Embolization Technique

Diagnostic angiography and tumor embolization are performed 1 to 2 days before the scheduled surgical resection to allow time for tumor necrosis while avoiding neovascularization. However, some report waiting as long as 7 days between embolization and surgery.² The patient should be well hydrated before the commencement of angiography to protect renal function from the contrast material.

The diagnostic angiogram is extremely important to identify not only the vascular supply to the tumor but also dangerous anastomoses. In-depth knowledge of anatomy and potential external carotid–to–internal carotid anastomoses is essential for performing tumor embolization safely and effectively.⁴ The most common anastomoses that one must evaluate are listed in Table 110-1. The other pitfall that must be avoided is embolizing the vascular supply to the cranial nerves and roots. Knowledge of the anatomy is essential; however, one should exercise caution and know that vascular distributions are highly variable. If any doubts remain, administering 3 mL of lidocaine and testing for cranial nerve deficits can be performed before embolization.² Table 110-2 lists the common vascular supply to the cranial nerves and roots. In addition, amobarbital may be used to assess the arterial blood supply to the brain parenchyma.^5,6 Monitored anesthesia care is necessary to perform provocative testing. However, some patients cannot tolerate monitored anesthesia care and therefore require general anesthesia. Although general anesthesia negates the use of provocative testing, it does provide some benefits, such as increasing the accuracy of angiography (less motion artifact) and patient comfort (manipulation inside the middle meningeal artery can produce extreme discomfort). Continuous electroencephalographic monitoring along with somatosensory evoked potentials can provide insight that a complication has occurred when general anesthesia is used.

TABLE 110-2 Cranial Nerve Blood Supply from Potentially Embolized Vessels

ICA, internal carotid artery.

Once the diagnostic angiogram is performed and it is deemed safe to continue with the embolization, the patient is given 10 mg of dexamethasone and fully heparinized before insertion of the microcatheter and guide catheter. Dexamethasone is administered to help with the potential postoperative edema, and the patient should be heparinized to at least two times the baseline activated clotting time to prevent the formation of emboli from the catheters.

A microcatheter and microguidewire are selectively placed, under digital subtraction angiography and road map guidance, into a feeding vessel as close to the tumor as possible. The guidewire is removed and the embolic agent injected under continuous road map imaging to ensure that it does not reflux around the catheter, travel through anastomoses previously not visualized, be deposited in brain parenchyma, or travel beyond the tumor bed into the venous system. Once this feeding arterial supply is completely embolized, the catheter is then selectively placed into another feeding vessel (that is safe to embolize), and the process is repeated. The embolization procedure is complete when no tumor blush is visualized or no other feeding vessel can be safely embolized. It is important to emphasize that embolization should take place at the tumor bed itself and not just at the proximal feeding artery. Occlusion of the proximal feeding artery alone will result only in the formation of collateral blood supply and ineffective embolization. After embolization, the patient is maintained on steroid therapy and admitted for observation.

Embolic Agents

Several different agents can be used for tumor embolization (Table 110-3). The agents fall into one of three main categories: liquids, particulates, or coils. The agent selected depends on the presence or possibility of a dangerous anastomosis, the ability to navigate the microcatheter to the ideal location, vascular supply to the cranial nerves, and operator preference. The vasa nervorum are usually less than 150 to 200 µm; therefore, if cranial nerves are at risk, it is recommended that embolic agents larger than 200 µm in size be used.⁴ The best embolization results are achieved with small or liquid agents that can penetrate the tumor bed and embolize at the capillary level. These agents are also the most dangerous to use because they can damage normal structures as well. Large embolic agents, such as coils or particles larger than 500 µm, are relatively safe but are ineffective if used alone. A good mixture of safety and efficacy is achieved when embolic agents ranging in size from 300 to 500 µm are used.⁴

TABLE 110-3 Classification of Embolic Agents

ETOH, ethyl alcohol; NBCA, N-butylcyanoacrylate; PVA, polyvinyl alcohol.

Efficacy