26 Flow Diversion Treatment of Intracranial Aneurysms
General Description
The flow diverter (FD) is a relatively new development in endovascular neurosurgery. There are several FDs currently available, each with its own nuances. Device selection is largely based on operator preference and experience. Devices include the pipeline embolization device (PED, Medtronic), Surpass (Stryker), the flow-redirection endoluminal device (FRED, MicroVention), Silk (Balt Extrusion), and the p64 (Phenox). Each device has its own specific characteristics with different lengths, filament size and number, design, and deployment. The most commonly used FD is the PED. The PED was initially utilized in North America by Fiorella et al. in 2008. 1 The FDA-approved indication for use included large, wide-necked aneurysms from the petrous portion of the internal carotid artery (ICA) to the paraclinoid ICA region. Many studies boast an 80%–90% overall aneurysm obliteration rate. In the Buenos Aires experience, Kallmes et al. 2 reported obliteration in 90% of intracranial aneurysms (IAs) at the 1-year follow-up and in 100% of IAs at 8 years. Flow diversion is now being utilized in some studies for small IAs as an alternative treatment to stent coiling or clipping.
The PED is a braided stent composed of 48 cobalt/chrome and platinum/tungsten wires providing 25%–35% metal coverage, depending on the size of the device. The device is available in diameters of 2.5–5 mm and lengths of 10–35 mm. When opened, the device is 0.25 mm larger than the stated diameter. Flow diversion works by mechanical redirection of blood flow, which allows for intra-aneurysmal stagnation of blood, eventually leading to vessel reconstruction via endothelialization along the device. Of note, perforators are typically spared during FD treatment if they are end vessels; however, care should be taken when deciding which aneurysms to treat because essential arterial perforators can be occluded. For long-segment vessel pathology, PEDs can be placed in tandem.
Indications
The PED is FDA-approved “for the endovascular treatment of adults (age 22 years and above) with large or giant wide-necked IAs in the ICA from the petrous to the superior hypophyseal segments.” Off-label uses include aneurysms of the middle cerebral artery, anterior cerebral artery, anterior communicating artery, and those of the posterior circulation. The PED has been used in ruptured aneurysms and blister aneurysms with good results.
Neuroendovascular Anatomy
Although some FDs are more flexible and trackable than others, these devices contain a large amount of metal. Thus, they must be advanced (“pushed”) via a pusher wire through a microcatheter to the location of interest. The degree of tortuosity from the groin (femoral artery) to the neck (carotid artery) must be assessed, and the proper guide catheters selected. Furthermore, tortuosity of the neck vessels and the carotid siphon can make it very difficult to push some devices. Perforators must also be assessed. Midbasilar device placement can have disastrous consequences because of the many pontine perforators; however, typically, the benefit of treating a midbasilar IA will outweigh the risk. Vessels such as the ophthalmic and anterior choroidal arteries should be preserved and a device landing zone selected with this in mind. Vessels leaving the apex of the aneurysm can decrease the effectiveness of the FD treatment. Rangel-Castilla et al. 3 reported a 15.8% occlusion rate for side-branch vessels covered with PED for aneurysm treatment. At the long-term follow-up, no occlusions were symptomatic.
Perioperative Medications
Given the large amount of metal coverage, a course of dual antiplatelet therapy is prescribed before the FD procedure and systemic heparinization is administered during FD deployment. Aspirin (325 mg daily) and clopidogrel (75 mg daily) are given for at least 5 days prior to device placement. Then, before the procedure, therapeutic platelet function testing (VerifyNow, Accriva Diagnostics) is conducted to monitor the presence and effectiveness of the antiplatelet medications. If the patient is a clopidogrel hypo- or nonresponder, ticagrelor (90 mg twice daily) can be used instead. If the patient was not started on dual antiplatelet therapy before the procedure, we administer abciximab (a glycoprotein IIb/IIIa platelet aggregation inhibitor) immediately after the placement of the first PED. Then, we administer 450 mg of clopidogrel and 325 mg of aspirin after the procedure. Clopidogrel (75 mg daily) or ticagrelor (90 mg twice daily) is maintained for at least 6 months. The patient remains on aspirin for life.
Specific Technique and Key Steps
After a femoral angiogram has been performed to confirm the absence of any irregularity or dissection, a guide catheter is placed over a curved wire/diagnostic catheter (e.g., 0.035-inch angled Glidewire, Terumo), and the system is advanced into the aorta under fluoroscopic guidance ( Fig. 26.1–26.10, Video 26.1–26.10 ).
The guide catheter should be placed in the extracranial vessel (ICA, common carotid artery, or vertebral artery) of choice utilizing roadmap navigation.
