Indications

We are increasingly referred patients with a variety of tumors for consideration of preoperative embolization. In such cases, an a priori suspicion exists that the tumor is hypervascular, based on the tumor type, radiographic imaging, or possibly after a biopsy or attempted surgical resection at which time profuse bleeding was encountered. From an anatomic or technical standpoint, if embolization is deemed unfeasible or poses very high risk to a patient, it obviously should not be attempted. However, more commonly, the relevant question is not whether embolization is feasible but rather whether it is necessary. It is important to recognize that tumor hypervascularity alone is not a good reason to subject the patient to the added risk of preoperative embolization, particularly if the tumor is small, the major blood supply to the tumor is superficial or readily accessible early at surgery (as in most meningiomas), and/or if the extra blood loss anticipated without embolization is not excessive and would be physiologically well-tolerated by the patient. However, if substantial blood loss is anticipated without embolization beyond what would be medically acceptable in a given patient harboring a sizable tumor in a difficult surgical location with numerous deep, surgically inaccessible arterial feeders, the appeal of embolization becomes readily apparent. Embolization to devascularize a tumor may also decrease procedural time, which certainly increases convenience to the surgeon, decreases anesthesia time for the patient, and may or may not reduce the total cost of treatment. Overall, the combined risks of embolization and surgery should be less than that of surgery alone to benefit the patient. In any given case, several factors may impact the decision to offer preoperative tumor embolization ( Box 1 ).

Embolic Agents

Embolization Goals

Preoperative endovascular tumor embolization can be used to decrease overall blood loss; to improve visualization at surgery thus facilitating tumor resection; and/or to selectively occlude deep, inaccessible arterial feeders to the tumor. Transarterial embolization has been the traditional method to achieve these goals. Targeted embolization and occlusion of deep, prominent arterial feeders not accessible until late during the course of surgery is particularly useful for selected hypervascular tumors, where delicate microdissection and selective preservation of the normal, nontumor vasculature are necessitated by the site and local anatomy of the lesion. When multiple arterial feeders exist, transarterial occlusion of some may or may not result in significant overall tumor devascularization if others are left patent; however, if the remaining patent vessels are readily accessible at surgery, there may still be a significant benefit to selective embolization of only the deep feeders.

Even when near-complete or complete angiographic devascularization is achieved after preoperative feeding artery occlusion, surgeons may still note that the tumor bleeds significantly at surgery, reflecting collateralization and/or angiographically occult vascularization after embolization. It has been suggested but not substantiated that intraparenchymal tumor penetration of the embolic agent results in less operative blood loss compared with arterial feeding artery occlusion alone. Furthermore, it has been reported that intraparenchymal tumor penetration with Onyx is difficult to achieve by a transarterial route unless the microcatheter is situated within 2 cm of the tumor. In our experience, intraparenchymal tumor penetration of Onyx is best achieved by direct tumor puncture, which is an option in certain types of tumors ( Box 3 ), but obviously not all tumors can be accessed directly. Another advantage of embolization by direct puncture is that it offers the opportunity to achieve significant tumor devascularization while avoiding the need to catheterize multiple arterial feeders to the lesion, which may be difficult or dangerous to access transarterially.

Anesthesia

We prefer to perform all tumor embolization procedures with the patient fully anesthetized and intubated. This minimizes patient motion and allows for intermittent suspension of the patient’s respirations, which greatly enhances angiographic visualization during embolization. Furthermore, the DMSO in Onyx is angiotoxic and makes injection of this embolic agent quite painful and poorly tolerated in awake patients. For cooperative patients, intravenous sedation and appropriate analgesia without general anesthesia may be considered in selected cases, such as proximal segmental spinal artery occlusions using NBCA.

Angiography

Percutaneous transfemoral artery angiography is performed to delineate the extent of tumor blush, arterial supply, tumor flow dynamics, and venous drainage, and to identify important normal vasculature to be preserved. Using standard endovascular techniques, 5F guide catheters and DMSO-compatible microcatheters are generally used to access the target vessels leading to the tumor. Intravenous heparinization is initiated to achieve and maintain an activated clotting time of 200 to 300 seconds. A microangiogram should always be performed before embolization to ascertain tumor vascularity and identify any dangerous anastomoses to the adjacent normal vasculature.

Embolization

Liquid embolic embolization should be performed as close to the lesion as possible to achieve maximal intratumoral penetration of embolic material. Direct tumor puncture can be performed in selected cases using an 18-gauge spinal needle, with subsequent angiography and embolization carried out through the needle, as detailed previously. We typically use NBCA for distal feeding artery occlusion in cases where Onyx embolization is believed to be either too risky or unnecessary. For example, if the local vascular anatomy is such that deep intratumoral penetration of Onyx poses a high risk of nontarget embolization into important adjacent vessels, or if there is not enough of a safe distance proximally on the target vessel to allow for enough Onyx reflux to form an adequate “plug” (which must occur before the Onyx is able to be “pushed” forward), then we favor NBCA to achieve a focal occlusion of the target vessel. In selected tumors with rapid arteriovenous shunting, in which there is concern that an injected liquid embolic agent may inadvertently flow through the lesion and into the venous side, coils may be deployed first to partially devascularize the tumor, making it safer to then use the desired liquid embolic agent.

In those instances where distal selective catheterization is not possible, we prefer to use PVA particles for preoperative tumor embolization. This requires a slightly larger microcatheter than those used for liquid embolic embolization and also demands a careful review of the local vascular anatomy to identify potentially dangerous collaterals and to choose appropriately sized particles.

Postprocedure Care

After embolization, follow-up angiography demonstrates the extent of tumor devascularization and is also necessary to evaluate patency of the important adjacent normal vasculature. Intravenous steroids are often given to mitigate the expected peritumoral edema that occurs as a consequence of embolization. Routine postangiography care includes groin and distal pulse checks and frequent neurologic examinations to detect any clinical deterioration, which may be secondary to ischemia, hemorrhage, or postembolization tumor swelling.