**5. Role of direct surgery for recurrent aneurysms after endovascular coil embolization**

The treatment selection for recurrent cerebral aneurysms after endovascular treatment should be based on an individualization policy. However, the difficulty of direct surgery is high in these aneurysms because of coil mass extrusion, thrombus formation in the aneurysms, adhesion to vital cranial nerves and branches due to inflammatory changes in the aneurysm wall, thickening of the aneurysm wall, and coil loop scarring to the parent artery. On the other hand, endovascular treatment is often relatively easy to retreat. Therefore, endovascular retreatment is the first choice to treat recurrent cerebral aneurysms after endovascular treatment safely.

Is endovascular treatment the optimal retreatment strategy for all patients with recurrent cerebral aneurysms after endovascular treatment? The recurrence rate of

#### *Perspective Chapter: Role of Direct Surgery for Recurrent Aneurysms after Endovascular Treatment DOI: http://dx.doi.org/10.5772/intechopen.112076*

cerebral aneurysms after initial endovascular treatment has been reported to range from 4.7 to 17.4% [30–32]. On the other hand, the re-recurrence rate of endovascular retreated recurrent aneurysms has been reported to have a high cerebral aneurysm recurrence rate ranging from 44.1 to 48.8% [32–34]. Therefore, if endovascular retreatment is chosen for all post-endovascular recurrent cerebral aneurysms, the reoccurrence rate will inevitably be high, and multiple retreatments may sometimes be required. Although endovascular retreatment is a relatively safe and easy treatment for recurrent cerebral aneurysms after initial endovascular treatment, we should be careful not to choose this treatment method too easily.

It has been reported that the recurrence rate of endovascular treatment of recurrent cerebral aneurysms after initial endovascular treatment varies greatly depending on the mechanisms of recurrence (**Figure 2**). When endovascular treatment was selected for recurrent cerebral aneurysms after initial endovascular treatment, the multiple re-coiling rates for patients with recurrence by the coil compaction mechanism was 21.3%. The multiple re-coiling rates for patients with recurrence by the regrowth mechanism were extremely high at 85.7% [29]. Therefore, choosing direct surgery for recurrent cerebral aneurysms with a regrowth mechanism is crucial to minimize the multiple recurrences.

In addition, the flow diverter is now available as a new option for treating recurrent cerebral aneurysms after initial coil embolization. In a study comparing the pipeline embolization device (PED: 18 patients) and coil embolization for recurrent aneurysms after initial coil embolization, the complication rate was similar for PED and coil embolization, and the recurrence rate was significantly lower for PED than for coil embolization (p < 0.037) [35]. Moreover, in a study of flow diverter treatment (17 patients) for

*(a)-(d): Schema of the mechanisms of the recurrence. (a): Complete obliteration of the aneurysm. (b): Coil compaction. (c): Aneurysm regrowth. (d): Fundal migration.*

recurrent aneurysms after initial coil embolization with the stent, all patients had good outcomes (mRS 0-2), 16 patients had complete aneurysm occlusion, and one patient tended aneurysm regrowth [36]. Thus, the flow diverter, a novel treatment method, is currently a promising treatment option for recurrent cerebral aneurysms after initial coil embolization. Future case series and long-term follow-up studies are warranted.

In deciding the optimal treatment for patients with recurrent cerebral aneurysms after initial coil embolization, it is critical to consider the presence or absence of systemic complications comprehensively, the site of the aneurysms, and the mechanism of aneurysm recurrence in each case to determine the optimal treatment strategy.
