and that the presence of such pads may alter the stresses and strains at vessel bifurcations. Together with the presence of a gap in the tunica media, the pattern of inelastic intimal pad formation may be a major predisposing factor in the formation of cerebral artery aneurysms.