Abstract
Purpose: We review our case series of embolization for unruptured aneurysms <5 mm in maximum diameter to clarify the safety and availability of embolization for these aneurysms, for which surgery is not indicated in the present guidelines.
Materials and methods: The clinical materials were 499 unruptured aneurysms treated with embolization between 2010 and 2016, including 115 very small aneurysms <5 mm in diameter (VS group), 303 sub-small aneurysms 5-10 mm in diameter (SS group), and 81 large aneurysms 10-20 mm in diameter (L group). Profiles of the patients and aneurysms, treatment methods, angiographic and clinical results, and complications were investigated and compared among the 3 different size groups. Giant aneurysms >20 mm in diameter and aneurysms treated with trapping or a flow diverter were excluded because the treatment concept is completely different from that of typical saccular embolization.
Results: No significant difference in patient profile was found. The treatment methods were significantly different among the groups. More than half of the aneurysms in the VS group were treated with a simple method, but most of those in the SS and L groups were treated with various adjunctive techniques. Particularly, the stent-assisted technique was used for 61.7% of the aneurysms in the L group. The angiographic result of embolization was superior in the VS group. Complete occlusion was obtained in 37.4% of the aneurysms in the VS group, 21.1% of the aneurysms in the SS group, and 28.7% of the aneurysms in the L group (p≤0.001). The incidence rate of complications in the VS group was 5.2%, less than that in the other groups, though not significantly. The morbid-mortality rate in the VS group (1.7%) was also similar to or lower than that in the other groups.
Conclusion: Very small aneurysms have been considered untreatable according to a risk-benefit assessment. Some aneurysms have an associated high risk of procedure-related complications because of anatomical difficulty. However, aneurysms that are treatable with a simple method can be embolized more safely than larger aneurysms. Recent improvements in neuroendovascular devices and techniques have led to the expansion of surgical indication to small unruptured aneurysms. For some patients with aneurysms who are very anxious about future ruptures, treatment of their incidental aneurysms may be beneficial to provide them with security. However, the indication should always be decided ensuring safety foremost on the basis of patient consent after an impartial and experience-oriented explanation, considering the small annual rupture rate of very small, unruptured aneurysms.
