Endovascular Coil Embolization of Very Small Intracranial Aneurysms Kil Sung Chae, MD1, 2 Pyoung Jeon, MD1 Keon Ha Kim, MD1 Sung Tae Kim, MD1 Hyung Jin Kim, MD1 Hong Sik Byun, MD1 Index terms : Intracranial aneurysm Endovascular treatment Outcome DOI:10.3348/kjr.2010.11.5.536 Korean J Radiol 2010;11:536-541 Received March 23, 2010; accepted after revision June 16, 2010. 1Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea; 2Department of Neurosurgery, Bong Seng Memorial Hospital, Busan 601-723, Korea Corresponding author: Pyoung Jeon, MD, Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-dong, Gangnam-gu, Seoul 135-710, Korea. Tel. (822) 3410-2518 Fax. (822) 3410-2559 e-mail: drpjeon@gmail.com Objective: We aimed to evaluate the results of endovascular coil embolization for very small aneurysms (≤ 3 mm). Materials and Methods: Between March 2005 and December 2008, a total of 31 very small aneurysms in 30 patients were treated by coil embolization. Of the 31 aneurysms, five (16%) were ruptured, as opposed to 26 (84%) that were not. We assessed the procedural complications, immediate angiographic outcome after coiling, clinical outcome, and follow-up MR angiography (MRA). Results: Two thromboembolic complications occurred during the procedure, but did not lead to any persistent neurologic deficit. No procedural aneurysmal rupture was observed and procedure-related morbidity and mortality were both 0%. Occlusion was adequate in 25 aneurysms (81%) and incomplete in six aneurysms (19%). The clinical outcomes of five patients with ruptured aneurysms were good (Glasgow outcome scale ≥ 4), with no bleeding of the treated aneurysms during a mean follow-up period of 13.3 months. On 27 follow-up MRA, there was no recurrence, and the five incompletely occluded aneurysms showed a spontaneous amelioration resulting in an adequate occlusion. Conclusion: Coil embolization of very small aneurysms is technically feasible with good results. The long-term efficacy and the potential as a standard treat- ment strategy remain to be determined by randomized large trials. T he International Subarachnoid Aneurysm Trial acknowledged the greater efficacy of endovascular treatment of ruptured aneurysms compared to clipping. But in this trial, very small aneurysms (≤ 3 mm) were not included, and the conclusion that coiling is the preferred treatment does not apply to these very small aneurysms (1). Endovascular treatment of very small aneurysms is considered to be technically challenging, and high complication rates have been reported (2, 3). The small size of the aneurysmal sac, in these cases, restricts to obtain a stable microcatheter position and coil detachment. As a result, this increases the risk of procedural rupture (2, 4). However, with the advent of more sophisticated endovascular materials, the growing experience of interventionists, and an increased use in adjunctive techniques, such as balloon or stent assisted coiling, several studies have shown that endovascular treatment of very small aneurysms can be done with acceptable risk (2, 3, 5-7). Nonetheless, the efficacy of endovascular treatment in very small aneurysms and the management of unruptured, very small aneurysms are unclear, and remain under continued investigation. Thus, we retrospectively reviewed our consecutive, small series to evaluate the outcome of endovascular coil embolization in very small aneurysms including a large 536 Korean J Radiol 11(5), Sep/Oct 2010