A physical model for the formation of evaginations: a prospective precursor to the creation of saccular aneurysms.

The actual spatial geometry of separate regions of normal and enlarged fenestrations from the internal elastic lamina of human cerebral arteries have been replicated in sheets of latex rubber from scanning electron microscope (SEM) photomicrographs. Geometrical models which assume a constant diameter for the fenestrations, a constant ligament efficiency for the regions of fenestrations and a uniform array of rows and columns have also been created in sheets of latex rubber. The stress (load per unit of cross-sectional area) and strain (percent elongation) were computed for each of the samples during uniaxial stretching. The elongation of the sample representing the region of enlarged fenestrations increased an average of 47% compared to the similar representation of normal fenestrations, at the same increments of stress. This suggests that regions of enlarged fenestrations would form a bulge, indicative of an evagination of the internal elastic lamina. The model configurations demonstrate very similar stress/strain characteristics to the replications. This finding justified the use of the modelling technique using equivalent ligament efficiencies, to represent the actual spatial geometry. During elongation, the average area of the enlarged fenestrations increased at a rate which was an order of magnitude greater than the normal fenestrations. Since a number of observations associated with the development of intracranial saccular aneurysms can be correlated to a region of enlarged fenestrations, the region of enlarged fenestrations may be a defect in the internal elastic lamina which could play a prominent role in the development of intracranial saccular aneurysms.