Preoperative Planning

A thorough preoperative medical history, detailed neurologic examination, and appropriate serologic analysis can reveal a contrast allergy or renal insufficiency before catheter angiography. Premedication, hydration, and/or minimization of contrast agent may be warranted in these patient populations. Patients often present to the neurosurgeon with a basic MRI study. However, in some cases (sella region, cerebellopontine angle), a fine cut MRI, with and without contrast, is useful for precise anatomic tumor localization. A computed tomography scan may be beneficial in identifying lesional calcifications. These studies will guide both the operative planning and the determinations of whether or not to evaluate the tumor angiographically. Surgeons can consider preoperative MRI or computed tomography angiography to help elucidate whether the tumor may benefit from embolization before submitting the patient to the risks of catheter angiography.

A preoperative diagnostic catheter angiogram should include, as appropriate, selective evaluation of the ECA, ICA, vertebral arteries, and, if location of the tumor warrants, the thyrocervical and costocervical trunks (typically cervicomedullary or spinal tumors). A bilateral evaluation is critical for parasagittal tumors, because they can recruit blood supply from both sides ( Fig. 1 ). Detailed angiographic information assists in guiding the embolization and aids the surgeon with preoperative planning (eg, identification of arterial feeders to be encountered and patency of dural sinuses). Often, the arterial pedicles directly supplying the meningioma must be selected to identify anastomoses that place cranial nerves and key structures at risk during embolization (discussed elsewhere in this paper).

Parasagittal convexity meningioma. ( A ) Coronal MRI with contrast. ( B ) Superselective angiogram in the anteroposterior (AP) projection of the right middle meningeal artery illustrating contralateral vascular supply that crosses the midline. ( C ) AP and ( D ) lateral superselective angiograms of the left superficial temporal artery demonstrating transosseous vascular supply to the tumor.

( From Mack WJ, Vinuela F. Diagnostic evaluation and embolization of meningiomas. In: De Monte F, McDermott MW, Al-Mefty O, editors. Al- Mefty’s meningiomas. 2nd edition. New York: Thieme; 2011. p. 123. Available at: www.thieme.com ; with permission.)

The blood supply to meningiomas arises from the ECA in addition to dural branches of the vertebral and ICA. However, meningiomas can also recruit substantial supply from cortical, pial, and/or scalp–transosseous arteries (see Fig. 1 ). Typically, meningiomas exhibit an intense vascular tumor blush that lasts through the late venous phase on angiography. Superselective angiography of feeding arteries often demonstrates a “sunburst” pattern of tumor staining.

Timing

Once it is decided to undertake preoperative meningioma embolization, the next consideration is timing. Although no consensus exists, most authors suggest that preoperative embolization should take place shortly before open resection, typically within a few days. Should embolization be performed on the same day as resection, it is prudent to examine the patient’s neurologic function between procedures. One study supports delaying surgical resection for at least 24 hours after embolization, exhibiting a reduction in blood loss after a 24-hour delay; however, optimal latency was not quantified. Kai and colleagues propose that the optimal duration between embolization and resection may be 7 to 9 days. The group demonstrates maximal tumor softening, decreased operative times, and lower Simpson grades at this delayed time point. A similar study compared 16 patients with tumor embolization 7 days or greater from the time of resection with a group of 12 patients who underwent surgery less than 7 days from embolization. The authors showed greater reduction in surgical time and blood transfusion volume in the delayed embolization group. However, delayed resection also may allow for tumoral edema and resultant mass effect. Smaller particles (60–150 μm) have better tumor penetration, but can also increase the risk of swelling. This should be considered, especially in the setting of delayed tumor resection. A course of steroids during and after procedures involving high tumor volumes may be warranted; however, the surgeon should still be prepared for emergent decompression and resection if tumoral edema results in neurologic decline, new cranial nerve deficits attributable to compression, or significant mass effect on follow-up imaging. Postembolization tumoral edema can be expected anywhere from a few hours to several days after and the patient should be watched closely, particularly in high-risk tumor locations ,such as the posterior or middle fossa.

Preparation and Patient Positioning

The biplane digital subtraction fluoroscopy suite should be prepared in a similar fashion as for any neuroendovascular procedure. Anesthesia options include intravenous sedation, monitored anesthesia care, and general endotracheal anesthesia. When the sedation or monitored anesthesia care option is selected, precise angiographic evaluation of very small dangerous anastomotic channels immediately before embolization requires an extremely cooperative patient who can remain still during image acquisition. If the patient is under general anesthesia, electrophysiologic monitoring can increase procedural safety.

Endovascular Technique

Once ready for embolization, a microcatheter and microguidewire are navigated coaxially through the guide catheter, and distally into the arterial pedicle through which embolization is planned. A microcatheter injection can be performed to identify the microanatomic angioarchitecture of the arterial supply to the meningioma. Microangiography can also aide in the identification of any dangerous anastomoses or blood supply to at-risk cranial nerves. The microcatheter is then navigated more distally, beyond any concerning anatomy, to a position as close as possible to the tumor vascular bed ( Fig. 2 ). Reflux of contrast proximally along the catheter is evaluated. Such contrast reflux can predict the potential for reflux of embolic agents. Thus, identification can help to prevent unwanted embolization of more proximally located high-risk branches or the parent artery. Provocative testing with injection of amytal and/or lidocaine can help to identify possible complications of embolization. Either neuromonitoring or immediate neurologic examination helps to identify the effect of the provocative testing.

