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The presentation of data from multiple large, randomised clinical trials over the past two years has seen middle meningeal artery embolisation (MMAe) emerge as a safe and effective adjunct to surgical drainage in chronic subdural haematoma (cSDH) management—with the Onyx™ liquid embolic system (LES; Medtronic) being the agent of choice in several of these studies. And, more recently, the introduction of the lower-viscosity Onyx 12 LES has expanded the potential armamentarium of neurointerventionists treating cSDH in Europe even further. Here, NeuroNews speaks to two physicians who are at the precipice of this ongoing shift in neurovascular care.
EMMA-Can—one of the aforementioned trials to have substantiated MMAe’s benefits—was conducted across nine Canadian tertiary care centres, randomising 192 adults with symptomatic, unilateral cSDH measuring at least 10mm in axial thickness who were undergoing surgical drainage. These patients were randomised to either surgical drainage alone or surgical drainage followed by MMAe within 72 hours of surgery using Onyx 18 LES. The primary efficacy endpoint was symptomatic cSDH recurrence detected on computed tomography (CT) at 90 days, with safety outcomes assessed separately.1
“The trial demonstrated a substantial reduction in symptomatic recurrence following adjunctive MMAe,” relays EMMA-Can principal investigator Jai Shankar (University of Manitoba, Winnipeg, Canada). “The primary endpoint occurred in just 4.3% of patients in the MMAe arm compared to 28% in those who received surgery alone. This represents an absolute risk reduction of 23.7%. And, based on this risk reduction, the number needed to treat [NNT] was 4.2, which suggests a very clinically meaningful treatment effect.”
Touching on the trial’s key secondary endpoints, Shankar also notes that radiographic haematoma recurrence was observed in 49.5% of surgical patients versus 14% of MMAe patients—with the NNT for this metric being closer to three—while rates of overall mortality and serious adverse events were statistically similar between the two groups.
“I have to say that [the NNT] was a pleasant surprise to our team—we were expecting it to be positive, but we did not expect the NNT to be that low,” he adds. “In neurosurgery and neurology worlds, an NNT of three or four is not very common. The NNT for thrombectomy in acute ischaemic stroke is around four, so we are reaching that threshold. Moving forward, the challenge—as with thrombectomy—will be implementing this highly effective treatment into routine clinical practice; but, given the evidence is now there, healthcare systems should move to incorporate this treatment over the next few years.”
A distinct design
While other randomised trials have produced positive findings on MMAe—including EMBOLISE, MAGIC-MT and OTEMACS utilising Onyx, as well as studies like STEM and MEMBRANE that evaluated alternative embolic agents—the NNT seen in EMMA-Can is the lowest figure achieved in any such trial to date. When asked about notable differences that distinguish EMMA-Can from these trials, Shankar first highlights the omission of repeat surgery from EMMA-Can’s primary endpoint owing to this outcome measure being multifactorial and “highly subjective”, as well as the pragmatic nature of EMMA-Can’s patient population, adding: “We feel our trial has a more applicable and more generalisable inclusion criteria compared to others.”
Additionally, EMMA-Can was an open-label trial with blinded-endpoint adjudication, with randomisation occurring only after surgical drainage, maintaining blinding of the operating surgeons during the procedure and reducing the potential for treatment allocation to influence surgical completeness. Shankar also cites the fact that the significance of distal penetration during embolisation was emphasised a priori as part of the trial’s methodology.
“The last point is that we only lost one patient to complete follow-up,” Shankar comments. “Loss to follow-up is a very important aspect of any study, and ours was just 0.5%, [minimising the potential for bias from missing data and strengthening confidence in the findings].”
“This is definitely an exciting time for innovation in cSDH care,” he continues. “We feel that adding MMAe to surgery will reduce repeat operations, shorten hospital stays, decrease healthcare costs and, overall, improve patients’ quality of life. We have to understand that not everything was proven in EMMA-Can—but secondary analyses are now also showing that adjunctive MMAe hastens the rate of resorption, as per [significantly greater reductions in] haematoma thickness and volume at 90 days, which is very important.”
Control, visibility and speed
In addition to the wealth of recent data on the positive outcomes that can be achieved using established iterations of the Onyx LES, European physicians treating cSDH received another boost earlier this year with the launch of Onyx 12—a lower-viscosity agent that “completes” the Onyx product family.
So says Ansgar Berlis (University Hospital Augsburg, Augsburg, Germany), who was among the first physicians to begin utilising this new LES following its recent CE-mark approval. He explains that having this lower viscosity, alongside Onyx 12’s “very good” reflux control, is critical in facilitating precise and distal penetration of the embolic material—for cSDH in particular, but also for arteriovenous malformations (AVMs), dural arteriovenous fistulas (dAVFs) and brain tumours.
“The visibility is perfect, allowing the safe and secure injection of the embolic material, and its behaviour is really nice and compares favourably to other low-viscosity embolic agents,” Berlis adds.
To illustrate these points, he highlights two noteworthy examples from the handful of cases he has completed since Onyx 12 arrived at his centre: a tentorial dAVF treatment in which it provided the precise control he needed in order to stop embolising immediately after filling a single venous pouch, and a challenging brain AVM in which—despite the AVM having undergone eight prior embolisation procedures—Onyx 12 remained fully visible upon injection. Berlis recalls that the latter of these observations was “absolutely astonishing” to him.
“While you can combine different DMSO [dimethyl sulfoxide]-based embolic agents, most of my colleagues only want to use one material to treat AVMs and cSDHs,” he also states. “Therefore, it’s important to have all of these different viscosities within one product family; you can start with Onyx 20 or 18, and, if you need more [distal] penetration, you can go ahead with Onyx 12.”
Even with all these positive traits in mind, however, Berlis feels the greatest benefit introduced by Onyx 12 is its one-minute shake time—a marked decrease from preparation times of
15–20 minutes recommended for other tantalum-based products.
“It’s a really big advantage that the preparation time is so fast,” he avers. “If the tantalum powder and the embolisation material are not properly mixed, you may have reduced visibility during the injection, which is very dangerous. That’s why a short preprocedural shake time is so important—especially if you need it very quickly, such as when the patient has acute bleeding. Previously, we would have to use glue or coils in these situations, but—with this one-minute shake time—liquid embolics are now available for more indications.”
“The reflux control, [distal] penetration and visibility are really good but, if you look at all the available EVOH [ethylene vinyl alcohol]-based liquid embolics with a lower viscosity, the short preparation time is what makes the difference,” Berlis concludes. “For me, the introduction of Onyx 12 is a very important step. My initial experience has been really good, and—because I’m so happy and confident with it—I see Onyx 12 becoming a routine part of my clinical practice.”
References:
- Shankar J, Alcock S, Kashani N et al. Management of chronic subdural hematoma with adjunctive embolization of middle meningeal artery: the EMMA-Can randomized clinical trial. JAMA. 2026; 335(20): e264965.
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