The research, led by Zhuohua Wen, Xiheng Chen, and Xin Tong of Southern Medical University in Guangzhou together with colleagues at several major Chinese hospitals, is a nested analysis within a prospective multicenter cohort known as the SESIA study. Rather than a small retrospective chart review, the investigators drew on a carefully maintained registry of patients undergoing flow diverter implantation for unruptured aneurysms, allowing them to examine outcomes with a degree of rigor rarely achieved in this field. Using propensity-score matching with exact matching on aneurysm location, the team assembled 1327 patients, of whom 360 received glucocorticoids and 967 did not. This statistical technique attempts to balance the two groups on every measurable characteristic, including age, aneurysm size, aneurysm location, and procedural details, so that the only meaningful difference between them is the exposure being studied.

The glucocorticoid regimen itself was strikingly simple. Patients received intravenous glucocorticoids initiated within two hours of the flow diverter procedure and continued for at least two days afterward. The doses were deliberately low, far below the levels typically used to suppress severe autoimmune disease, reflecting the idea that only a modest dampening of the inflammatory cascade was needed to protect the vessel wall during the most vulnerable period after stent deployment. This is not a new drug, not an experimental molecule, and not an expensive biologic; glucocorticoids such as methylprednisolone have been mainstays of medicine for decades and cost only a few dollars per course, making the findings immediately relevant to hospitals in every corner of the world.

The results are dramatic. In the hospital, 6.9 percent of patients who received glucocorticoids experienced a cerebrovascular event, compared with 13.1 percent of those who did not, an adjusted odds ratio of 0.53. When the investigators focused on major cerebrovascular events, the most serious complications such as disabling strokes, the difference was even more pronounced: 4.7 percent in the glucocorticoid group versus 12.4 percent in the control group, an adjusted odds ratio of 0.37, meaning the treatment was associated with nearly a two-thirds reduction in the odds of these severe outcomes. In practical terms, for every hundred patients treated with a flow diverter, the addition of a short glucocorticoid course could prevent roughly seven major cerebrovascular events that would otherwise occur during the hospital stay.

The benefits did not stop when patients left the hospital. Over a median follow-up of two years, the glucocorticoid group experienced fewer new-onset major cerebrovascular events, 3.6 percent versus 8.7 percent, with an adjusted hazard ratio of 0.41. The investigators also examined the stents themselves using imaging and found significantly less in-stent stenosis, the narrowing that occurs when scar tissue and inflammation build up inside the device and restrict blood flow through the parent artery. In-stent stenosis occurred in 7.9 percent of glucocorticoid-treated patients compared with 13.2 percent of controls, an adjusted odds ratio of 0.55. This finding is particularly important because in-stent stenosis is not merely a technical concern; it can compromise the long-term patency of the vessel, reduce blood flow to downstream brain regions, and in some cases necessitate additional procedures or antiplatelet therapy adjustments.

The biological rationale for these findings is grounded in the inflammatory response that follows endovascular device implantation. When a flow diverter is deployed, the metallic mesh comes into contact with the vessel wall, activating platelets, complement proteins, and leukocytes. Inflammatory cells infiltrate the vessel wall, releasing cytokines and proteases that promote both thrombus formation on the device surface and smooth muscle cell proliferation within the arterial wall. Glucocorticoids bind to intracellular receptors that translocate to the nucleus and suppress the transcription of pro-inflammatory genes, including those encoding tumor necrosis factor and interleukins, while promoting the resolution of inflammation through the upregulation of anti-inflammatory mediators such as annexin A1. By tempering this cascade during the critical perioperative window, a short course of low-dose steroids may prevent the initial inflammatory trigger from escalating into clinically significant thrombosis or stenosis.

The investigators were careful to test the robustness of their findings. Sensitivity analyses in unmatched patients, meaning the full cohort without propensity-score balancing, confirmed the same direction of effect, suggesting that the results are not an artifact of the matching procedure. The team also used adjusted models that accounted for residual confounding, and the findings remained consistent across multiple statistical approaches. Still, the authors are appropriately cautious in their interpretation. This is an observational analysis, not a randomized controlled trial, and it is possible that unmeasured differences between patients who received glucocorticoids and those who did not could have influenced the outcomes. The appropriate conclusion, as the authors state, is that perioperative glucocorticoid regimens warrant testing in randomized trials, not that every flow diverter patient should immediately receive steroids.

Nevertheless, the implications are significant. Flow diverter therapy has become the standard of care for many unruptured intracranial aneurysms, and the procedure is performed in tens of thousands of patients worldwide each year. Cerebrovascular complications after flow diverter implantation remain a major source of morbidity, and current strategies rely primarily on dual antiplatelet therapy with aspirin and a P2Y12 inhibitor such as clopidogrel or ticagrelor. Antiplatelet drugs address clot formation but do nothing to suppress the inflammatory response that drives vessel wall thickening and in-stent stenosis. Glucocorticoids, by contrast, target the inflammatory arm of the response, potentially complementing antiplatelet therapy in a way that no existing drug currently does. If randomized trials confirm these findings, a short course of low-dose intravenous steroids could become a routine adjunct to flow diverter procedures, adding only a few dollars to the cost of a treatment that already costs tens of thousands of dollars.

