The SQUID Trial for the Embolization of the Middle Meningeal Artery for Treatment of Chronic Subdural Hematoma (STEM)

Treatment failure as defined by the occurrence of any of the following events:

• Residual or re-accumulation of the SDH (≥10 mm) on 180-day scan from intervention.
• Re-operation (after index procedure) or surgical rescue within 180-days of intervention.
• Any new, major disabling stroke, myocardial infarction (MI) or death from any (neurological) cause within 180-days of intervention.

Major disabling stroke or any death within 30-days from intervention.

Number of participants with an adverse event (AE) or serious adverse event (SAE) adjudicated as probably or causally related to the investigational device or Middle Meningeal Artery Embolization (MMAE) procedure.

The modified Rankin Scale (mRS) is an ordinal scale used to measure the degree of disability or dependence in the daily activities of people who have suffered a stroke. Scores range from 0 (no symptoms) to 6 (death):

0: No symptoms

• No significant disability
• Slight disability
• Moderate disability
• Moderately severe disability
• Severe disability
• Dead The Shift Analysis (also known as an ordinal analysis) evaluates the distribution of mRS scores to identify a general improvement or 'shift' across the entire range of the scale, rather than just comparing 'good' vs. 'poor' outcomes.

The Modified Rankin Scale (mRS) is a clinician-reported measure used to assess the degree of functional disability or dependence in daily activities following a neurological event. This binary outcome dichotomizes the 7-point scale (0-6) into two categories: Favorable Outcome (mRS 0-2) and Unfavorable Outcome (mRS 3-6).

A score of ≤ 2 signifies that the participant is functionally independent and capable of looking after their own affairs without assistance. Results will be reported as the proportion of participants in each treatment arm achieving a score of 0, 1, or 2 at the 180-day follow-up.

T-scores were used to convert raw data to standardized scale with a mean of 50 and a standard deviation of 10. A higher T-score indicates better cognitive performance (a score near 40 indicates a low average to average range). Global neurocognitive performance was assessed by taking the mean T-score for all individual neurocognitive markers (Hopkins Verbal Learning Tests (HVLT-R), Controlled Oral Word Association Test (COWAT), Animal Naming, and Trail making tests).

The EQ VAS is a 20 cm vertical visual analogue scale that records the patient's self-rated health today. It ranges from 0 (Worst health you can imagine) to 100 (Best health you can imagine).

The EQ-5D-5L (EuroQol - 5 Dimension - 5 Level) is a standardized, patient-reported instrument used globally to measure health-related quality of life (HRQoL). It assesses health across 5 dimensions-mobility, self-care, usual activities, pain/discomfort, and anxiety/depression-with 5 levels of severity. The index score ranges from -0.59 to 1.0, where 1.0 represents 'full health' and 0.0 represents death. A higher score indicates a better health-related quality of life. Change is calculated as (180-Day score minus Baseline score)

The number of days (mean) in hospital from baseline through 180 days.

The National Institutes of Health Stroke Scale (NIHSS) is a standardized tool used to objectively quantify the neurological impairment caused by a stroke. It consists of 15 items assessing areas such as level of consciousness, vision, motor function, sensation, and language.

Score Range: Total scores range from 0 to 42. Interpretation: A score of 0 indicates normal function (no symptoms), while higher scores indicate more severe neurological deficit.

This outcome measures the mean change in the total NIHSS score from baseline (at enrollment) to the 90-day follow-up

The total number of ICU days from baseline through 180 days.

Core Lab Analysis of CT/MRI Images. The thickness of the cSDH was documented separately for the left and right sides.