Pipeline Embolization Device with or without Adjunctive Coil Embolization: Analysis of Complications from the IntrePED Registry

Discussion

While the use of adjunctive coil embolization with the PED is not novel, there are questions regarding the efficacy of, and the potential for, increased complications with this strategy compared with PED embolization alone. Certain authors have advocated coil embolization as a method of improving occlusion rates and minimizing the potential for catastrophic aneurysm rupture following the use of flow-diverting stents.^23,25,26 Others have argued that the addition of coil embolization to the procedure yields no significant added advantage in regard to treatment efficacy.²¹ However, our single-center results, which have been previously presented, did identify a statistically significant increase in the need for retreatment with a strategy of PED alone versus PED/coil.²⁷

Additionally, we previously reported our overall (31.7%) and permanent complication (3.2%) rates following use of the PED.¹⁹ However, we did not examine any potential differences in complications between these 2 treatment strategies. In an earlier report on the PED, Siddiqui et al²² described a patient with a giant middle cerebral artery aneurysm treated with 2 PEDs and dense coil embolization. The patient had an acute thrombosis of the PED following the procedure, which was attributed to the dense coil mass. The authors recommended avoiding dense packing of aneurysms when coil embolization is used as an adjunctive treatment with the PED.

In a recent series published by Lin et al,²³ 75 patients treated with the PED alone were compared with 29 patients treated with the PED and adjunctive coil embolization. There was no statistically significant difference in the complication rates between the 2 groups (10.3% with PED/coil versus 8.0% with PED alone, P = .7). Lin et al found, as we did in the IntrePED study, that aneurysms treated with a strategy of PED/coil were statistically larger than aneurysms treated with PED alone (16.3 versus 12.4 mm, P = .02). Nossek et al²⁶ also found similar results in 25 consecutive patients with unruptured aneurysms treated with the PED and adjunctive coiling.

Szikora et al²¹ described their series of 19 patients with wide-neck intracranial aneurysms treated with a strategy of both PED/coil and PED alone. Initially, they treated patients with adjunctive coil embolization, maintaining low coil-packing densities; however, they switched to a strategy of overlapping PEDs without coiling in the latter part of their series. Despite the 2 differing strategies, they had similar occlusion rates at the 6-month follow-up interval. Although their overall complication rate (1 permanent nonrestricting morbidity and 1 mortality) was within the rates published in the literature, they did not specify which treatment strategy was associated with these complications.

In the IntrePED registry, there was a statistically significant difference in the aneurysm size between the 2 cohorts we evaluated (P < .0001). Aneurysms treated with adjunctive coil embolization were larger in both aneurysm size and aneurysm neck size. These differences are likely related to the individual clinician's judgment in regard to the efficacy of stand-alone PED placement for this subset of aneurysms. There may have been a stronger desire to have more immediate contrast stasis during the initial treatment of larger aneurysms due to the higher chance of spontaneous rupture with increasing aneurysm size. In this instance, 2 options for increasing stasis would be to add coil embolization or to place multiple PEDs across the aneurysm neck. Potentially, the use of multiple PEDs may also increase the rate of complications during the procedure. However, we did not identify a difference in the percentage of aneurysms treated with multiple PEDs in either cohort. Patients with larger aneurysms, however, were more likely to have multiple PEDs deployed in both groups (PED alone versus PED/coil).

Another interesting finding in our analysis is the statistically significant difference in the location of aneurysms treated by either strategy. Again, this is likely related to clinical judgment in terms of the aneurysm characteristics and their relationship to the parent vessel. Additionally, endovascular surgeons may be more reluctant to use adjunctive coil embolization when using flow diverters in the posterior cerebral artery/posterior circulation, which is currently an off-label indication in some countries.

While one may presuppose a higher intraprocedural rupture rate with a strategy of PED and adjunctive coils, this was not apparent in our findings. Even with manipulation of the aneurysm wall/dome during coil embolization, there was no statistically significant increased rate of ipsilateral intracranial hemorrhage during or following the procedure. While the anatomical differences between the aneurysms in the 2 cohorts may have certainly influenced the practitioner's judgment as to the optimal treatment strategy, there were no statistically significant differences in the primary or secondary end points for either treatment strategy. Overall, the complication rates reported for the patients in the IntrePED registry for either treatment strategy are in line with those in the published literature for use of flow-diverting stents.¹⁹

Once the decision is made to use adjunctive coil embolization, the setup and performance of the procedure may be distinctly different from those used in deploying a PED alone. First, one must decide whether to coil the aneurysm before or after placement of the flow-diverting stent. One can choose to proceed first with primary or balloon-assisted coil embolization followed by PED deployment. While this strategy would not significantly affect the deployment of the PED from a guide catheter standpoint, it does add the time required to perform the initial embolization to the overall procedure. Once coils are placed within the aneurysm, the microcatheter or balloon microcatheter or both are removed, allowing unencumbered navigation of the catheters for PED deployment. This technique, however, can potentially obscure visualization of the PED during deployment.

Alternatively, one can jail a microcatheter within the aneurysm and initially place the PED followed by aneurysm coiling. This strategy, however, may affect the choice of support catheters. One must ensure that the inner diameter of the guide catheter is sufficiently large enough to support simultaneous navigation of the Marksman catheter (Covidien) and the microcatheter to be used for coil embolization. The use of a second microcatheter for coiling placed through the same guide catheter as the Marksman catheter would likely preclude the use of additional catheters (ie, distal-access catheters) to support PED deployment due to limitations in guide-catheter size. Despite the increase in procedural times and/or case complexity, there was no statistically significant increase in the overall complication rate in terms of neurologic morbidity and mortality in our analysis.