The intermediate catheter (Sofia catheter, MicroVention) or distal access catheter (DAC, Cook) is connected to the heparinized flush and introduced through the guide catheter. The use of an intermediate catheter is recommended in cases of moderate-to-severe vessel tortuosity ( Fig. 26.5, 26.6, Video 26.5, 26.6 ).
A 0.027-inch microcatheter (e.g., Marksman, Medtronic; Headway 27, MicroVention; or Excelsior XT-27, Stryker Neurovascular) is connected to a heparinized flush and introduced through the intermediate or guide catheter.
The correct working views of the aneurysm are identified on magnified anteroposterior and lateral fluoroscopy.
Under roadmap guidance, the intermediate catheter is navigated and placed 1–2 cm proximal to the aneurysm neck.
The microwire and microcatheter are advanced past the aneurysm neck. A distal purchase of 2 cm is recommended and is often necessary because of the stiff delivery system of the PED and its propensity to move the catheter out of position when navigating the device ( Video 26.1–26.10 ). (Note: for large aneurysms, the microwire and/or microcatheter may loop several times within the aneurysm before finding the distal ostium. Sometimes, a balloon in the distal vessel can assist with purchase for later straightening of the system ( Fig. 26.1, Video 26.1 ).)
Sizing is important because longer devices can twist during deployment, but if compacted, shorter devices will result in incomplete coverage of the aneurysm neck. The device that is selected is typically 1 mm wider than the proximal diameter of the parent vessel with at least 5 mm on either side of the aneurysm neck, depending on whether the device will need to incorporate a bend. If placing multiple devices in tandem, ensure a 30%–50% overlap to prevent endoleak or unwanted loss of access. Packing larger devices into small parent vessels does not automatically increase the metal coverage of the aneurysm neck. Incorrectly sized devices are likely to migrate and cause complications.
The landing zone must be carefully selected at least 1 cm distal to the aneurysm neck to ensure the FD does not prolapse into the aneurysm.
The FD is loaded into the 0.027-inch microcatheter. The plastic sheath that comes with the device should be back-flushed prior to pushing the device.
The FD is advanced until the tip of the delivery system is aligned with the microcatheter tip, and the catheter and PED are pulled back as a unit until the distal PED is in the desired zone ( Video 26.1–26.10 ).
The device is deployed by first retracting the microcatheter while keeping the PED in place. The PED is then further deployed by pushing on the delivery wire and retracting the microcatheter ( Video 26.1–26.10 ).
During deployment, the FD should not be stretched. Aim for the shape of a wine glass. If the device appears stretched, push the microcatheter and device (“load the system”) and try compacting the device via the pusher wire.
The FD is unsheathed via gentle retraction of the microcatheter with varying amounts of pushing on the pusher wire ( Video 26.1–26.10 ). Some operators will push the device through curves for better apposition and compress it near the neck. Bear in mind, the more the device is manipulated, the greater the chance that it will twist, which can be difficult to correct; however, swaying the device to and fro can sometimes fix unwanted twisting.
Once the FD has reached the point where it cannot be resheathed, you are committed to its deployment; prior to this, the device can be recaptured and redeployed.
After the device has been successfully deployed, a test run can be performed to ensure good approximation and some intra-aneurysmal flow stagnation ( Video 26.1–26.10 ). If the operator is satisfied, the microcatheter is brought through the stent to retrieve the pusher wire.
The pusher wire and microcatheter must be removed carefully to avoid stent migration. If the lesion requires tandem device placement, care should be taken to avoid losing device access by pushing the next device and repeating the above steps.
Final runs are obtained. Some contrast stagnation (indicating that flow is being diverted) within the aneurysm is usually noted. Ensure good device apposition, otherwise balloon angioplasty may be needed.
Device Selection
In our practice, the following are common set-ups and devices used for FD placement.
8F or 6F sheath.
8F guide catheter (90 cm Neuron MAX, Penumbra) or 6F guide catheter (Envoy XB DA, Codman Neuro).
Intermediate catheter (Navien, Medtronic), Sofia or Phenom (Medtronic).
0.027-inch microcatheter (Marksman, Headway 27, or Excelsior XT-27).
0.014-inch Synchro 2 standard wire (Stryker).
FD.
Continuous heparinized flush.
Pearls
In-stent thrombosis can occur and should be managed like any acute stroke with diagnostic angiography followed by either thrombectomy or glycoprotein IIb/IIIa inhibitor infusion.
A stretched or constrained device can be opened within the intermediate catheter and then deployed as a last resort.
