Discussion

Preoperative embolization of cranial and spinal hemangioblastomas is used with the purpose of facilitating surgical resection of these lesions. Several different embolic agents have been used with the common goal of decreasing the arterial supply to the lesion with adequate capillary bed penetration.2–8 Embolic materials used include mechanical devices, and particulate and liquid embolic agents.2–9 Mechanical devices, such as coils, are able to occlude large feeders but they lack the ability to penetrate the tumor bed.5–7 Nonetheless, they may be used in combination with other agents providing more controllable embolization. Particulate agents such as polyvinyl alcohol and embospheres have also been employed. They provide temporary occlusion should the embolization be performed close to the scheduled surgical resection. Smaller particles have the advantage of better tumor bed penetration, achieving a greater degree of necrosis; however, their use also carries a higher risk of inadvertent non-target embolization.6 ,7 Liquid embolic agents (n-butyl cyanoacrylate (NBCA) and Onyx) have the best combination of durability and penetration, being able to devascularize the tumor reaching its core, and have been proposed by some authors.6 ,7 ,10 Embolization with NBCA requires significant expertise in the use of this agent and is not totally controllable, making precise delivery more difficult. In addition, it polymerizes quickly in contact with blood, increasing the risk of gluing the microcatheter in place.7 Onyx is a non-adhesive liquid embolic agent (ethylene-vinyl alcohol) dissolved in an organic solvent (dimethyl sulfoxide).11–13 Its major advantage compared with other embolic agents such as NBCA is non-adhesivity and increased predictability and control of deposition, which allows longer injections with controlled reflux and better penetration of the vascular channels.11–13

The safety and effectiveness of preoperative embolization of hemangioblastomas is still a matter of debate.2–9 Takeuchi et al reported their series of hemangioblastomas treated with preoperative embolization using primarily particles and concluded that presurgical embolization is useful to reduce operative complications when 80% or more of the tumor could be embolized (which was accomplished in only three of eight patients). Three patients had temporary neurological complications as a result of the embolization.5 In a series of five hemangioblastomas involving the cerebellum which were embolized with particles, Eskridge et al reported that surgical resection was easier and associated with less blood loss. One patient experienced worsening of hydrocephalus post-embolization, requiring emergency craniotomy and surgical resection.3 Biondi et al reported their series of preoperative embolization of the lower spinal region hemangioblastomas using particulate agents. Embolization caused no permanent morbidity and was thought to have decreased intraoperative bleeding.4 In another case report, a cerebellar hemangioblastoma was successfully embolized using particles and subsequently operated with minimal surgical bleeding.9 On the other hand, Cornelius et al compared the outcomes of particulate embolization of spinal and cerebellar hemangioblastomas. In his case series, all cerebellar hemangioblastomas (three patients) embolized were complicated by acute tumor bleeding and death. They hypothesize that tumor bleeding was a result of venous obstruction with congestion of the capillary bed with subsequent rupture.2 Montano et al reported a case of preoperative embolization of a cerebellar hemangioblastoma using particles complicated by permanent neurological deterioration due to tumor bleed.8

Few reports are available describing the use of Onyx in the treatment of hemangioblastomas.6 ,7 Gore et al reported two hemangioblastomas (one spinal and one cerebellar) that were successfully embolized with Onyx (the cerebellar hemangioblastoma was also embolized with NBCA).7 Horvathy et al described the presurgical embolization of a cerebellar hemangioblastoma using Onyx.6 The authors achieved complete angiographic devascularization without complications and, during surgical resection, the tumor was found to be avascular and was easily resected.

In our series of three patients, two patients with cerebellar hemangioblastomas were preoperatively embolized using Onyx. In both cases, >80% devascularization was achieved and there were no complications. Both lesions were resected on the following day after the embolization with minimal blood loss. Our third patient was embolized in a palliative manner using Onyx since his multiple comorbidities associated with the lesion location (medulla) made surgical resection not a viable option. In this case, preoperative MR revealed evidence of prior tumor hemorrhage. This patient was embolized via the supratonsillar branch of the left posterior inferior cerebellar artery resulting in >80% decrease in the supply to the tumor. The procedure was complicated by a small left lateral medullary infarct for with the patient subsequently recovered. MRI post-procedure demonstrated significantly decreased enhancement and size of the tumor. A follow-up MRI 6 months after the procedure demonstrated stable findings, supporting the notion that the lesion was indeed a hemangioblastoma as opposed to a malignant tumor.

Our experience suggests that preoperative embolization of hemangioblastomas with Onyx is feasible and effective in facilitating surgical resection. This is in accordance with other published reports.6 ,7 The safety of the procedure is still a matter of debate. As with any endovascular procedure, the risks of vessel damage, dissection, embolism, hemorrhage and stroke should always be taken into account. Our third case (patient No 3) had ischemic complications resulting in a left lateral medullary infarct. This type of complication is likely related to the lesion location (medulla) and was not seen when distal hemispheric branches of the cerebellar arteries were embolized (patient Nos 1 and 2). Tumor hemorrhage has not been reported and was not seen in our patients following Onyx embolization. As mentioned above, it has been hypothesized that tumor bleeding following particulate embolization is a result of venous obstruction with congestion of the capillary bed with subsequent rupture.2 This may explain why these devastating events have not yet been seen with Onyx embolization since both the arterial and capillary beds of the tumor are occluded by the Onyx in a progressive fashion before the agent reaches the venous outflow. We believe that, because of its embolic properties, Onyx may play an important role in the preoperative embolization of hemangioblastomas and other hypervascular cranial tumors. Nonetheless, large studies are still necessary to definitively assess the effectiveness and safety of these procedures and of this embolic agent (Onyx) in particular.