Discussion

Previous studies of material cost comparisons between coil embolization and surgical clipping tend to conclude that embolization is the more expensive procedure. Brinjikji et al6 recently reported that not only has the cost of endovascular treatment in both uncomplicated and complicated by major mortality cases been found to be more expensive than their surgical clipping counterparts, but also that coiling costs have grown at a faster rate (4.6% vs 3.6% average annual cost increase between coiling vs clipping, respectively). Hoh et al7 reported similar findings and alluded to equipment material costs as the driver of the cost increase. This likely derives from the fact that to treat an aneurysm, several coils are required, in contrast with a single or a few surgical clips, with the number of coils being the major driver of the cost of this therapy. Indirect costs related to surgery may include longer recovery times and hospital stays but is beyond the scope of this paper. Elucidating the mechanisms influencing final equipment cost will enable operators to control costs without sacrificing clinical outcomes.

Our data show that there is a strong positive linear relationship between coil size and coil cost efficiency, as represented by a value of volume of aneurysm filled per cost. A large component of this relationship is the relatively flat pricing structure for coils of the same line, regardless of size. A very long coil which achieves a larger volume of occlusion may have a relatively similar price to a small coil of the same line which would fill a smaller volume of the aneurysm being treated.

Our analysis demonstrates that the largest determinant of coiling cost efficiency is coil length. Factors such as vendors, coil lines, and frame/fill/finish designation were not found to impact coiling cost efficiency. From this analysis, we conclude that using longer coils with larger volumetric filling, compared with smaller coils with lower volumetric filling, will translate to a lower number of coils required, and subsequently reduced cost per aneurysm treated.

To illustrate the wide variance of size determined cost efficiencies between different coils, it would cost 389 times more to coil a hypothetical 1 cm spherical aneurysm to 30% packing density using the least cost efficient coil (Deltaplush 10, 2 mm×1 cm) compared with the most cost efficient coil (MicroPlex-18 Helical, 10 mm×30 cm) (ratios calculated at available institutional prices with currently available coils at the time of data collection). Even the median cost efficiency coil (Target 360, 4 mm×15 cm) would cost 34.5 times as much as the most volumetrically efficient one. Note that the most important determinate of volumetric efficiency was coil length.

Choice of individual coils during embolization depends on several factors, including the experience of the operator, familiarity with a specific coil line, selection of delivery devices, and peri- and intraprocedural factors. Device cost, and overall procedure cost, should not be obviated when selecting devices, especially in our era of medical care cost containment. Awareness of the vast difference in cost efficiency by coil volume may help operators control cost. However, coil selection should be based on cost only after the safety of using a specific coil is considered, and as part of the overall treatment strategy.

This study did not address intrinsic engineering differences in the coils, including material differences, coil structure design, detachment zone design, or detachment devices. The use of longer coils with a better cost efficiency ratio will fill larger volumes compared with shorter coils, and will translate into a smaller number of devices being implanted. This may also translate into shorter procedural duration with the implications this may represent, including lower radiation doses, shorter requirement of anesthesia, and better time efficiency in the use of angio suites. However, these factors were not evaluated in this study, and may warrant further investigation.

Limitations of our study include the fact that prices reflect only those available to our institution at the time of the analysis. While pricing structures reflect prevailing pricing strategies by vendors, the precise numbers and relationships may vary should pricing strategies change or price negotiations occur. While the cost/volume data are specific to one institution, we have constructed a datasheet for coils available at our institution that allows us to assess price fluctuations in the coils and their cost/volume characteristics. Replacing our institutional pricing values with another would provide easy referencing for coil cost/volume efficiency.

Furthermore, one key assumption made throughout this analysis has been that the required volume of coil implanted is proportional to the volume of the aneurysm. This assumption was based on previous studies that found packing density thresholds to relate to stable occlusion and outcomes.3 However, factors governing stable coil embolization and aneurysm occlusion are not completely understood. Flow diverting devices, such as the pipeline flow diverter stent, have recently shown good outcomes,8 and suggest that packing density may not be the most important endpoint. Other metrics, such as the porosity ratio at the inflow zone of the aneurysm, may prove to be better predictors of outcome and endpoints for therapy. With this alternative treatment paradigm, cost per volume would not be representative. However, in intrasaccular treatment paradigms, packing volume will likely remain one factor among many in predicting treatment stability.

Finally, this approach in the assessment of hybrid coils, such as implants including hydrogels, is limited. Volume of gel coils was assessed to be that at maximum theoretical expansion, which may not be achieved in every case. Furthermore, one of the key potential benefits of hydrogel may relate to biological reactions to the gel9 and may factor into reduced recurrence rates, as seen in the HELPS trial.10