Endovascular Management of Intracranial Aneurysms

Technique

At our institution, all intracranial aneurysm coiling procedures are performed under general anesthesia with neurologic monitoring, though other centers have described experience with local anesthesia and conscious sedation. An arterial line is placed in the radial artery to closely monitor the patient’s blood pressure, and for ruptured aneurysms, an external ventricular drain is placed prior to the procedure. The anesthesiologist is aware of the need to avoid transient blood pressure spikes, especially when intubating or extubating the patient. This is particularly important in patients who have a ruptured aneurysm. The case can sometimes take a few hours; therefore, anesthesia is necessary to maintain immobility because three-dimensional (3D) imaging and a fluoroscopic road map are very motion sensitive. A 6-French (Fr) sheath is inserted into the right common femoral artery, or alternatively in the radial artery. If balloon remodeling or additional microcatheters are needed, a larger sheath or puncture of the left common femoral artery may be necessary. Just after the sheath is inserted, a baseline activated clotting time (ACT) is drawn. For patients with unruptured aneurysms, 6 to 10 international units (IUs) of heparin per kilogram of body weight are given intravenously as a bolus. The ACT is checked every 30 minutes throughout the procedure, and heparin is given intermittently to keep the ACT between 250 and 300 seconds. For patients with ruptured aneurysms, 1000 to 3000 IUs of heparin are given after placement of framing coils; the patient is given additional heparin to maintain an ACT range of 250 to 300 seconds. A syringe of protamine is prepared in advance and readily available to be injected in case of aneurysm rupture. The usual dose is 10 mg of protamine per 1000 IUs of heparin. The goal is an ACT of less than 150 seconds. Likewise, for patients with unruptured aneurysms who have been treated preoperatively with dual antiplatelet therapy, a five-pack of unpooled platelets is maintained in case of rupture.

Patients who have not suffered a recent SAH are preoperatively given 75 mg of clopidogrel (Plavix) and 325 mg of aspirin orally starting 7 days prior to the procedure to prevent thromboembolic complications, with VerifyNow assays used to confirm aspirin and Plavix responsiveness, and alternative antiplatelet agents (ticagrelor, prasugrel, others) used for nonresponders, since approximately 25% of patients will have clopidogrel or aspirin resistance. ^, If emergent platelet inhibition is needed, the patient is loaded with a single dose of 600 mg of clopidogrel and 650 mg of aspirin. Full platelet inhibition occurs 2 hours afterward. If the procedure needs to be performed urgently, the patient may be given a glycoprotein IIb/IIIa inhibitor.

A complete cerebral angiogram is performed prior to treatment with a 4- or 5-Fr catheter, including bilateral common carotid artery, internal carotid artery, and vertebral artery injections. Complex reverse curve–shaped catheters (Simmons) or adjunct microcatheters allowing high flow injections may be used in cases of difficult or tortuous anatomy. Additional 3D rotational images are obtained to more accurately define the neck, dome, and size of the aneurysm. Once the diagnostic portion of the procedure is performed, the catheter is exchanged for a 6-Fr guide catheter, which is positioned as close as possible to the aneurysm to achieve the stability necessary to introduce a microcatheter safely into the aneurysm. Optimal stability of the guide catheter allows the operator to monitor the guide position on the same road map as the microcatheter during advancement of the coil into the aneurysm. Flexible guide catheters, including sometimes intermediate or distal access catheters, can be introduced farther into the intracranial circulation and can be routinely placed in the cavernous internal carotid artery or the basilar artery. This allows more stability for advancing devices into the intracranial circulation. If additional stability is needed to treat an aneurysm, a triple coaxial system consisting of a long sheath introduced into the origin of the great vessel followed by a guide catheter through this may offer enhanced stability in advancing devices through tortuous anatomy for the treatment of intracranial aneurysms. If an aneurysm cannot be treated from a femoral artery approach, a brachial, radial, direct carotid, or vertebral artery puncture is another option. Radial access is increasingly being used for angiography and embolization of intracranial aneurysms, relying largely on the cardiology literature suggesting safer outcomes with radial access.

