Late recanalization of adequately coiled intracranial aneurysms 127 between the aneurysms with a neck remnant (R&R class 2) after coiling or at six months on the one hand, and inadequate occlusion (R&R class 3) at late follow-up on the other, was found (OR 0.45, 95% CI: 0.05-3.79, p=0.46), as these differences in proportion can easily be explained by chance. Table 5. Two by two table comparing occlusion status (R&R class) at six months follow-up with adequacy of occlusion at long term follow-up for 325 patients of the multicenter study.1 Occlusion at long term follow-up Adequate (1 or 2) Inadequate (3) Occlusion at six Complete (1) 232 6 238 months Incomplete (2) 86 1 87 318 7 325 Risk factors for late aneurysm reopening The number of recanalizations in the MUMC cohort was too small to assess risk factors. In the larger LOTUS cohort of 400 patients with 440 aneurysms,1 of which our population was a subgroup, risk factors for late aneurysm recanalization are summarized in Table 2. In uni- and multivariable regression analysis, two factors were identified as both dependent and independent risk factors for late reopening: aneurysm size ш 10 mm (multivariable analysis: OR 4.7, 95% CI: 1.3-16.3, p=0.016) and location on the basilar tip (OR 3.9, 95% CI: 1.1-14.6, p=0.042). Two of the three recanalized aneurysms in our series were at or near the basilar tip (Figure 3 and 4), and one of these was 10 mm in diameter at presentation (Figure 3). Discussion Our study confirms that the great majority of coiled intracranial aneurysms that are adequately occluded at six months follow-up remain adequately occluded, at least during the following five years.1 First appearance of recanalization long after coiling occurred only occasionally and these recanalized aneurysms were not retreated for a variety of reasons. Our results indicate that for coiled aneurysms with adequate occlusion at 6 months, the yield of long-term MRA follow-up is very low. Apart from the risk of aneurysm recanalization, a concern in patients with treated aneurysms is the frequent presence of small untreated aneurysms and the risk to develop de novo aneurysms over time. Imaging follow-up may be indicated to timely detect new aneurysms and growth of untreated additional aneurysms. The results of previous large follow-up studies addressing these issues indicate that in the first five years after coiling (and probably also in the first ten years), both the risk of de novo aneurysm formation and the risk of growth of existing untreated aneurysms is low and the risk of SAH from such aneurysms is extremely low.10,15,16 With such low additional risk of hemorrhage from de novo or untreated additional aneurysms the total risk of late hemorrhage in patients with adequately coiled aneurysms at six months, is expected to be very low. This has been confirmed in previous studies that focused on the recurrent hemorrhage rate in a comparable subgroup of patients with adequately coiled ruptured aneurysms at six months. In those
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