Introduction Very small aneurysms (<3 mm) have a low rate of spontaneous rupture, however when treatment is warranted, pose an increased risk of procedural complications, specifically intraprocedural rupture. Endovascular treatment of these aneurysms is controversial given the high complication rate, particularly intraprocedural rupture. However, there are patients who are better suited to endovascular occlusion due to clinical grade or comorbidities. We analyzed this series of patients to evaluate procedure safety and acute outcomes using this newer coil technology.

Methods The MUSC endovascular registry is a prospective database with predefined parameters which tracks all diagnostic and endovascular interventions. A database query was performed to obtain all aneurysms measuring <3 mm. Immediate occlusion rates and procedural complications were evaluated for safety and efficacy. The most current clinical status of patients was also evaluated for outcome analysis.

Results 15 patients with 16 aneurysms underwent coil embolization between August 2009 and February 2010, representing 17.2% of all aneurysms coiled during that period. 11 of the 16 aneurysms (69%) were ruptured, four (25%) were unruptured aneurysms in patients with a history of subarachnoid hemorrhage (SAH) and a previously treated ruptured aneurysm and one patient was unruptured with a strong family history of SAH. Mean length of the largest diameter was 2.7 mm (range 2–3 mm). All but one aneurysm achieved complete occlusion acutely, and high packing densities were obtained in all aneurysms. Eight aneurysms (seven ruptured) were treated with a balloon assist technique and were not associated with any adverse events. Four aneurysms (one ruptured) were stent assisted, with two of the procedures (both unruptured) were complicated by intraprocedural rupture. Both patients were discharged from the hospital within 4 days of the procedure with no clinical deficits and a modified Rankin scale (mRS) score of 0. Four aneurysms (three ruptured) were treated without adjunctive devices and one patient (ruptured) had an intraprocedural rupture without clinical consequence and was discharge on hospital day 14. Overall, 12 patients had an mRS score of 0 and one patient a score of 1. One patient has an mRS score of 4 but presented with a Hunt and Hess score of 5 with minimal improvement. One patient is currently completing his acute treatment.

Conclusions Very small aneurysms account for a significant number of aneurysms treated at our institution. Complete occlusion is achievable in a large percentage of these aneurysms but they are associated with a higher procedural complication rate. In patients with ruptured (and unruptured) aneurysms, clinical outcomes were very good. Long term outcomes and follow-up are forthcoming.