Natural History of Intracranial Atherosclerosis

To the Editor: Komotar et al. (4) state that “because the clinical outcome of intracranial atherosclerosis may be vessel-dependent, a thorough review of natural history by vascular territory is most appropriate.” Their main conclusion is that “this critical vessel-by-vessel review of the literature demonstrates that atherosclerosis in different vessels likely represents fundamentally distinct diseases, with overall mortality being substantially lower in cases of middle cerebral artery (MCA) stenosis.” They think this may be explained by the functional anatomy of the brain itself, with the vertebrobasilar vessels supplying critical brainstem structures and the intracranial internal carotid artery (ICA) supplying a larger brain volume that, if infarcted, may generate an overwhelming stroke burden. There is an obvious discrepancy between the general conclusion that MCA atherosclerosis represents a fundamentally distinct disease and the explanation that the reduced overall mortality in such cases is owing to the smaller infarction size or to the fact that the areas involved are less eloquent. No proof that MCA atherosclerosis is fundamentally distinct to the rest of intracranial atherosclerosis is offered in the article. An apparent difference in mortality rates in middle cerebral stenoses is neither scrutinized statistically, nor subjected to meta-analysis or systematic review methodologies. Unfortunately, I could not perform the necessary statistical analysis because the original data are necessary for this purpose. If we accept that this apparent difference in mortality is valid, the offered explanation is not adequate. The great majority of the total mortality of patients with intracranial atherosclerosis is owing to other causes and not to infarcts in the area in which the vessel stenosis can be found. Deaths from infarcts located in the territory of the stenotic intracranial vessel constitute only a small minority of the overall deaths in the published series. Most of these deaths are owing to cardiac causes, and many strokes manifested in territories other than that of the stenotic vessel. If these data prove anything, it is the fact that atherosclerosis is a generalized disease. On the other hand, it is not self-evident that MCA infarcts have a lower mortality than their ICA or vertebrobasilar intracranial counterparts. The variables and the confounding factors are so many that a direct comparison is difficult. Severe MCA infarcts can have a mortality of 17 to 42% (2, 4). These percentages are not less than in cases of ICA (1) or vertebrobasilar (5) infarction. On the other hand, among the many variables that have an impact on stroke prognosis, vessel dependency has not been found to be among them (3, 6, 7). Komotar et al.'s article contains a lot of important information pertaining to different anatomical locations of intracranial atherosclerosis. I think that the location is important mainly for the treatment because it is known that therapeutic interventions in the MCA are more difficult than in the ICA (8). Nikolaus E. Sakellaridis G.