Unruptured Intracranial Aneurysms

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Abstract
The conclusions reached by Wiebers et al. (Dec. 10 issue)1 about the natural history of aneurysmal subarachnoid hemorrhage arouse concern because of the inhomogeneous grouping of patients and the differences in the rates of subarachnoid hemorrhage at different sites. Since they included intracavernous aneurysms in their determination of rupture rates, the rates for aneurysms truly within the subarachnoid space may be underestimated, since intracavernous aneurysms rarely cause subarachnoid hemorrhage.2 To a lesser extent, the same caveat may apply to proximal infraclinoid ophthalmic aneurysms and those arising from the clinoidal segment of the carotid artery, since they are often protected by dura and bone. The grouping of aneurysms in these locations with aneurysms that are free within the subarachnoid space combines categories of aneurysms that entail very different risks of hemorrhage. Of the 1937 aneurysms, 669 (34.5 percent) were in these proximal locations, a point that may have important implications for the overall findings ( Table 1 ).