Decompressive Craniectomy After Aneurysmal Subarachnoid Hemorrhage (DECIDE-SAH)

Decompressive craniectomy is used in selected patients with aneurysmal subarachnoid hemorrhage (aSAH) to manage space-occupying hemorrhage, cerebral edema, infarction-related swelling, or refractory intracranial hypertension. Existing evidence is predominantly observational and heterogeneous and is strongly affected by confounding by indication, differences in baseline severity, treatment timing, technical characteristics, center-specific practice, and treatment-era effects. DECIDE-SAH is an international, multicenter, retrospective, observational, non-interventional secondary-use patient-level cohort study using pre-existing routine-care data. There is no randomization, prospective treatment allocation, study-specific diagnostic or therapeutic procedure, investigational product, or study-related patient contact. Clinical management was determined independently by the treating teams. Only routine-care information documented on or before 15 September 2026 is eligible for the study dataset under the current protocol. The study uses a hierarchical data architecture consisting of a Minimum Required Dataset (MRD), a Standard Dataset, and optional Extension Modules. The MRD is the minimum information required for scientifically interpretable cohort contribution and includes a technical center-specific study identifier without direct identifiers, an index time period for the qualifying aSAH episode, age, sex, initial clinical severity, aneurysm-treatment status and modality, decompressive-craniectomy status, and at least one interpretable discharge clinical outcome. Complete Standard Dataset or Extension Module information is not required for cohort eligibility. Six-month mRS is required for the registered primary endpoint analysis but is not required for participation in analyses that use other available outcomes. DECIDE-SAH is availability-based and does not use a fixed prospective recruitment target derived from a power calculation. Each participating center is expected to contribute the largest reliably available consecutive eligible adult aSAH cohort from its authorized retrospective source-data period rather than selected decompressive-craniectomy cases only. There is no minimum center case count and no requirement for identical calendar periods across centers. Centers with low or no routine use of decompressive craniectomy remain eligible because between-center practice variation is an important component of the observational study framework. The principal exposure is decompressive craniectomy during the index hospitalization. Exact or best-available ictus-to-DC timing and the clinical context at the treatment decision are prioritized where available. The contributing center/source classification of Primary DC versus Secondary DC is retained as a pragmatic exposure variable and is not defined by a fixed ictus-to-DC hour threshold. For Primary DC, the relevant clinical context is the baseline/admission or intraoperative status; for Secondary DC, pre-Secondary-DC neurological status is used where available. The documented indication and technical characteristics of DC, including type, extent or dimensions where available, duraplasty, and concomitant procedures, are also considered. Descriptive any-DC versus no-DC comparisons may be reported, but clinically comparable treatment-strategy analyses will be defined according to the available temporal and clinical granularity. The primary endpoint is unfavorable functional outcome approximately 6 months after ictus, defined as modified Rankin Scale (mRS) 4-6. Routine-care assessments obtained within 3 to 9 months after ictus are eligible; when more than one assessment is available, the assessment closest to day 180 is selected, and if two assessments are equally close, the later assessment is used. Secondary outcomes include ordinal and alternative dichotomized mRS outcomes, discharge outcome, mortality, mRS at approximately 12 and 24 months where retrospectively available, cerebral infarction, delayed cerebral ischemia-related infarction, rebleeding before aneurysm treatment, intracranial-hypertension burden, hydrocephalus and ventriculoperitoneal shunt placement, endovascular rescue treatment for vasospasm or delayed cerebral ischemia, intensive-care and hospital length of stay, and decompressive-craniectomy-related complications. Therapy-requiring intracranial hypertension and total ICP-treatment days are cohort-wide measures that may be evaluated in patients with or without decompressive craniectomy. Analyses will use multilevel models with center effects where feasible, propensity-score-based adjustment, weighting or matching, treatment-era adjustment, and timing-aware landmark, risk-set, or target-trial-emulation-oriented approaches when data granularity permits. These methods are intended to reduce confounding by indication, treatment-selection bias, center effects, calendar-time effects, timing bias, and immortal-time bias. Results will be interpreted as observational estimates and not as equivalent to randomized evidence. Only patient-level data without direct identifiers are transferred to the coordinating center. Where legally and institutionally authorized, pseudonymized patient-level data may be transferred while any re-identification key remains exclusively under local control; where pseudonymized transfer is not permitted, an anonymous site export is required. Each participating center must meet the applicable local ethics, data-protection, institutional, contractual, and international-transfer requirements before patient-level data transfer. Central transfer of DICOM or other source imaging is not part of the main study dataset. Imaging/DICOM/computer-vision/AI analyses and cranioplasty-related follow-up are optional future substudies requiring separate data specifications and any additional approvals applicable at that time.