• Most commonly encountered benign intracranial mass
  
• Derive from arachnoid cap cells and can be highly vascular
  
• Embolization to improve surgical outcomes and reduce intraoperative blood loss
  
• Widespread use to all meningiomas is not advised given the additional risk of the procedure and the limited benefit in small superficial lesions.

• All patients undergo preoperative testing, including electrolytes, blood urea nitrogen/creatinine and glomerular filtration rate; patients with borderline renal function should undergo intravenous (IV) bicarbonate administration with oral N-acetylcysteine.
  
• Careful examination of magnetic resonance imaging/computed tomography with contrast to determine possible target vessels of study
  
• Maintain IV hydration using isotonic fluids (normal saline or lactated Ringer’s solution) during and postprocedure.
  
• Administer steroids and antiepileptic agent prior to embolization in anticipation of the possible increased cytotoxic edema following embolization.
  
• A lucid understanding of the vascular anatomy is required to successfully and safely perform embolization of meningiomas.

Vascular Anatomy

• Convexity and falx meningiomas are usually supplied by the middle meningeal artery (MMA), anterior falcine branch of the anterior ethmoidal, or anterior or posterior cerebral artery branches.
  
• The MMA often supplies sphenoid wing meningiomas; petroclival tumors may also be supplied by the meningohypophyseal branch of the ICA or from the neuromeningeal trunk of the ascending pharyngeal artery. Olfactory groove tumors typically are supplied from the anterior or posterior ethmoidal arteries.
  
• Posterior fossa meningiomas often receive supply from the occipital artery via transosseous perforators and from the posterior meningeal artery. Tentorial meningiomas can be supplied by the meningohypophyseal trunk via the artery of Bernasconi and Casinari.
  
• Cerebellopontine angle tumors can be supplied by the MMA or the ascending pharyngeal, occipital, or subarcuate arteries. Foramen magnum meningiomas can be supplied from occipital or ascending pharyngeal artery branches.
  
• Parasellar meningiomas may have multiple feeders from the ICA as well as the MMA, accessory meningeal, or internal maxillary arteries.

Special Equipment

• 4 French (F) diagnostic catheter (UCSF-2 or Berenstein-2; Cordis, Bridgewater, NJ) and 0.035 in hydrophilic guide wire (Terumo glidewire, Terumo, Somerset, NJ)
  
• 5F guide catheter (Envoy MPD or MPC, Cordis) for intervention
  
• Microcatheter system (SL-10 or Excel 14, Boston Scientific); if using Onyx (ethylene-vinyl alcohol copolymer [EVOH]/dimethyl sulfoxide [DMSO]) ensure DMSO-compatibility of microcatheter
  
• Shapeable and ultranavigable 0.014 microwire (Synchro-2, Boston Scientific) for intracranial navigation

• For tumor embolization, the ideal embolic material would propagate to the tumor capillaries to maximize tissue devascularization and necrosis. Smaller particles can travel through vasa nervorum or occlude adjacent normal tissue; larger particles are more likely to lodge proximally and fail to reach tumor capillaries.
  
• Three major classes of embolic materials for meningioma devascularization:
  
  
  
  
  • Particulate Embolic Agent
    
    
    
    
    • Polyvinyl alcohol particles (irregular-shaped) or trisacryl gel microspheres (Embosphere; more uniform spheres) come in size ranges spanning 50 to 500 mcm. Do not use size < 150 mcm if significant risk of any reflux. Smaller 10-size microcatheters will enable easier distal navigation but cannot accommodate larger particles and are more prone to sludging, necessitating use of a more dilute particle solution.
    
    
  • Liquid Embolic Agent
    
    
    
    
    • N-butyl cyanoacrylate (NBCA) results in rapid polymerization when in contact with sodium, which can be slowed by admixing glacial acetic acid. NBCA is more difficult to control compared with EVOH, which polymerizes by diffusion of DMSO solvent. Onyx is available in two densities and enables better penetration. Caution: Onyx also can combust when it contacts monopolar cautery.
    
    
  • Occlusive Coils
    
    
    
    
    • Coils are used mainly following particulate embolization to further promote thrombosis and decrease risk of recanalization by flow reduction/interruption. Ideally, thrombogenic fibered coils should be used, otherwise hydrogel-coated (HydroCoil, MicroVention, Tustin, CA) or soft coils packed to a high density are also suitable.

Anesthesia Issues

• Most cases can be performed under monitored anesthesia, unless patient is noncooperative.
  
• Consider general anesthesia if meningioma is near critical vascular anastomoses where optimal angiographic visualization is essential. Obtain temporary apnea during angiographic run or critical roadmap.
  
• Microinjection using 1 mL of 1% lidocaine prior to use of NBCA or EVOH/DMSO to avoid excruciating dural pain.

Monitoring

• Provocative test microinjection using 1 mL of 1% lidocaine when near critical cranial nerve vascular supply
  
• Always test injection with contrast prior to injection of embolic agent to evaluate rate of flow and assess for changes mid-embolization.
  
• If patient is awake, perform appropriate focused neurologic testing before and after embolization of each pedicle to rule out new embolization-induced deficit.

For Particulate Embolization

• Maintenance of flow around microcatheter is critical to carry particles to distal tumor bed (do not wedge microcatheter); always check for mechanical vasospasm.
  
  
  
  
  • Do not use particles smaller than 100 mcm in critical territories or near anastomoses.
    
  • Use a dilute particle solution and use pulsatile injection to avoid sludging in microcatheter, which can lead to occlusion.
    
  • In case of increased flow resistance, avoid high-pressure injection, which could lead to proximal rupture of particle-laden microcatheter (withdraw and discard latter).
    
  • Always consider the remaining particles within the microcatheter dead-space when nearing stasis point.
    
  • After embolization to complete stasis, consider proximal coiling of pedicle to decrease likelihood of recanalization until craniotomy is performed.

For Liquid Embolization

Closure

• At the end of the procedure, remove guide catheter, perform postembolization diagnostic angiogram, and evaluate need for additional treatment; rule out normal vessel branch occlusion.
  
• Obtain postembolization ACT and consider partial heparin reversal with slow protamine infusion if ACT is greater than one and a half times baseline in absence of ischemic deficit.
  
• Image sheath insertion site and consider using a collagen-based closure device (Angio-Seal), umbrella-type assistive device (Boomerang, Cardiva Medical, Inc., Sunnyvale, CA) or simple manual compression.