This trial is being conducted in order to compare angiographic outcomes in patients receiving 0.014-0.0155" platinum framing and filling coils (larger diameter coils) versus those treated solely with coils less than 0.014" (with a standard diameter).

Hypothesis: Angiographic occlusion at follow-up imaging will be more frequent in patients receiving 0.014-0.0155" platinum coils during embolization compared to those receiving smaller-diameter coils.

Primary Study Objective: Occlusion rate: angiographic occlusion, improvement or no change in the post-coiling appearance of the aneurysm as judged by an independent core lab on follow-up angiography at 12-18 months after endovascular embolization.

Secondary Objectives:

1. Treatment related morbidity and mortality, as measured by the NIH stroke scale.
2. Packing density as measured by volumetric filling of the aneurysm.
3. Clinical outcome at 3-6 and 12-18 months post-coiling, as measured by the modified Rankin scale.
4. Re-hemorrhage and re-treatment rates.

Study Design: FEAT will be a prospective, randomized trial comparing the utilization of 0.014-0.0155" coils versus smaller diameter coils in mid-sized aneurysm treatment. The 0.014-0.0155" bare platinum coils (Stryker, Natick, MA) are FDA-approved and in common use at institutions in this country and across the world. Patients will be enrolled who meet the inclusion criteria and consent to participate. Patients will be randomly assigned by a central web-based system in a 1:1 manner to either the framing coil treatment or the non-framing coil treatment. Data on each patient will be collected at the time of enrollment and treatment, and at first and second follow-up visits.

Inclusion Criteria:

1. Patient presenting with ruptured or unruptured cerebral aneurysm appropriate for endovascular treatment as determined by the neurovascular treating team (neurointerventionist and/or neurosurgeon).
2. The neurointerventionist feels that the aneurysm can be safely treated with either using, or not using, a 0.015-0.0155" platinum coil.
3. Patients are 18-80 years of age (inclusive).
4. Patient must be Hunt and Hess grade 0 to 3.
5. Patient has given fully informed consent to endovascular coiling procedure. If the patient cannot consent for themselves, appropriate written consent has been sought from their next of kin or appropriate power of attorney.
6. Aneurysm 6-14 mm in maximum diameter.
7. Patient is willing and able to return for clinical evaluation and follow-up imaging evaluation (angiography or MRA) at 3-6 months and 12-18 months after endovascular treatment.
8. The patient has not been previously randomized into this trial or another related ongoing trial.
9. The aneurysm has not been previously treated by coiling or clipping.

Exclusion Criteria:

1. Patient has more than one aneurysm requiring treatment in the current treatment session, and only one of those to be treated aneurysms fits the FEAT inclusion criteria (ie - if either (1) a patient has multiple aneurysms, but only one will be treated at enrollment; or (2) if two or more aneurysms are treated during the current treatment session and BOTH are able to be enrolled, then they remain eligible for the trial). Non-treated additional aneurysms may be treated at a later date with any coil type that the operator chooses).
2. Target aneurysm has had previous coil treatment or has been surgically clipped.
3. Hunt and Hess score is 4 or 5 after subarachnoid hemorrhage.
4. Inability to obtain informed consent.
5. Medical or surgical co-morbidity such that the patient's life expectancy is less than 2 years.