Right sphenoid wing meningioma. ( A ) Right external carotid artery and ( B ) selective right middle meningeal artery angiograms demonstrate the characteristic vascular blush of a right sphenoid wing meningioma, deriving arterial supply predominantly from branches of the right middle meningeal artery. Note no choroidal blush from these injections. ( C ) Selective right middle meningeal artery angiogram after transarterial embolization of the tumor using polyvinyl alcohol 150 to 250 and 250 to 355 micron particles, resulting in significant devascularization of the meningioma. ( D ) Right common carotid artery angiogram after subsequent coil embolization of the distal right middle meningeal artery trunk demonstrates near-complete devascularization of the tumor and truncation of the right middle meningeal artery. Note a small amount of residual vascular tumor blush arising from branches of the right inferolateral trunk off the cavernous segment of the right internal carotid artery.

Next, embolic material is chosen and, with the catheter in good position, it is injected into the tumor. This injection should be done slowly and under biplane fluoroscopy with close monitoring on both planes for reflux or aberrant flow of embolic material. If this occurs, injection should cease immediately. Embolization should continue until the embolic material fails to reach the tumor or unwanted reflux is noted. If particles are used, then embolization continues until slow or stagnant flow is seen in the feeding vessel. Often, embolization can lead to complete, or near complete, angiographic tumor devascularization without selection of all feeding vessels (see Fig. 2 ). If inadequate embolization occurs, further selection of vessels may be necessary. Upon completion of embolization, proximal contrast injection is warranted to assess the entire vascular tree.

Particles

A suspension of particles mixed with contrast agent is most common, offering good penetration and ease of use. Several types of particles of varying sizes are available for embolization. The type of particle varies in its visualization, compressibility, subsequent recovery, and ability to aggregate. Each of these factors impacts the choice of agent. Polyvinyl alcohol (PVA) particles are a common choice and available in preparations in a variety of predetermined size ranges. Recognized limitations include difficulty with aggregation, which can lead to microcatheter obstruction. If stoppage occurs, forced injection to clear the catheter is not recommended, because undesired embolization can result. Although smaller PVA particles have shown a greater ability to cause tumor necrosis owing to deeper penetration, smaller size also increases the risk for aberrant embolization to cranial nerves and other critical structures. In a larger observational study, the sole independent risk factor for complications, including cranial nerve deficits and tumor hemorrhage, was small particle size (45–150 μm). Particle size smaller than 150 μm is thought to increase the risk of embolization to the vasa nervorum of the cranial nerves. In most situations, particles with a diameter between 150 and 350 μm will provide optimal tumor penetration and decreased risk for undesired embolization. Tumors with higher flow input may require even larger particles (>500 μm), or an alternative strategy such as gelfoam, liquid embolic agents, or coils ( Fig. 3 ).

Suprasellar meningioma. ( A ) Coronal and ( B ) axial MRI demonstrating a homogenously enhancing mass that encases the bilateral internal carotid arteries. Lateral right internal carotid artery angiograms in the ( C ) arterial and ( D ) capillary phases demonstrating a suprasellar tumor blush supplied b enlarged dural branches of the meningohypophyseal trunk. ( E ) Superselective angiogram of the meningohypophyseal trunk. ( F ) A significant decrease in size and intensity of the tumor blush after polyvinyl alcohol and coil embolization of the meningohypophyseal branch supplying the tumor.

( From Mack WJ, Vinuela F. Diagnostic evaluation and embolization of meningiomas. In: De Monte F, McDermott MW, Al-Mefty O, editors. Al- Mefty’s meningiomas. 2nd edition. New York: Thieme; 2011. p. 128. Available at: www.thieme.com ; with permission.)

Made of tris-acryl and cellulose porous beads, microspheres have advantages and disadvantages when compared with PVA particles. The shape and size are more consistent, leaving less variability in advertised size. Additionally, they are more compressible than PVA particles, which helps to prevent the blockage of catheters. However, compressibility can also increase the risk of advancement into small vessels serving cranial nerves. One study comparing the 2 types of particles indicated that microspheres exhibited less intraoperative blood loss.

Liquid Embolic Agents

N -Butyl cyanoacrylate (NBCA; TRUFILL, Codman & Shurtleff, Inc, Raynham, MA) and ethylene vinyl alcohol (Onyx; Covidien-ev3 Neurovascular, Irvine, CA) are suspended polymers that solidify when they come into contact with blood. Liquid embolic agents can penetrate into small tumor vessels and are less likely than particles to result in recanalization over time. However, these agents can polymerize within the catheter, can penetrate into small anastomotic vessels, and cost more than particles. The operator must also be cognizant of potential catheter retention with long injections or tortuous anatomy. NBCA is mixed with ethiodol to various dilutions, which allows alteration of the rate of polymerization. Angiographic visibility is increased by adjustment of concentrations or addition of tantalum. Proper embolization with NBCA requires familiarity with the preparation. Advanced technical strategies, such as using coils to obstruct origins to dangerous anastomoses, can help to prevent inadvertent embolization of undesired areas. Advantages of Onyx include an ability to penetrate into tumor capillaries, predictability of solidification, deliberate and controlled injections, and radioopacity. In a small series, of meningiomas, no postembolization tumor edema or hemorrhagic complications were noted.

Other Embolic Agents

Additional agents have been used in meningioma embolization, but reports are limited. These include fibrin glue, ethyl alcohol, hydroxyapatite ceramics, phenytoin, hyperosmolar mannitol, and lipiodol. Although virtually all agents show good tumor penetration, each has advantages and disadvantages.