Safety and Clinical Efficacy of Onyx for Embolization of Extracranial Head and Neck Vascular Anomalies

Discussion

Extensive craniofacial AVMs are especially difficult to manage because of disfigurement, functional impairment, and risk of life-threatening hemorrhage.^12–15 It is often impossible to achieve a satisfactory therapeutic result in a single treatment session. Management is often complicated by prior failed treatment attempts, most frequently termination of attempted resection in the past because of uncontrollable intraoperative hemorrhage.¹⁶ Because of the rarity of the craniofacial AVMs and the relative lack of understanding of their pathogenesis,¹⁵ no standard treatment has been established. As a result, various interventional options and treatment algorithms have been proposed.¹³ Although there have been reports of embolization therapy alone achieving successful results in selected cases with smaller craniofacial AVMs, the outcome is usually palliation rather than “cure” for large lesions.^17,18 Some authors have proposed a management algorithm for large craniofacial AVMs, chiefly involving preoperative embolization with n-BCA and PVA several days before resection,¹⁸ resulting in control of large craniofacial AVMs with acceptable esthetic results.

Arat et al⁸ reported the largest series to date by using Onyx as a primary or preoperative embolization agent. There were 9 patients in their series: 3 with craniofacial AVMs and 6 with AVFs. They were successful in treating all AVFs by using Onyx as the primary embolization agent; however, the outcome was less favorable for the 3 patients with AVMs.

One reported major difficulty encountered was reflux of Onyx over the microcatheter,⁸ also reported as a significant technical problem for embolization of intracranial AVMs. Onyx reflux results in difficult retrieval of the microcatheter, potentially resulting in vessel dissection or rupture, or shearing of the distal microcatheter segment. In our experience, the difficulty with proximal reflux of Onyx could be ameliorated by using the plug and push injection method. The Onyx plug formed in the initial injection not only acted as a physical barrier to prevent any significant proximal reflux during the subsequent injections but also promoted distal nidal penetration by increased proximal resistance in the feeding artery.

We achieved complete embolization in only 4 patients, with AVFs (n = 2), facial artery laceration (n = 1), and a maxillary AVM (n = 1), with a single stage of Onyx embolization because of a well-defined fistulous point or nidus isolated to 1 single compartment of the head and neck.

In contrast, because of their complexity, craniofacial AVMs require multiple staged embolizations to reduce the risk of excessive exposure to radiation, intravenous contrast, and Onyx, in 1 single session, with the number of stages required depending on the age of the patient and the size and complexity of the lesion. We targeted the most symptomatic region initially and, in almost all instances, waited at least 4 weeks between each session to allow the DMSO to clear. We typically limit the contrast dose to 4 mL/kg body weight in elective cases (≤7 ml/kg for urgent cases), radiation exposure is limited to 1 Gy per session for elective cases, and maximum Onyx dosage is, as recommended by the manufacturer, ∼1 mL per 10 pounds (4.54 kg) of body weight.

Proximal embolization of feeding arteries of any AVM is contraindicated because it promotes recruitment of nearby arteries to supply the lesion and limits any future endovascular access to the nidus.¹⁹ It is important to carefully position the microcatheter tip distally to avoid proximal arterial ligation in multistaged embolizations.

Given its dark color, superficial Onyx embolization, and especially subcutaneous extravasation, can cause blackish discoloration of the skin.⁸ We did not encounter cutaneous necrosis or marked discoloration in any patient. When Onyx is used preoperatively to reduce blood loss, the surgeon should be aware that sparks may result if the material comes in contact with monopolar electrocautery. We have not found this to be problematic, and our surgical colleagues continue to use electrocautery during resection in Onyx cases.

The results of using Onyx for embolization of craniofacial AVMs in a multistaged fashion are promising. Immediate postembolization angiography showed successful reduction in the nidal size. Subsequent angiography demonstrated that areas embolized in the previous stage remained occluded, without recanalization or re-expansion of the lesion.

While some authors have suggested the best therapeutic result is achieved for treatment of a craniofacial AVM by combined preoperative embolization with surgery, a “total cure” for an extensive craniofacial AVM may not be achievable because of the extensive area covered and viable structures involved.¹⁴ Instead, in patients in whom a complete cure is not possible, the therapeutic goal should be tailored to the patient's expectations, which may emphasize the best cosmetic results achievable and effective long-term symptomatic control. Multistaged embolization can also serve as presurgical devascularization, whether or not the ultimate goal of resection was a total cure.

Gomes¹⁷ described alternate approaches to malformations in which transarterial access is limited due to prior surgical ligation or embolization or in fast-flow lesions with a large venous component.^17,20 We used percutaneous cannulation and embolization with Onyx in 4 procedures, with excellent results in all 4 cases, and no evidence of skin discoloration.

We did not encounter nontarget embolization or pulmonary complications following Onyx embolization. In fast-flow shunts, we used coils to form the initial meshwork through which the column of Onyx advanced, thereby lowering the risk of inadvertent venous migration (cases 6, 12, and 20). Local reactions to Onyx, in the form of swelling, local tenderness, or numbness, followed 7 procedures, requiring corticosteroid therapy in 1 patient; all completely resolved within days. As mentioned previously, stretching of a coil occurred in 1 patient; Niemann et al²¹ reported coil stretching in 0.7% of coil embolizations.

The recurrence rate of AVM symptoms and signs after Onyx embolization is unknown. A recent report by Liu et al²² documents near-universal (98%) recurrence in patients with extracranial AVMs after embolization with agents other than Onyx (with an 81% recurrence rate after resection). Whether Onyx embolization will result in a lower recurrence rate remains to be determined with intermediate and long-term follow-up studies.

In summary, our experience by using Onyx for extracranial vascular anomalies shows promising results, particularly for extensive complex craniofacial AVMs. Staged embolizations with Onyx were safe and clinically effective. The permanence of the results in this cohort remains to be determined.