STERICALLY INHOMOGENOUS VISCOELASTIC BEHAVIOR OF HUMAN SACCULAR CEREBRAL ANEURYSMS

To clarify the mechanism leading to the development and rupture of int racranial aneurysms, tensile strength and viscoelastic parameters of 2 2 human saccular aneurysms were investigated. Meridional and circumfer ential strips from the thin and the thick part of the aneurysm sack an d 18 control strips from the basilar artery of 8 patients with patholo gies not affecting the cerebral arterial system were studied. The leng th of the strips was increased in 200-mu m steps, while distending for ce was recorded. Tensile strength and viscoelastic parameters were com puted. In both directions, tensile strength of thick strips was signif icantly lower than that of controls. In the meridional direction, tens ile strength of thin strips was significantly larger than that of thic k ones (14.5 +/- 4.1 x 10(6) vs. 7.5 +/- 2.0 x 10(6) dyn/cm(2), p < 0. 05). In the circumferential direction, thin strips tore at lower strai n values than thick ones (29 +/- 4 vs. 55 +/- 16%, p < 0.05). Viscoela stic parameters changed in parallel. In circumferential direction, val ues of thick and thin strips were significantly lower than those of co ntrols. In the meridional direction, values of thin strips were signif icantly higher than those of the thick ones. These observations show t hat characteristic mechanical deterioration and steric inhomogeneities accompany the loss of smooth muscle cells and the derangement of conn ective tissue elements in the wall of intracranial aneurysms, which ma y explain certain steps in their initiation, enlargement and rupture.