Coil Selection

The choice of coil is made based on the size and shape of the aneurysm as seen on the angiogram and 3D reconstruction. The purpose of the first coil (framing coil or complex shaped coil) is to create a support basket for the subsequent introduction of additional coils and to provide a bridge to prevent additional coils from migrating into the parent vessel. The first coil is sized to the largest dimension of the aneurysm sac. The first coil should be as large and long as possible to fully appose the aneurysm wall and provide a nice basket and stability, thus preventing the coil from prolapsing into the parent vessel. This also provides the maximum number of coil loops across the neck of the aneurysm, thus preventing herniation of additional coils placed into the aneurysm from compromising the parent vessel.

If the aneurysm sac has a sausage appearance, then the principles guiding the selection of the first coil are different. In such aneurysms, a helical coil is preferred to a complex shaped coil and the first coil is sized to the smallest sac diameter. The subsequent coils are similar in size and length, with the aneurysm coiled from the dome toward the neck.

Coil Placement

Through the microcatheter, the platinum portion of the coil is introduced into the aneurysm sac while still on the delivery wire. In the microcatheter, the coil assumes a straight configuration; however, as soon as the coil leaves the microcatheter, it assumes the manufactured memory shape. The coil is radiopaque under fluoroscopy and is visualized under the live road map as it is placed into the aneurysm sac with the neck in profile. There should be limited resistance when introducing the coil into the aneurysm sac. If there is any resistance, the coil may be oversized. To prevent possible rupture, it is important to not force the coil into the aneurysm sac. If the coil is correctly sized, it will readily adapt to the shape of the aneurysm. If the coil is undersized, it will not be stable within the aneurysm sac and may herniate into the parent vessel. If the coil is oversized, it will not form with the aneurysm sac and will herniate into the parent vessel. Oversizing the coil may also cause excessive pressure on the wall of the aneurysm sac, possibly risking perforation.

Before detachment of the coil, an angiogram is performed to determine how the coil is confined within the aneurysm sac and whether there is compromise of the parent vessel. Movement of the coil during the angiogram may indicate that the coil is undersized and may migrate out of the aneurysm sac after detachment. If the coil appears properly sized and there is no compromise of the parent vessel, the coil is detached under fluoroscopy. The detachment wire is then slowly pulled back through the microcatheter to make sure the coil has detached from the wire and does not move.

Additional coils of various sizes and shapes are subsequently introduced into the aneurysm sac until the aneurysm sac is densely packed and is no longer filling with contrast or until the microcatheter is pushed outside the aneurysm sac. The first coils used for treatment of intracranial aneurysms were made out of platinum, but there were aneurysm recurrences after treatment; therefore, bioactive coils were introduced with the goal of inducing an exuberant healing response and improved filling volume of the coiled aneurysm. The first bioactive coil was the Matrix (Boston Scientific Neurovascular, Fremont, CA), introduced in 2002. The FDA approved the Matrix coil based on equivalency with the conventional GDC coil. More modern bioactive coils, which include finishing coils designed to be placed near the aneurysm neck, have been demonstrated to have high occlusion rates with low treatment-related morbidity. There is some evidence to suggest bioactive coils lead to higher rates of radiographic occlusion, though the clinical significance is unclear. Multiple bioactive coils are now available for clinical use: including the Matrix, HydroSoft family (MicroVention, Aliso Viejo, CA), Cerecyte (Micrus, Sunnyvale, CA), and Nexus. Results of a large multicenter trial using bioactive coils showed a 1.8% major complication rate, with a complete/near complete occlusion rate of 88%. The newer coils are manufactured so that the aneurysm sac is filled in a Russian nesting doll manner, from the periphery toward the center. Filling coils are placed into the aneurysm sac after the placement of framing coils; once the aneurysm is nearly densely packed, the final coils usually placed into the aneurysm sac are finishing coils. These coils are very short and soft. Once the aneurysm is densely packed, the microcatheter is removed slowly from the aneurysm, and a post-treatment angiogram is performed to assess the degree of aneurysm occlusion, parent vessel, and patency of the distal vasculature.

The heparin is reversed after the procedure with protamine and manual pressure, or a closure device is utilized to obtain hemostasis at the femoral puncture site. Newer closure devices with no permanent intraluminal component or using a stitch are designed to be less traumatic to the vessel. Pressure is usually held on the puncture site for 20 to 30 minutes after removal of the sheath if manual compression is utilized, and the leg is immobilized for 6 hours to prevent groin complications. If a closure device is utilized, ambulation can occur as early as 2 hours after placement. ^, In the case of radial access, pressure can be applied with the use of a compression band, with a balloon inflated at the wrist and depressurized sequentially. If there is compromise of the parent vessel, protrusion of coils, or thrombus formation during the coiling procedure, the heparin may be continued overnight with the sheath left in place. Antiplatelet therapy may also be given.

