Endovascular Coil Embolization of Very Small Intracranial Aneurysms during the procedure in two patients. One was a small thrombus in the parent artery initiating from the aneurys- mal sac and the other was an in-stent thrombosis in the wide-neck aneurysm. Intra-arterial thrombolysis using abciximab (ReoPro ), was successfully performed and the two patients had no permanent neurologic deficits. No procedural aneurysmal ruptures occurred nor procedure- related complications leading to morbidity and mortality. Clinical Outcome Of the 31 aneurysms, a clinical follow-up was available in 30 aneurysms. Two patients who had presented in poor HH grade (IV) and good HH grade (II), respectively, had permanent focal neurologic deficit caused by subarachnoid hemorrhage, but both cases were independent (both, GOS 4) at six months follow-up. The other 27 patients had a good clinical outcome (GOS 5) with no bleeding of coiled aneurysms in all patients during the follow-up period. Follow Up MR Angiographic Results Twenty seven (87%) of 31 aneurysms had follow-up MRA. Of the six incompletely occluded aneurysms on immediate angiography, five were followed. On MRA of these five aneurysms, focal high signal intensities representing remnant arterial flow within the coiled mass were absent or disappeared after serial follow-up (Fig. 1). No other recurrence was seen in the other 22 aneurysms. DISCUSSION In our study, endovascular coil embolization of very small aneurysms was technically feasible and showed successful results without procedural morbidity and mortality, although there were two thromboembolic events during the procedure not resulting neurologic deficits. Coil embolization of very small aneurysms is considered to be technically challenging. Small aneurysms tend to have a thin fragile wall as well as restricted space for insertion of microcatheter and anchoring coils, and have been reported to have higher rates of procedure-related rupture. In a meta-analysis by Brinjikji et al. (8), the incidence of procedural rupture rate among the published studies was 8%. No such procedural ruptures were observed in our series. In most cases, we used the microcatheter that had a shorter distal radiolucent portion over the distal marker and softer microwire (4). We tried a microwire that was never introduced into the aneurysm, and the microcatheter was shaped such that it pointed toward the dome of the aneurysm. The tip of the microcatheter was kept at the neck of the aneurysm as Korean J Radiol 11(5), Sep/Oct 2010 possible, and if necessary, the microcatheter was navigated farther into the aneurysm over the coil loop. The coil insertion was done very slowly, and delicate microcatheter manipulation was used to avoid tension build-up in the aneurysm and simultaneously allow the coil loop to form inside the aneurysm. The high magnification view was useful to observe the movement of coils and microcatheter tip inside the aneurysm. After the end of coil placement, the microcatheter was slowly withdrawn with microwire to minimize the force applied to the coil loops in the aneurysm. Even if minimal contrast filling was seen, no excessive additional coil placement was attempted. A ruptured aneurysm was known as a risk factor for procedure-related rupture (9). Brinjikji et al. (8) confirmed that the incidence of procedural rupture was higher as 10% in ruptured very small aneurysms, compared to 5% in unruptured aneurysms. In the study by van Rooij et al. (5), investigating 47 unruptured and 149 ruptured very small aneurysms, procedural rupture occurred only in ruptured aneurysms. Our series had a large proportion of unruptured aneurysms (84%), unlike most reports which enrolled patients with recently ruptured very small aneurysms. And our results are consistent with previous findings. The most frequent location of very small aneurysms in our study was the internal carotid artery (52%) in the paraclinoid region. In a large, single-center study, the location was significantly more common in the anterior cerebral artery and less common in the internal carotid artery (5). However, it included ruptured aneurysms in 76% of cases and did not demonstrate the data on the basis of ruptured or unruptured aneurysms. Two studies (7, 8), one of which enrolled only unruptured aneurysms, whereas the other demonstrated the data of unruptured aneurysms separately, showed that the location of paracli- noid internal carotid artery was common (41% and 43%, respectively). In addition, all aneurysms with the location of paraclinoidal ICA were unruptured cases in our series. To our knowledge, there was no reference, including a large number of patients where the most frequent location was the ICA of the paraclinoid region in unruptured asymptomatic aneurysms. The Analysis of Treatment by Endovascular approach of Nonruptured Aneurysms (ATENA) study mentioned that the rate of procedural rupture was lower in ICA aneurysms than others (2% in ICA, 2% in anterior cerebral artery/anterior communicat- ing artery, 4% in MCA and 0% in posterior circulation) in the absence of statistical verification (8). Incompletely occluded aneurysms (19%) after coil embolizations were common in our series, which was not the case in previous reports (5% in both van Rooij et al. [5] 539