Coil packing density

Packing density is calculated as the total volume of coils deployed (from each coil's length and diameter) divided by the aneurysm's volume, times 100. Even a well-packed aneurysm is mostly blood and thrombus: typical values are in the 20 to 35% range.

Early clinical studies found that aneurysms packed above roughly 20 to 25% were less likely to compact and recanalize, which made packing density one of the few treatment variables an operator can directly influence. The effect is not linear, and very large aneurysms may be impossible to pack densely enough to reach a low risk.

Accurate packing density depends on an accurate aneurysm volume, which is usually estimated from 3D angiography. Small errors in measuring a large aneurysm can shift the calculated density by several percentage points.