After endovascular treatment of nonruptured intracranial aneurysms, the patient is kept in the neurointensive care unit (NICU) for at least 24 hours for close monitoring of blood pressure, neurologic status, and puncture site. SAH patients are kept in the NICU for at least 14 days under close neuromonitoring and are prophalytically treated for vasospasm.

Results of Endovascular Treatment for Ruptured Aneurysms

Three prospective randomized trials have compared outcomes of endovascular coiling versus surgical clipping of ruptured aneurysms. The first study was performed in Finland and randomized 109 patients with SAH who were suitable for either surgery or endovascular coiling. Angiographic outcome in the posterior circulation was significantly better for endovascular coiling, whereas angiographic outcome in the anterior circulation was significantly better for surgery. Angiographic outcomes in the internal carotid artery and middle cerebral artery were similar in both groups. The Glasgow Outcome Scale was equivalent in both groups at 3 months. Mortality for technical reasons during surgery was twice that of the endovascular group (4% vs. 2%). One patient in the endovascular group suffered rebleeding following incomplete coiling of the aneurysm.

The second study was the ISAT, ^, which randomized over 2000 patients predominantly from Europe and with SAH and an aneurysm judged amenable to either surgery or endovascular treatment. Notably, only 2143 of 9559 (22%) of SAH patients screened met criteria for inclusion and entered the study. Outcome analysis on the basis of death or dependence at 2 months and 1 year based on the modified Rankin Scale (mRS) score was the primary parameter of interest in the first publication in 2002. At 1-year postprocedure, 250 of 1063 (23.5%) of the endovascular patients were dead or dependent, while 326 of 1055 (30.9%) of surgical patients were dead. This represents an absolute risk reduction of 7.4% for those treated from an endovascular approach. Delayed rebleeding was more common in the endovascular group; however, several cases were due to incomplete treatments. Seizures were also less common in the endovascular group.

The BRAT was a single-center trial with broader inclusion criteria, enrolling 500 consecutive SAH patients and randomizing to surgical or endovascular treatment without consideration of aneurysm anatomy or location. Cross-over was at the discretion of the treating physician, and occurred in 38% (75/199) of patients assigned to coiling, but only 2% (4/209) of patients assigned to clipping. While the study was underpowered to show small differences, interim reports at 1, 3, and 6 years showed that when analyzed from an intention-to-treat standpoint, mRS outcomes were similar in anterior circulation aneurysms at most timepoints, with an advantage for endovascular treatment in posterior circulation aneurysms.

The most recent guidelines for treatment of SAH offer Class 1 recommendations that, “for patients with ruptured aneurysms judged to be technically amenable to both endovascular coiling and neurosurgical clipping, endovascular coiling should be considered,” and “determination of aneurysm treatment, as judged by both experienced cerebrovascular surgeons and endovascular specialists, should be a multidisciplinary decision based on characteristics of the patient and the aneurysm.”

Results of Endovascular Treatment for Unruptured Aneurysms

The treatment of unruptured aneurysms is controversial, and no prospectively randomized trial has been performed comparing endovascular versus microsurgical management. A review of modern large clipping and coiling trials for unruptured aneurysms was published in 2005. A majority of these trials were nonrandomized and retrospective. Adverse outcomes were estimated at 8.8% for endovascular coiling and 17.8% for clipping. The International Study of Unruptured Intracranial Aneurysm adverse outcomes were less common with endovascular treatment (9.3%) than with surgery (13.7%); however, the study was nonrandomized, and the endovascular treatment group included a higher number of elderly patients, larger aneurysms, and aneurysms within the posterior circulation. Surgical adverse outcomes in this study correlated with patient age greater than 50 years, aneurysm size greater than 12 mm, location in the posterior circulation, previous ischemic cerebrovascular disease, and symptoms of mass effect from the aneurysm. Endovascular outcomes were less influenced by these factors. A review of population-level administrative database studies found, in general, higher rates of ischemic or hemorrhagic complications among patients treated surgically compared to endovascularly, though again these studies were nonrandomized and retrospective and lacked granular data on aneurysm type and size as well as patient outcomes. Additional unruptured aneurysm trials are needed.

Balloon Remodeling Technique