The study also highlights a broader lesson for modern medicine. Some of the most impactful advances in patient care come not from novel molecules but from rethinking how existing, inexpensive drugs are used in new clinical contexts. Glucocorticoids have been available since the mid-twentieth century, yet their precise timing, dosing, and duration in the setting of endovascular neurosurgery had never been systematically examined in a large prospective cohort. The SESIA investigators demonstrated that a rigorous observational analysis can identify a signal strong enough to justify randomized testing, potentially accelerating the path to improved patient outcomes without waiting for the decade-long development cycle of a new drug. For patients facing flow diverter therapy for an unruptured brain aneurysm, the prospect of a simple, cheap, and short steroid course that could cut the risk of disabling stroke by more than half is a finding that deserves the attention of every neurosurgeon, neurologist, and intensivist who cares for these patients.

Subject of Research: Low-Dose Glucocorticoids Adjunctive to Flow Diverter Therapy for Unruptured Intracranial Aneurysms Improve Cerebrovascular Outcomes

Article Title: Low-Dose Glucocorticoids Adjunctive to Flow Diverter Therapy for Unruptured Intracranial Aneurysms Improve Cerebrovascular Outcomes

Article References: Wen, Z., Chen, X., Tong, X., Huang, C., Huang, M., Lin, J., Xu, A., Yang, H., Zhang, X., Lin, Y., Huang, J., Ge, R., Yuan, H., Peng, C., Liu, Y., Jin, F., Su, S., Zhang, X., Li, X., … Feng, X. (2026). Low-Dose Glucocorticoids Adjunctive to Flow Diverter Therapy for Unruptured Intracranial Aneurysms Improve Cerebrovascular Outcomes. Nature Communications. https://doi.org/10.1038/s41467-026-78408-w

Image Credits: AI Generated

DOI: 10.1038/s41467-026-78408-w

Keywords: Low-Dose, Glucocorticoids, Adjunctive, Flow, Diverter, Therapy, Unruptured, Intracranial, Aneurysms, Improve, Cerebrovascular, Outcomes

Moyamoya disease is a chronic, progressive occlusion of the terminal internal carotid arteries and their proximal branches, characterised by the development of a fragile network of compensatory collateral vessels at the base of the brain that resembles a puff of smoke on angiographic imaging. When medical therapy alone cannot prevent recurrent ischemic or hemorrhagic events, surgeons turn to revascularization procedures. Indirect bypass, the technique central to the Chen study, involves laying vascularised tissue such as the temporalis muscle directly onto the cortical surface, relying on the patient’s own biological capacity to sprout new arteries from the donor tissue into the ischemic brain over weeks to months. The molecular signals that govern this neoangiogenesis have remained poorly characterised, which is precisely why the transcriptomic profiling approach attracted so much attention.

The Chen team’s central finding was that genes associated with extracellular matrix organisation and collagen deposition were significantly enriched in patients who went on to develop robust collateral circulation after surgery, as graded by the Matsushima angiographic scale. This suggested that the structural scaffold laid down by the transplanted temporal muscle might serve as a permissive microenvironment through which endothelial cells migrate, proliferate, and anastomose with the cortical vasculature. The implication was tantalising: if collagen-rich matrix remodelling is a driver rather than a byproduct of successful collateralisation, then pharmacological modulation of matrix biology could one day enhance surgical outcomes in patients whose native angiogenic response is insufficient.

However, Rani and Baig argue that this conclusion rests on a cohort whose internal heterogeneity was never adequately controlled. Their first and most pointed criticism concerns the pooling of paediatric and adult patients without stratification by clinical disease stage, whether measured by the Suzuki angiographic staging system or by hemodynamic assessment of cerebral perfusion reserve. Children with Moyamoya disease possess a dramatically higher native capacity for neoangiogenesis and collateral development than adults, a biological trait that operates independently of any measurable difference in extracellular matrix gene expression. When these two age groups are analysed together, the resulting transcriptomic signature may simply reflect an age-specific baseline angiogenic response rather than a shared molecular mechanism of surgical success.

The letter elaborates on this confounding problem with technical precision. Endogenously generated differential angiogenic signals are themselves associated with advanced disease stage and severe basal hypoperfusion, meaning that the ischemic drive within the brain tissue of a stage IV patient is fundamentally different from that of a stage II patient. Without correcting multi-variable transcriptomic models for pre-operative Suzuki staging and cerebrovascular reserve capacity, the collagen-rich signature identified by Chen and colleagues could be an artifact of mixed disease severity rather than a genuine molecular predictor of collateral formation. Rani and Baig point to prior work by Bao and colleagues, published in Frontiers in Neurology, which demonstrated that the efficacy of indirect revascularization is intrinsic to an exquisite balance between disease stage progression and age-associated neoangiogenic potential, with different patient subsets exhibiting markedly different collateral formation trajectories.