Losing access to the device within a large aneurysm can be disastrous because the device can migrate or no longer align with the proximal vessel. Transcirculation maneuvers can be utilized to regain access by way of snaring of a microwire, buddy wires, or the FD and removal. Last resort options include balloon test occlusion and vessel sacrifice.
FDs have been used off-label for cases of failed stent-coil aneurysm treatment with good results ( Fig. 26.7–26.10, Video 26.7–26.10 ).
Large aneurysms in eloquent locations such as the midbasilar artery may benefit from heparinization in the postprocedure period to prevent massive thrombosis and perforator infarct ( Fig. 26.10, Video 26.10 ).
Large aneurysms can become more symptomatic following device placement. As the lesion swells during thrombosis, pain/symptoms can be treated with steroids. Although the risk is low, late rupture has been observed as a result of clot autolysis.
Deploying the device in a small diameter landing zone under tension can lead to foreshortening and prolapse of the device. Deploying the device within a large diameter landing zone can lead to less metal coverage distally, requiring two devices.
The first-generation PED could not be resheathed and more than one device was often necessary to cover the aneurysm neck. The second-generation PED, Pipeline Flex (Medtronic), can be resheathed and reimplanted in the proper position. This improvement in the delivery system has significantly decreased the need for multiple devices.
A PED can foreshorten and prolapse into the aneurysm. Maintaining the position of the microcatheter distal to the aneurysm is critical because finding the lumen of a deployed device can be quite difficult once access is lost.
References
[1] Fiorella D, Woo HH, Albuquerque FC, Nelson PK. Definitive reconstruction of circumferential, fusiform intracranial aneurysms with the pipeline embolization device. Neurosurgery. 2008;62(5):1115–1120. [2] Kallmes DF, Brinjikji W, Cekirge S, et al. Safety and efficacy of the pipeline embolization device for the treatment of intracranial aneurysms: A pooled analysis of 3 large studies. J Neurosurg. 2017;127(4):775–780. [3] Rangel-Castilla L, Munich SA, Jaleel N, et al. Patency of anterior circulation branch vessel after pipeline embolization: Longer-term results from 82 aneurysms cases. J Neurosurg. 2017;126(4):1064–1069.Case Overview: CASE 26.1 Cervical Internal Carotid Artery Aneurysm: Flow Diversion
A 49-year-old female presented with progressive pulsatile mass on the left anterior neck. She also described occasional tingling and numbness on the right upper and lower extremities. She denies any neck trauma; however, she remembers sudden left neck pain a few months prior to her current presentation. Her neurological examination was normal. She had a past medical history of hypertension, coronary artery diseases, and recent cardiac stent. The patient has been taking aspirin and clopidogrel.
Computed tomography (CT) and magnetic resonance angiogram (MRA) demonstrated a large cervical internal carotid artery (ICA) aneurysm.
Procedure
The patient underwent elective endovascular treatment of her cervical ICA with flow diversion stenting. Patient was given 325 mg aspirin and 75 mg clopidrogel daily for 7 days prior to the intervention. The procedure was performed under conscious sedation and through a right femoral artery approach. 5,000 units of heparin were given to obtain an activated clotting time of more than 250.
Device List
Femoral artery access.
Micropuncture kit (2).
6F dilator.
8F sheath.
0.035-inch Glidewire.
Neuron MAX 088 guide catheter (Penumbra).
0.027-inch Marksman microcatheter (Medtronic).
0.014-inch exchange length (300 cm) Synchro 2 microwire (Stryker).
4 x 15 mm HyperForm occlusion balloon (Medtronic).
5 x 20 mm Pipeline Embolization Device (PED) mm Flex (Medtronic).
8F AngioSeal percutaneous closure device.
Device Explanation
This large cervical ICA aneurysm or pseudoaneurysm is probably the result of an initial ICA dissection. Endovascular goals include angioplasty of the dissection/stenosis and stent reconstruction. There is no carotid stent that could accommodate to small caliber (3.5) of the ICA. Flow diversion stent (pipeline) is a good alternative for stent artery reconstruction and aneurysm treatment. A 4 x 15 mm balloon is advanced into the ICA and balloon angioplasty of the ICA stenosis/dissection segment is performed. Over the exchange length 0.014-inch microwire, the balloon is exchanged for the 0.027-inch microcatheter. A 5 x 20 mm PED is advanced and deployed across the aneurysm neck.
A device significantly larger in diameter than the parent artery was used to expand the vessel, reduce the stenosis, and create flow diversion on the aneurysm.
A pipeline stent conformed well to the artery tortuosity without altering the anatomy, whereas a carotid stent could have strengthened and kinked the vessel.
