Recently presented results from the STEM randomised controlled trial (RCT) have demonstrated improved outcomes with middle meningeal artery (MMA) embolisation plus standard management—as compared to standard management alone—in patients with chronic subdural haematoma (cSDH).
At the 2024 International Stroke Conference (ISC; 7–9 February, Phoenix, USA), Adam Arthur (University of Tennessee Health Science Center, Memphis, USA)—co-principal investigator for STEM alongside David Fiorella (Stony Brook Cerebrovascular Center, Stony Brook, USA)—relayed that MMA embolisation with the Squid liquid embolic system (Balt) was deemed superior to standard management on the basis of the study’s primary effectiveness endpoint, and produced acceptable safety outcomes as well.
Arthur began by noting that standard management strategies for cSDH patients not requiring emergent surgical evacuation include medical management, often involving observation and/or drug therapies, and procedures like craniotomies or burr-hole surgeries. However, he continued, practice patterns in this space “vary widely”, and “substantial failure rates” have been reported with both surgical and non-surgical management approaches.
Over the past few years, interest has grown in MMA embolisation involving liquid embolic agents, leading to a multitude of RCTs—including EMBOLISE, MAGIC-MT, and STEM—being set up to evaluate their performance in non-acute SDH patients. Late-breaking data from all three of these studies were presented at ISC 2024.
STEM set out to assess the Squid liquid embolic system—a device that gained CE-mark approval in 2012 but is currently limited to investigational use only in the USA—as an adjunct to surgical or non-surgical SDH management. The international, multicentre, prospective pivotal trial saw a total of 310 patients allocated to either surgical management (n=189) or non-surgical management (n=121) for their cSDH, with patients in each group then being randomised to MMA embolisation plus their allocated medical management strategy (treatment arms), or their allocated medical management strategy only (control arms).
The trial was powered to ascertain the comparative effectiveness and safety of MMA embolisation plus standard management against that of standard management alone. As per STEM’s primary effectiveness endpoint, there were three distinct modes of failure in the trial: residual or reaccumulated SDH (≥10 mm) at 180 days post-intervention; reoperation after index procedure or surgical rescue within 180 days of randomisation; and a new, major disabling stroke, myocardial infarction or death from any neurological cause within 180 days of randomisation. The trial’s primary safety endpoint pertained to any major disabling stroke or death within 30 days post-intervention.
Arthur reported that enrolment in the study took place between November 2020 and May 2023, with the final six-month follow-up being completed in December 2023, and one-year follow-up assessments currently still ongoing across 25 US sites as well as a handful of European centres. An average age of 73.2 years (range, 39–97) and a 69.6% rate of male gender were present throughout the 310-patient population in STEM.
Arriving at the trial’s key primary-endpoint finding, Arthur presented preliminary results indicating a failure rate of 39.2% with standard management, compared to 15.2% with MMA embolisation plus standard management—data ultimately associated with an odds ratio (OR) of 3.6 (p=0.0001) favouring the latter treatment approach. According to Arthur, this discrepancy was more pronounced when comparing MMA embolisation against non-surgical management for cSDH. Subgroup analyses revealed a failure rate of 59.2% with non-surgical management alone versus 19.1% with MMA embolisation plus non-surgical management (OR, 6.1; p=0.0001), while failure rates for surgery alone and MMA embolisation plus surgery were 25.4% and 12.3%, respectively (OR, 2.4; p=0.058).
Moving on to deliver 30-day safety outcomes in STEM, the presenter reported similar rates of all-cause mortality across the two main study arms, with four deaths in the treatment arm (rate, 2.7%) and five in the control arm (rate, 3.1%). He also emphasised that none of the deaths in the treatment arm were attributed to MMA embolisation or the Squid system itself. The occurrence of major disabling stroke was comparable between the two as well, with zero being observed in the treatment arm and one observed in the control arm (rate, 0.6%).
Following his conveyance of these preliminary findings, Arthur concluded by stating that he is “very interested” in the future presentation of additional endpoints from STEM—including data on modified Rankin scale (mRS) shift analyses, cognitive impairment and quality-of-life changes versus baseline, and hospital length of stay.
