Registry-Based Assessment of Shunt Operation Methods and Outcomes in Idiopathic Normal Pressure Hydrocephalus (RASHOMON Study): Protocol for a Multicenter Prospective Observational Cohort Study

Background Idiopathic normal pressure hydrocephalus is an age-related condition characterized by cerebrospinal fluid accumulation and ventricular enlargement, leading to cognitive decline, gait disturbance, and urinary incontinence. Although shunt surgery is the primary treatment, the optimal surgical strategy remains uncertain, and procedure selection is often not tailored to individual patient characteristics. Notably, no prospective study has directly compared the 3 major shunt techniques (ie, ventriculoperitoneal, lumboperitoneal, and ventriculoatrial). Objective This multicenter prospective observational study will aim to generate high-quality clinical evidence by evaluating the effectiveness and safety of the 3 aforementioned surgical options in a real-world setting. Methods Patients suspected of having this condition will be enrolled based on characteristic symptoms and imaging findings, with a spinal tap test recommended but not mandatory. Eligible patients will undergo one of the aforementioned surgical procedures. Results On the basis of recent data from 11 collaborating institutions in Japan, we estimate enrolling 278 cases: 188 (67.6%) surgical, 100 (36%) nonsurgical, and 10 (3.6%) dropouts. Clinical outcomes will be assessed at baseline; after the tap test (if performed); and at 1 week, 3 months, and 12 months postoperatively. The analyses will explore the associations between outcomes and surgical methods, patient backgrounds, and imaging features. As of May 2025, approximately 60 participants have been enrolled from 11 institutions. Data collection is ongoing and is expected to be completed by December 2026. There will be a 1-year follow-up period. The main study results are anticipated to be published in 2028. Conclusions Japan is well placed to lead this comparative study with its extensive experience in diagnosing and treating this disease. These findings are expected to provide practical guidance for individualized surgical decision-making and contribute to the global consensus on optimal treatment strategies. Trial Registration Japan Registry of Clinical Trials jRCT1040250005; https://jrct.mhlw.go.jp/latest-detail/jRCT1040250005 International Registered Report Identifier (IRRID) DERR1-10.2196/80678