**3.6 Flow diversion**

This method was developed in the 2000s. The concept of Flow Diversion is that a high-mesh density stent placed in the parent artery will disrupts blood flow into the aneurysm with the subsequent thrombosis of the aneurysm, this process takes 6 weeks to 6 months in average in radiographic follow-ups. Moreover, the stent in parent artery provides a scaffold for which endothelium can grow [62]. In 2011, the FDA approved the Pipeline Embolization Device (PED) for large or giant (≥10 mm) wide-necked intracranial aneurysms from the petrous to the superior hypophyseal segments of the ICA [65]. Since then, a second flow diverter stent (Surpass) has come to market. Flow diverter stents now have expanded indications, including smaller aneurysms, and aneurysm up to the internal carotid artery bifurcation. Recently, a multicenter group published a retrospective study of follow-ups after PED placement [66], in this report overall complications were 3.4% and in multivariate analysis older age > 70, larger diameter > 15 mm and fusiform were identified as independent variables with higher rates of incomplete occlusion in 6-month follow-up. However, currently there is not a standardized scale to report

**189**

**Figure 3.**

*Web Endoluminal bridge placement in left ICA bifurcation.*

*Endovascular Treatment of Brain Aneurysms DOI: http://dx.doi.org/10.5772/intechopen.88964*

will come to market.

radiographic outcomes that can be useful to meta-analysis studies or to new prospective randomized cohorts. Flow diverter stents are currently also limited usually to unruptured aneurysms, given the need for DAPT, however their use has found a niche in the treatment of ruptured blister aneurysms. Consequently, the next generation of this technology is looking into the possibility of special coating to mitigate the need for DAPT. Further investigation is still needed before this advancement

Although flow diversion devices can work out for many types of aneurysms as off-label uses; aneurysms located in bifurcations with wide neck and dome-to-neck ratio > 1 and < 2 remains a challenge for this technology. Therefore, the WEB device was created in regard of these concerns in flow diversion and has proven promising to overcome those limitations. The WEB device is placed intra-aneurysm with a subsequent change in the blood flow at the aneurysm neck [67]. In European multicenter prospective studies, the WEB device placed in basilar, MCA, Acomm and ICA bifurcation showed 2.7% of morbidity and at 1 year of follow-up, 56% of aneurysm complete occlusion [68]. Owing this method does not require to put the patient under DAPT unlike the PED, it can be used also in aSAH cases. Further investigation

All the patients that can be good candidates for PED placement based on their UIA characteristics needs also to be eligible for prolonged DAPT. Acetylsalicylic acid (ASA) plus clopidogrel is the DAPT of reference used for preventing thrombosis in such procedures [69]. The laboratory tests pre and post-procedure are yet to be standardized; due to the risk of clopidogrel resistant (28–68%) [70], is has been considered necessary to assess platelet reactivity. High platelet reactivity (HPR) is related with thromboembolic evens after stenting arteries [71]. Depending on institutional protocols, some neuro-interventional teams use the VerifyNow P2Y12 assay which has been widely studied however, the results of this tests may not be completely reliable [72] due to the fact that P2Y12 response units (PRU) cannot differentiate aspirin-induced platelet inhibition in patients administered clopidogrel. Other studies recommend the use of the Thromboelastography (TEG), which is dynamic and real time tool to measure clot formation. The advantages of VerifyNow assay is that can be done very fast with instant results, however in patients with programed procedures for UIA stenting this concerning may not be transcendental.

is needed as to the long-term outcomes for this device (**Figures 3** and **4**).

**3.8 Medical management after flow diverter placement**

**3.7 Flow disruptors and web endoluminal bridge (WEB)**

**Figure 2.** *Pipeline placement in a wide neck aneurysm in the left vertebral artery.*

*New Insight into Cerebrovascular Diseases - An Updated Comprehensive Review*

This method was developed in the 2000s. The concept of Flow Diversion is that a high-mesh density stent placed in the parent artery will disrupts blood flow into the aneurysm with the subsequent thrombosis of the aneurysm, this process takes 6 weeks to 6 months in average in radiographic follow-ups. Moreover, the stent in parent artery provides a scaffold for which endothelium can grow [62]. In 2011, the FDA approved the Pipeline Embolization Device (PED) for large or giant (≥10 mm) wide-necked intracranial aneurysms from the petrous to the superior hypophyseal segments of the ICA [65]. Since then, a second flow diverter stent (Surpass) has come to market. Flow diverter stents now have expanded indications, including smaller aneurysms, and aneurysm up to the internal carotid artery bifurcation. Recently, a multicenter group published a retrospective study of follow-ups after PED placement [66], in this report overall complications were 3.4% and in multivariate analysis older age > 70, larger diameter > 15 mm and fusiform were identified as independent variables with higher rates of incomplete occlusion in 6-month follow-up. However, currently there is not a standardized scale to report

**3.6 Flow diversion**

**188**

**Figure 2.**

*Pipeline placement in a wide neck aneurysm in the left vertebral artery.*

radiographic outcomes that can be useful to meta-analysis studies or to new prospective randomized cohorts. Flow diverter stents are currently also limited usually to unruptured aneurysms, given the need for DAPT, however their use has found a niche in the treatment of ruptured blister aneurysms. Consequently, the next generation of this technology is looking into the possibility of special coating to mitigate the need for DAPT. Further investigation is still needed before this advancement will come to market.
