Risk Factors for Sinking Skin Flap Syndrome After Decompressive Craniectomy in Aneurysmal Subarachnoid Hemorrhage

Background To evaluate clinical, radiological, and procedural risk factors for sinking skin flap syndrome (SSFS) following decompressive craniectomy (DC) in a homogenous cohort of aneurysmal subarachnoid hemorrhage (aSAH) patients. Methods Patients who underwent DC for aSAH between 2014–2024 were retrospectively reviewed. Demographic variables, hemorrhage severity scores, CSF diversion characteristics, craniectomy morphometry, and radiological measurements were compared between patients with and without SSFS. Time-to-event analysis was used to characterize SSFS onset. Mann–Whitney U and Fisher’s exact tests were applied for group comparisons. A multivariable logistic regression model was constructed including craniectomy area and CSF diversion duration. Results Fifteen patients met inclusion criteria; four (27%) developed SSFS. Baseline demographics, hemorrhage grades, and aneurysm features were comparable between groups. SSFS patients had significantly larger craniectomy areas and exhibited greater flap sinking and paradoxical midline shift. CSF diversion duration was longer in SSFS patients but not statistically significant. SSFS occurred at a median of 265 days after DC, and all affected patients showed neurological improvement following cranioplasty. Non-SSFS patients had adequate at-risk follow-up without events. Conclusion In aSAH patients, larger craniectomy area is a strong predictor of SSFS, while prolonged CSF diversion demonstrates a non-significant trend toward increased risk. Diagnostic delays in the complex aSAH postoperative course may mask true onset. Radiological sinking alone is insufficient for diagnosis, as asymptomatic flap depression also occurred. Improved awareness is required to avoid both under- and overdiagnosis, and larger multicenter studies are needed to define clinical and radiological thresholds for SSFS.