The second major objection concerns the absence of a surgical comparator group. The Chen study included only patients who underwent indirect bypass, with no tissue samples from individuals who received direct bypass procedures, such as superficial temporal artery to middle cerebral artery anastomosis, or combined approaches that pair direct bypass with encephaloduroarteriomyosynangiosis. This distinction is not merely academic. Direct bypass restores hemodynamic function immediately by creating a high-flow surgical connection between extracranial and intracranial circulation, fundamentally altering shear stress and metabolic conditions in the adjacent cortical tissue from the moment the clips are released. Indirect bypass, by contrast, depends entirely on tissue-level angiogenesis unfolding over an extended postoperative period. The molecular programs activated in temporal muscle under these two radically different hemodynamic regimes are unlikely to be identical, yet without comparative tissue from combined or direct bypass patients, the Chen results cannot be generalised across surgical techniques.

Rani and Baig reference a retrospective study by Zhao and colleagues published in Experimental and Therapeutic Medicine, which examined 76 combined direct and indirect bypass procedures in adult Moyamoya patients and found significantly different clinical and angiographic outcomes compared to standalone indirect procedures, along with distinct local tissue perfusion pressures. They argue that the addition of tissue controls from patients undergoing combined direct-indirect bypass would allow future transcriptomic studies to separate expression patterns of extracellular matrix molecules that are specific to the indirect angiogenic process from those that merely reflect general tissue healing under different flow conditions. This is a critical distinction for any researcher hoping to translate collagen biology into a therapeutic target, because a signature that appears in all postoperative temporal muscle regardless of surgical approach is unlikely to be the molecular key to collateral vessel formation.

The third concern addresses clinical phenotyping, or rather the lack thereof. The Chen study grouped patients into binary collateral outcomes using the Matsushima grading system but did not account for the primary clinical presentation, namely whether patients presented with ischemic or hemorrhagic Moyamoya disease. These two phenotypes are not interchangeable variants of the same illness. Ischemic and hemorrhagic Moyamoya differ in their underlying pathophysiological mechanisms, in the degree of vessel wall inflammation, and in the postoperative trajectory of collateral formation. Hemorrhagic Moyamoya is characterised by microvascular fragility and altered expression of matrix metalloproteinases, enzymes that directly degrade extracellular matrix components and are intimately connected to temporal muscle tissue biology and postoperative angiogenesis. The unchecked accumulation of both phenotypes within a single transcriptomic cohort risks blending phenotype-specific molecular drivers of collateralisation into an averaged signal that corresponds to neither group.

Rani and Baig cite work by Ge and colleagues published in BMC Neurology, which specifically examined postoperative collateral formation after indirect bypass in hemorrhagic Moyamoya disease and found that collateral dynamics and angiographic response differ according to aetiology. They call for subgroup analyses of ischemic and hemorrhagic patients to determine whether the collagen-rich extracellular matrix signature identified by Chen and colleagues is preserved across both presentations or whether it is a molecular fingerprint unique to one phenotype. If the signature diverges between ischemic and hemorrhagic Moyamoya, then any future therapeutic strategy aimed at enhancing matrix remodelling would need to be tailored to the specific clinical context, a level of precision that the current mixed-cohort analysis simply cannot support.

In their concluding remarks, Rani and Baig strike a constructive tone, acknowledging that Chen and colleagues have provided a much-needed molecular underpinning of the relationship between extracellular matrix remodelling, collagen deposition in temporal muscle tissue, and successful postoperative collateralisation in Moyamoya disease. They emphasise, however, that angiogenic potential, disease stage, surgical approach variability, and clinical phenotype remain critical variables that must be addressed before these transcriptomic discoveries can be translated into targeted therapeutic tools. Their prescription is clear: multi-centre, phenotype-stratified, prospective cohorts with age-matched paediatric and adult subgroups, corrected for pre-operative Suzuki staging and cerebrovascular reserve, and including tissue comparators from direct and combined bypass procedures. Only through such rigorous design, they argue, can the field determine whether collagen-rich extracellular matrix biology is a genuine driver of collateral vessel formation or a molecular echo of patient heterogeneity.

Subject of Research: Moyamoya disease transcriptomics and postoperative angiogenesis

Article Title: Letter to Editor on Collagen‐Rich Extracellular Matrix and Postoperative Angiogenesis in Moyamoya Disease: The Need for Phenotype‐Stratified Transcriptomic Analysis

Article References: Rani, E., & Baig, M. F. (2026). Letter to Editor on Collagen‐Rich Extracellular Matrix and Postoperative Angiogenesis in Moyamoya Disease: The Need for Phenotype‐Stratified Transcriptomic Analysis. Journal of Cellular and Molecular Medicine, 30(19), Article e71400. https://doi.org/10.1111/jcmm.71400

Image Credits: AI Generated

DOI: 10.1111/jcmm.71400

Keywords: Moyamoya disease, transcriptomics, collagen, extracellular matrix, angiogenesis, revascularization, cerebrovascular, letter to editor, Letter, Editor, Rich, Extracellular