Endovascular Treatment of Very Small Intracranial Aneurysms: Meta-Analysis

BACKGROUND AND PURPOSE:Outcomes of endovascular treatment of very small intracranial aneurysms are still not well-characterized. Recently, several series assessing coil embolization of tiny aneurysms have presented new promising results. Thus, we performed a systematic review and meta-analysis of studies evaluating endovascular treatment of very small intracranial aneurysms.MATERIALS AND METHODS:We conducted a computerized search of Scopus, Medline, and the Web of Science for studies on endovascular treatment of very small (≤3 mm in diameter) intracranial aneurysms published between January 1996 and May 2015. Using a random-effects model, we evaluated clinical and angiographic outcomes.RESULTS:Twenty-two studies with 1105 tiny aneurysms (844 ruptured and 261 unruptured) endovascularly treated were included. Postoperative and long-term complete occlusion was achieved in 85% (95% CI, 78%–90%) and 91% (95% CI, 87%–94%) of aneurysms, respectively. The recanalization rate was 6% (95% CI, 4%–11%) and retreatment occurred in 7% (95% CI, 5%–9%) of cases. Seventy-nine percent (95% CI, 64%–89%) of patients had good neurologic outcome at long-term follow-up. Intraprocedural rupture occurred in 7% (95% CI, 5%–9%) of the coiling procedures, while thromboembolic complications occurred in 4% (95% CI, 3%–6%).CONCLUSIONS:Coil embolization of very small intracranial aneurysms can be performed safely and effectively. In the case of unruptured aneurysms, procedure-related complications are not negligible. Patients and providers should consider such risks when engaged in a shared decision-making process.

Endovascular treatment is now the standard of care for most intracranial aneurysms (IAs).^1,2 Despite endovascular treatment being safe with low morbidity and mortality rates, in certain groups of aneurysms, a detailed risk-benefit assessment of this treatment must be considered.³ Coil embolization of very small IAs (≤3 mm) is particularly challenging due to the thin fragile wall of small IAs, with limited space to obtain a stable microcatheter position for coil deployment.^4–6 In the Barrow Ruptured Aneurysm Trial, very small aneurysm size was one of the main reasons for the high crossover rate from the coiling to the clipping group.² A previous meta-analysis that included only 7 studies observed a relatively high complication rate, especially in terms of periprocedural rupture risk.⁷ Since then, several technologic improvements, including better microcatheters and steerable soft microguidewires, compliant and easier-to-navigate balloons, and the availability of newer distal access catheters and very small endovascular coils have been developed, which may have enhanced our ability in coiling very small aneurysms. Since publication of the previous meta-analysis, many recent series have outlined results and complications in this specific subset of aneurysms.In an attempt to examine the current safety and efficacy of endovascular treatment of tiny intracranial aneurysms, we performed an updated systematic review and meta-analysis of the literature addressing the endovascular treatment of very small intracranial aneurysms. We also compared results from studies included in a previously published meta-analysis from 2010⁷ with more recently published studies to determine whether there have been improvements in outcomes with time. We hypothesized that recently published studies would demonstrate lower intraoperative rupture rates and higher rates of aneurysm occlusion.