Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The main purpose of this investigation was to characterize the spatial geometry of the fenestrations (windows) in the internal elastic lamina (IEL) from human cerebral arteries. The IEL was isolated from the arterial wall and prepared for examination by the scanning electron microscope. A new method identified a uniform shrinkage for the IEL of only 6.9 (+OR-) 0.21 SEM %. The photomicrographs of the external surface of the IEL revealed a continuous sheet penetrated by numerous round fenestrations with smooth borders. Four geometrical characteristics based upon the diameter and the number of fenestrations in the field of view for every photomicrograph, were calculated for each specimen: Diameter (the average diameter of the fenestrations); Density (the number of fenestrations per square millimeter); Percentage Area (percentage of the surface area comprised of fenestrations); and Ligament Efficiency (minimum width of a solid band of material divided by the centre-to-centre distance for two or a series of adjacent holes). The geometrical characteristics were computed for cylindrical segments of various diameters, associated with the tapering of the arterial tree. A replication of the fenestrations in a photomicrograph and a geometrical model (uniform array of holes with a constant diameter) with an equivalent ligament efficiency, were created in latex sheets for three cylindrical arterial segments with different arterial diameters. The physical behaviour and change in the spatial geometry of the fenestrations were assessed by uniaxially stretching the latex models.;A comparison of the geometrical characteristics for localized groups of fenestrations in the apical region with respect to the circumjacent region to bifurcations (branches in the arterial tree), revealed a significant increase in diameter (7.0 (+OR-) 0.34 SEM (mu)m versus 2.1 (+OR-) 0.13 SEM (mu)m), percentage area (15.0 (+OR-) 1.1 SEM % versus 1.8 (+OR-) 0.2 SEM %) and decrease in ligament efficiency (0.65 (+OR-) 0.08 SEM versus 0.86 (+OR-) 0.006 SEM). The uniaxial tensile characteristics (latex sheets) for replications of the regions of enlarged in relation to normal fenestrations, revealed an increase in elongation of 47 (+OR-) 0.06 SD %. It is proposed that regions of enlarged fenestrations represent a weakness in the IEL which may play a prominent role in the etiology of intracranial saccular aneurysms.



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