An in vitro study to define the term "dense packing" of aneurysms with detachable coils, liquid embolic material and their combination.

SUMMARY: The purpose of this study was to define the terms minimal and maximal "dense packing" of a given cavity with platinum coils and liquid material (cellulose acetate polymer; CAP) using precise in vitro volumetric methods. Tests were performed using a simple in vitro aneurysm model, precisely measured in volume and thereafter filled with platinum coils and/or CAP. The volume of the aneurysmal cavity was measured with a very precise special micropump. The volume of each platinum coil (GDC) was also calculated. Minimal dense packing was defined as the point where there was angiographic evidence of complete filling of the cavity and exclusion from the parent lumen of the aneurysm. Maximal dense packing was defined as the point where introduction of additional coils resulted in their protrusion into the parent artery. At minimal dense packing the ratio of aneurysm volume to coil volume ranged from 25.97% to 32.50%. At maximal dense packing the ratio ranged from 29.55% to 36.16%. The volumetric ratio ofminimal and maximal dense packing obtained was lower than we had expected. The volumetric ratio with CAP was 106.08% and 126.08% and the ratio obtained by the combined use of coils and CAP ranged from 103.78% to 140.2%. When the volumetric ratio of the packing is much lower than the ratio of dense packing by rough estimate, we should expect coil compaction and careful follow-up should be done. Liquid material filled the lumen more densely and the additional use of liquid may be useful to prevent coil compaction.