Response to Letter by O'Kelly and Macdonald
We appreciate the comments by Drs O'Kelly and Macdonald regarding our article1 and largely agree with them. They raise 2 main points related to censoring at retreatment and to whether degree of aneurysm occlusion should be considered a confounder.
Coil embolization encumbers patients and physicians with follow-up imaging and retreatment to a much greater extent than surgical clipping.2 If one considers this a part of the treatment regimen inherent in coil embolization it is actually not appropriate to censor at retreatment. From the patient’s perspective, when consenting to coil embolization and a real risk of retreatment, the long-term risk of rupture is much more relevant than just the risk of rupture until a possible retreatment. Thus, the primary analysis should be without censoring when evaluating risk of rerupture. In our study, we also censored at retreatment as a sensitivity analysis in order to clarify the risk of rerupture during the time when an aneurysm is incompletely occluded, a major focus of the article.
Degree of aneurysm occlusion should not be considered a confounder, and we appreciate the opportunity to further clarify this important point. Although many prior studies have shown that rates of incomplete aneurysm occlusion are more frequent after coil embolization, our study demonstrates that this is a real liability in terms of the risk of rerupture. Adjusting for degree of occlusion is meant to address the question “Could subtotal aneurysm occlusion explain a trend toward higher rates of rerupture in those treated with coil embolization?” The answer appears to be yes: the absence of an association between coil embolization and risk of rerupture after adjustment for degree of occlusion argues that incomplete occlusion could explain greater rerupture rates after coil embolization. It certainly should never be considered evidence that a difference in rerupture rates between procedure types does not truly exist.
The article is meant to draw attention to the goal of complete occlusion in aneurysm treatment and not to provide evidence that either treatment is superior. Nearly all neurosurgeons have strived for complete occlusion in aneurysm clipping, but there has been debate about its necessity with coil embolization. Our article provides some evidence that attempts to completely occlude aneurysms are justified for both procedures and that they are particularly relevant for coil embolization.
Sources of Funding
The CARAT study was supported by a grant from Boston Scientific.
Johnston SC, Dowd CF, Higashida RT, Lawton MT, Duckwiler GR, Gress DR; CARAT Investigators. Predictors of rehemorrhage after treatment of ruptured intracranial aneurysms: The Cerebral Aneurysm Rerupture After Treatment (CARAT) study. Stroke. 2008; 39: 120–125.
CARAT Investigators. Rates of delayed rebleeding from intracranial aneurysms are low after surgical and endovascular treatment. Stroke. 2006; 37: 1437–1442.