Meningiomas are typically treated through surgical resection if large and with symptoms related to mass effect. However, these tumors are often hypervascular and surgical resection can lead to significant blood loss if en bloc resection is not possible.2) Preoperative embolization has been demonstrated to decrease operative times, surgical blood loss, infection rates, and concomitant risks of anesthesia. Additionally, the surgical resection is often made less arduous technically due to softening of the tumor.9)10)

Various agents have been described in preoperative tumor embolization, with the most common being polyvinyl alcohol (PVA).10) Other described agents include gelatin microspheres, alcohol, gelfoam powder and liquid agents including n-butylcyanoacrylate (NBCA) and Onyx.10) Taki et al. first introduced the use of Onyx as a new liquid non adhesive material in the embolization of three cerebral arteriovenous malformations (AVMs).12) Onyx has now become a well-accepted method for embolizing AVMs.7) Its use in embolization of meningiomas was first reported by Gobin et al.4) in 8 cases with successful preoperative devascularization. Further depictions of Onyx embolization of meningiomas in the literature are relatively sparse.5)8)9)10)11)13) The purpose of this report was to highlight in detail our experience with Onyx embolization of large or giant extra-axial tumors.

We reviewed our institutional endovascular database for patients undergoing preoperative embolization of extra-axial tumors with Onyx from 2008 to 2014. We extracted patient demographic information such as age and sex, presentation modality, tumor size, tumor location, vascular supply, tumor pathology, technical complications, surgical blood loss and long-term results.

Five patients at our institution underwent preoperative Onyx embolization for extra-axial hypervascular tumors (Table 1). The five cases included four falcine or convexity meningiomas (2 grade I, 1 grade II and 1 grade III) and one hemangiopericytoma (grade II); all tumors were large or giant with middle meningeal artery supply. One case involved Onyx embolization only; the other four tumors were embolized by Onyx along with other agents. Satisfactory devascularization was obtained in all cases as determined by radiographic examination and by both the embolizing and operative physicians. Two patients underwent surgery on the same day of embolization; the remaining three underwent resection on the following day. There were no major complications related to embolization or surgery detected in any of the patients; surgical estimated blood loss ranged from 0.3 to 1.2 liters (median: 0.5 liters).

Onyx is a nonpolymerizing liquid agent composed of ethylene-vinyl alcohol copolymer dissolved in dimethyl sulfoxide. During Onyx injection, the material will precipitate upon contact with aqueous fluid and form a spongy cast that obstructs blood flow. The three principal advantages of Onyx over other glues are its more permanent nature, its better control during release, and lower probability of sticking to the catheter.3)4)5)7) When compared with particles, Onyx is considered to allow for a more controlled injection due to its gradual centripetal precipitation which allows for slower and more accurate injections. The operator may even perform angiographic runs during the Onyx infusion while assessing the progress of the injection.3)4)5)7)

Few published reports of Onyx embolization for meningiomas exist.4)5)8)9)11)13) Some have suggested Onyx should be avoided in tumor embolization because of the high associated cost as well as the large volume required for adequate tumor devascularization.8)9) However, some physicians have reported a preferred use of Onyx especially for the embolization of anterior skull based meningiomas due to collateral tumor supply and the ophthalmic artery. The increased control in Onyx embolization was felt to decrease the chance of embolic material reflux into the central retinal artery.13) One large retrospective study of 100 patients (including 39 meningiomas) with hypervascular head, neck and spinal tumors undergoing Onyx embolization was published recently, demonstrating no major embolization complications.8) Other reports have also demonstrated a lack of significant complications due to Onyx tumor embolization.4)5)9)11)13) Our report reaffirms this low complication rate while providing pictoral evidence of Onyx penetration into the tumor bed (Fig. 1 and Fig. 4). The only major complication linked to Onyx in tumor embolization has been a resultant disseminated intravascular coagulation (DIC) following embolization, although only a hypothesis by the authors.14) Direct tumoral puncture with onyx embolization has also been described as a method.1)3)

While many reasonable embolization agents are available, Onyx was specifically chosen in these hypervascular tumors due to its increased ability to penetrate multiple supplying vessels over repeated injections, thereby increasing the amount of tumor embolized. Particle embolization will only allow penetration of supplying vessels with the highest direct flow. However, slow, controlled, and visualized penetration of the tumor with Onyx will allow occlusion of one territory before recruitment into other vascular territories with increased ease. In addition, the concern that such high flow may allow particle migration to the venous phases during the embolization of the hemangiopericytoma, possibly increasing the risk of venous thrombosis, made us opt for Onyx in that particular case.

Some recent reports have described the delayed resection of embolized tumors without demonstrating increased complication rates.6)8)11) We prefer resection within 24 hours as a means to decrease the likelihood of vascular recruitment around the embolized vessels and also as a cost efficient approach that can even be performed under the same anesthetic for patients undergoing surgery the same day. In addition, potential post-embolization edema is met with swift surgical excision with this more expedient approach, though this was not ostensibly encountered in this series where we demonstrate the success of Onyx embolization of these tumors without associated complications.

Preoperative embolization of extra-axial hypervascular tumors using Onyx is a recent approach in their endovascular adjunctive management. This series augments the expanding literature suggesting the safety and efficacy of Onyx in preoperative tumor embolization, underscoring the value of being able to attain extensive devascularization via only one supplying pedicle.