Outcome of Surgical Clipping of Unruptured Aneurysms as it Compares with a 10-year Nonclipping Survival Period

To the Editor: In their recent article, Krisht et al. (1) compared the outcome of surgical clipping of unruptured aneurysms with a 10-year non-clipping survival period. To accomplish this, they extrapolated the 5-year risk of subarachnoid hemorrhage (SAH), as reported by the International Study on Unruptured Intracranial Aneurysms (ISUIA) (2), to a 10-year period and applied this risk to a group of 116 of their own patients. The authors then compared their results with the estimated morbidity and mortality rates if the aneurysms had been left unclipped. There are two items that deserve attention, one of which bolsters and another that detracts from their conclusions. First, there seems to be a miscalculation in the number of expected bleeds if the aneurysms had been left unclipped. In Figure 3 of the article, the authors have calculated the number of expected bleeds over 5 years for the 7 to 12 mm and large aneurysm groups as 1.2 and 4, respectively. The 5-year ISUIA SAH risk seems to have been applied to the percentage of aneurysms rather than the absolute number. The actual number of expected bleeds should be 2.6% × 70 for aneurysms 7 to 12 mm in diameter and 14.5% × 41 for large aneurysms for an expected bleed rate of 1.8 and 5.9, respectively. The calculation for giant aneurysms is correct. The total number of expected bleeds over 5 years should, therefore, be 12.5 rather than 10. Consequently, the 10-year rupture rate and expected morbidity and mortality rates have been underestimated. On the other hand, although the authors have applied the ISUIA rupture rates to their cohort, they did not evaluate surgical outcome in the same manner. In ISUIA, surgical morbidity was defined as a Rankin score of 3 to 5, a score of less than 24 on the MMSE, or a score of less than 27 on a telephone interview for cognitive status. In the study by Krisht et al., only the Rankin score was recorded. In ISUIA, 4.4% of Group 1 patients (no history of SAH) and 2.4% of Group 2 patients (previous history of SAH) had a Rankin score of 3 to 5. This is comparable to the 3.44% observed by the authors. However, the ISUIA investigators identified an additional 5.5% of Group 1 patients and 7.1% of Group 2 patients who had a poor cognitive status that was not reflected in the Rankin score. Unfortunately, Krisht et al. did not measure the cognitive outcomes in their patients and, as a result, were likely to significantly underestimate the true surgical morbidity in their cohort. Although one could argue that these two items balance to some degree, their very presence raises questions about validity of the study's conclusions. David A. Steven London, Canada

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