OBJECTIVE: The main aim was to determine the incidence, risk factors, clinical phenotypes, and response to shunt surgery in chronic, shunt-dependent hydrocephalus (SDHC) after aneurysmal subarachnoid hemorrhage (aSAH). METHODS: In this observational, single-center study, 849 aSAH patients treated at Uppsala University Hospital between 2008-2018 were included. Variables on demography, injury severity, treatments, chronic hydrocephalus presentation, and outcome were evaluated. RESULTS: In total, 107 (13%) patients were treated with a shunt due to SDHC. In multivariate logistic regressions, risk factors for SDHC were worse neurologic (World Federation of Neurosurgical Societies) grade, larger ventricles (Evans index) at admission, the need to insert an external ventricular drain (EVD), decompressive craniectomy, and complications with meningitis. Six different SDHC phenotypes were identified: impeded neurological recovery (55%), Hakim-Adams syndrome (17%), high-pressure symptoms (13%), failed EVD removal (8%), external brain herniation after decompressive craniectomy (DC
6%), and subdural hygroma (1%). The former 3 groups significantly improved in modified Rankin Scale (mRS) and 87%-100% exhibited subjective symptomatic relief. There was no significant change in mRS for the latter 3 groups, but 60%-100% experienced some subjective relief postoperatively. CONCLUSIONS: Chronic SDHC was a common complication after aSAH, particularly in patients with severe primary brain injury, acute hydrocephalus, and treatment-related factors. The condition presents with distinct clinical phenotypes, which may influence treatment response. Recognizing these phenotypes could aid in optimizing patient selection and expectations for shunt surgery outcomes.