Objective Wall thickness is a poorly documented characteristic of cerebral aneurysms which may provide insight into adaptive aneurysmal growth, aneurysm rupture risk and response to endovascular treatment. The distribution of aneurysm wall thickness, as observed by intraoperative video microscopy, is described.

Methods 54 unruptured saccular cerebral aneurysms were selected based on the availability of intraoperative video obtained from patients undergoing microsurgical clipping. Aneurysms were assessed for the distribution of wall thickness based on color translucence and quantitation of pixel values at superthin translucent, intermediate and thick regions of the dome. The data were analyzed with respect to aneurysm morphology, location and associated demographic factors.

Results The mean proportions of tissue characteristic among all domes analyzed were found to be 27% superthin, 65% intermediate, and 8% thick. Smaller aneurysms having a maximal dimension D_max <7 mm had a higher proportion of superthin tissue (p=0.003) and lower thick tissue (p=0.001) content. Female gender was associated with a significantly higher proportion of superthin tissue at the aneurysm dome (p=0.038), with no statistical dependence seen with patient age, smoking status or anatomical location.

Conclusion The dome of unruptured aneurysms is a highly heterogeneous region with areas of variable thickness that appear to be intimately related to the process of aneurysm development. This inconstant property affects wall tensile stress, may play a role in aneurysm pathogenesis and focal rupture, and should be incorporated into future analyses of aneurysm rupture risk and mechanics.