Tips, Tricks & Complication Avoidance
Flow diversion stenting with PED is an adequate alternative for the management of high cervical and skull base dissections (Oper Neurosurg (Hagerstown) 2018 [Epub ahead of print]).
We suggest using a PED larger than the diameter of the extracranial vessel to reduce the risk of significant stent foreshortening and the need of a second PED.
PED does not have enough radial force to treat extracranial vessel dissection or stenosis; therefore, we recommend balloon angioplasty prior to PED deployment.
Flow diversion stent (PED, Surpass) are adequate alternatives to carotid stents (Wallstent, Xact) in tortuous extracranial vessels. They are flexible and conform to vessel characteristics without the risk of vessel deformity resulting in straightening and kinking.
Case Overview: CASE 26.2 Internal Carotid Artery Cave Aneurysm: Flow Diversion
A 51-year-old female was found to have multiple intracranial aneurysms during work-up for migraines. She has a past medical history of chronic headaches, migraines and familial history of subarachnoid hemorrhage (SAH). Three previous aneurysms have been treated with endovascular coiling. Her neurological exam is normal.
Computed tomography (CT) angiogram demonstrated a medium-sized right internal carotid artery (ICA) wide-necked aneurysm.
Procedure
The patient underwent elective endovascular treatment of her ICA cave aneurysm with flow diversion stenting. Patient was given 325 mg aspirin and 75 mg clopidogrel daily for 7 days prior to the intervention. The procedure was performed under conscious sedation and through a right femoral artery approach. 5,000 units of heparin were given to obtain an activated clotting time of more than 250.
Device List
Femoral artery access.
Micropuncture kit (2).
6F sheath.
0.035-inch Glidewire.
Envoy XB DA guide catheter (Codman).
0.027-inch Marksman microcatheter (Medtronic).
0.014-inch Synchro 2 microwire (Stryker).
4 x 20 mm Pipeline Embolization Device (PED) flex (Medtronic).
6F AngioSeal percutaneous closure device.
Device Explanation
Currently, the majority of cavernous and paraclinoid ICA aneurysms are treated with flow diversion. This patient with multiple intracranial aneurysms treated endovascularly still has a cave ICA aneurysm that requires treatment. A 6F guide catheter is positioned at the petrous ICA. Under roadmap and navigation, a 0.027-inch microcatheter over a microwire is advanced into the middle cerebral artery. The microwire is exchanged for the PED. The PED is advanced until the tip of the delivery system is aligned with the microcatheter tip, and the catheter and PED are pulled back as a unit until the distal PED is in the desired location. We typically use the ICA bifurcation as the landing zone. The PED is deployed by retracting the microcatheter (unsheathing) while keeping the PED in place. By unsheathing the PED, it will create a “cigar” shape while it is still attached to the distal coil. Progressively continue unsheathing the PED until the end of the device fully expands and deploys.
The ICA and the carotid syphon had no tortuosity and a simple 6F guide catheter and microcatheter were sufficient for adequate and accurate placement of the PED.
Tips, Tricks & Complication Avoidance
Even though cavernous ICA aneurysms are usually managed conservatively because of the minuscule risk of SAH. Cave ICA aneurysms carry the risk of SAH because they are anatomically located within the subarachnoid space.
Pipeline Flex (Pipeline, 2nd generation) has a great advantage over the first-generation PED. It can be resheathed in up to 75% of unsheathed stent. Also, compared to the first PED, Pipeline Flex will always open after unsheathing without the need for additional maneuvers (e.g., device rotation). If the “cigar” shape is still maintained during stent deployment, the neurosurgeon should not be concerned, as the stent will ultimately open.
In patients with minimal-to-no cervical ICA or carotid syphon tortuosity, a simple 6F guide catheter with a soft distal end (Envoy XB DA [Codman] or Benchmark [Penumbra]) advanced at the petrous ICA offers sufficient support for microcatheter intracranial navigation. There is no need for intermediate catheter. Adding an intermediate catheter could increase the risk of thromboembolism complications.
Case Overview: CASE 26.3 Posterior Communicating Artery Aneurysm: Flow Diversion
A 46-year-old female was found to have multiple intracranial aneurysms during work-up for migraine. A previous aneurysm was treated with microsurgical clip ligation. Her neurological exam was normal. She has a history of familial subarachnoid hemorrhage.
A posterior communicating artery (PCoA) aneurysm has grown on follow-up imaging.
Procedure
The patient underwent elective endovascular treatment of her PCoA aneurysm with flow diversion stenting. Patient was given 325 mg aspirin and 75 mg clopidogrel daily for 7 days prior to the intervention. The procedure was performed under conscious sedation and through a right femoral artery approach. 5,000 units of heparin were given to obtain an activated clotting time of more than 250.
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