The Source for Neurovascular News and Education

November 29, 2022


Key Points:

  • Study compares outcomes of cerebral AVMs embolized with Onyx, NBCA
  • No significant differences in periprocedural outcomes between the 2 treatments 


Outcomes of endovascular treatment for cerebral arteriovenous malformations (AVMs) have held steady before and after the introduction of Onyx into clinical practice, according to a paper published in the Journal of Neurosurgery.

 For the retrospective study, Cameron G. McDougall, MD, of the Barrow Neurological Institute (Phoenix, AZ), and colleagues reviewed data on 342 cerebral AVMs that were treated during 446 sessions at their center between 1995 and 2012. Most AVMs were embolized in 1 session (76%) or 2 sessions (19%), with a maximum number of 4 sessions (< 1%). 


The Take Home

“[R]egardless of the embolic agent employed, it is likely that complication rates will vary with treatment objectives, operator experience, and operator perception of risk-to-benefit ratio,” researchers say.


Wide Variety of Clinical Presentations, UsesOverall, Onyx (Covidien)—a nonadhesive liquid embolic agent used for presurgical embolization of AVMs approved by the FDA in 2005—was used in 30.7% of AVMs and N-butyl cyanoacrylate (NBCA) without Onyx in 67%, while 11.4% of cases involved both treatments.

Clinical presentation included hemorrhage (47.6%), seizure (21.9%), headache (11.1%), and no symptoms (10%). Endovascular pretreatment was preoperative in 78.9% of cases. Other cases were pre-radiosurgery (9.1%), palliative (5.3%), targeted (4.4%), and curative (2.3%). Median Spetzler-Martin grade was III.

After the procedures, unexpected and immediate neurological morbidity or mortality affected 11.4% of AVMs; deficits were permanent in 9.6% and transient in 1.8%. One periprocedural death occurred (0.3%), and clinically silent procedural complications were observed in 7.6% of patients.

Surgical risk was not associated with outcome; permanent neurological differences occurred in 12%, 9%, 13%, 11%, and 13% of AVMs classified as Spetzler-Martin grades I through V, respectively (P = .91). Patient sex also was not related to outcome.

Outcomes Similar Between Treatment Approaches

Mean patient age was lower in the Onyx group (34.6 vs 39.3 years; P < .05), though there were no other baseline differences. Cases involving Onyx had a higher number of arterial pedicles embolized than did NBCA cases (mean 4.3 vs 3.2; P < .001) and a greater number of sessions (mean 1.5 vs 1.2; P < .05).

Outcomes were similar for the 2 treatments, even when adjusted for the number of sessions and arteries (table 1).

Table 1. Outcomes of AVM Treatment




P Value

Adjusted P Value

Unexpected Periprocedural Neurological Morbidity





Unexpected Permanent Morbidity





Silent Complications





Total Complications





While most studies have shown NBCA and Onyx to be equivalent, the investigators say, a single-center experience published in 2013 suggested that Onyx might be associated with functional impairment, though the difference was not statistically significant. “The authors [of that paper] conclude that the introduction of Onyx has not improved outcomes, and may embolden the neurosurgeon by giving a false sense of protection from complications,” they write, noting that no data were presented on complications.

“It is important to appreciate that, regardless of the embolic agent employed, it is likely that complication rates will vary with treatment objectives, operator experience, and operator perception of risk-to-benefit ratio,” Dr. McDougall and colleagues explain.

Based on the current study, they say, it appears that choice of NBCA vs Onyx has no bearing on complications. “This raises the question of what other factors are therefore important in making the choice between the embolic agents, and highlights the difficulties inherent in evaluating the effectiveness of embolization,” the researchers comment. Such evaluation differs when the goal of treatment is cure or facilitation of resection, they add.

In an editorial accompanying the paper, Gregory J. Zipfel, MD, of Washington University School of Medicine (St. Louis, MO), points out that Dr. McDougall and colleagues did not evaluate efficacy, a drawback the researchers themselves acknowledge. “Therefore, future studies will be needed to objectively compare the angiographic outcome of Onyx vs NBCA embolization, which if proven superior would suggest that the balance of risk vs efficacy may ultimately favor the use of Onyx as the primary embolization technology of cerebral AVMs,” he writes.

Data Demonstrate the Power of Experience

According to Alejandro Berenstein, MD, of Mount Sinai Hospital (New York, NY), the main message of the study, which was done at a well-known center, is that experience matters.

“If you are properly trained, [Onyx] is an excellent addition to the treatment of AVMs,” he said in a telephone interview with WLNCMD, noting that outcomes will differ between clinicians using Onyx 5 times per year and those using it 5 times per month.

Because Onyx is often used prior to surgery, Dr. Berenstein advised, it is crucial for the person performing the embolization to communicate and plan with the surgical team. “If used presurgery, risks should be extremely low because it’s only an adjunctive treatment,” he added.




1. Crowley RW, Ducruet AF, Kalani MYS, et al. Neurological morbidity and mortality associated with the endovascular treatment of cerebral arteriovenous malformations before and during the Onyx era. J Neurosurg. 2015;122:1492-1497.

2. Zipfel GJ. Arteriovenous malformations and embolization. J Neurosurg. 2015;122:1490-1491.



  • Dr. McDougall reports having served as a consultant to Covidien (eV3) and Terumo (Microvention).
  • Drs. Zipfel and Berenstein report no relevant conflicts of interest.