Late recanalization of adequately coiled intracranial aneurysms 117 Introduction Endovascular coiling has become an established treatment for intracranial aneurysms.3,4 A shortcoming of coiling is the possibility of aneurysm recanalization over time due to coil compaction, aneurysm growth, coil migration into intraluminal thrombus or resolution of intraluminal thrombus. Recanalization or reopening occurs in approximately 20% of coiled aneurysms, and about half of these recanalized aneurysms are retreated.5 Currently, it is not known for how long and how frequently coiled aneurysms need to be followed and whether certain subgroups carry a higher risk for late recanalization. Known risk factors for aneurysm recanalization are large aneurysm size and low coil packing density.6,7 Longer passage of time after coiling as a risk factor for recanalization is under debate: some studies have reported more aneurysm recanalization with longer follow-up and therefore prolonged imaging follow- up has been recommended.7,8 However, there is a wide variety in these studies of time intervals between coiling and first follow-up angiography. Recanalization detected on first follow-up angiography some years after coiling, could therefore have developed much earlier. Longer follow-up duration was not associated with more frequent aneurysm recanalization in a systematic review and in studies with fixed follow-up intervals.5,9,10 We determined the incidence of late aneurysm recanalization in 62 patients harboring 71 aneurysms that were treated in the MUMC, with adequate occlusion at 6 months angiographic follow-up. This was a subgroup of a multicenter study (the LOTUS study) which included 400 patients harboring 440 aneurysms. In the LOTUS study possible risk factors for recanalization were also assessed. MaterialsandMethods Patients The Institutional Review Board of the Maastricht University Medical Centre approved the study protocol. Participants provided written informed consent. We retrieved the data from patients with a ruptured or unruptured intracranial aneurysm treated by endovascular coiling between December 1997 and June 2005 and who had adequate aneurysm occlusion - complete aneurysm obliteration or only a small residual aneurysm neck - at 6 months angiographic follow-up according to occlusion status recorded in the databases and radiological reports. Inclusion criteria were: follow-up duration > 4.5 years after coiling, current age between 18 and 70 years, living independently (Glasgow Outcome Scale 4 and 5)11 and no contra-indications for magnetic resonance imaging at 3 Tesla. The upper age limit of 70 years was chosen because it was not considered likely that a patient over 70 years of age would be subjected to retreatment if an aneurysm recanalization were to be found. Firstly there is an increased risk of treatment complications in these patients, and secondly the anticipated annual risk, and thus the lifetime risk of rupture from an aneurysm reopening in these elderly patients is low.12 We contacted the general practitioners of all eligible patients to ascertain whether the patient was still alive. If a patient had died, we retrieved the date and cause of death. The surviving patients received an invitation letter to participate in this long-term magnetic resonance angiography (MRA) follow-up study,
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