A Novel Approach to the Diagnosis of Idiopathic Intracranial Hypertension: Noninvasive Assessment Using the MRI-Based CSF Flow Rigidity Index and Conventional MRI-Derived Idiopathic Intracranial Hypertension-MR Score

BACKGROUND AND PURPOSE: Idiopathic intracranial hypertension (IIH) is a condition marked by elevated intracranial pressure, often leading to vision loss if untreated. While CSF opening pressure is a primary diagnostic criterion, it lacks sensitivity in normotensive cases. This study aimed to develop a noninvasive, imaging-based diagnostic model integrating a novel MRI-Rigidity Index (MRI-RI) and a conventional MRI-derived IIH–MR Score to assess intracranial rigidity and improve diagnostic accuracy across the IIH spectrum. MATERIALS AND METHODS: Sixty-one participants were prospectively analyzed and divided into 3 groups: confirmed IIH (n = 23), normotensive with IIH-compatible imaging (n = 18), and healthy controls (n = 20). The male-to-female distribution was 7/16 in group one, 5/13 in group two, and 8/12 in group three. All subjects underwent 1.5T MRI, including structural sequences and phase-contrast (PC) CSF flow imaging. The MRI-RI was calculated as Vmax^2 × |NFV| / Vmean, where Vmax reflects peak CSF flow velocity, Vmean represents mean flow velocity, and |NFV| denotes the net CSF displacement per cardiac cycle, calculated as a magnitude-based volumetric measure independent of flow direction. A 6-parameter IIH–MR Score (range: 0–10) quantified perioptic CSF distension, Meckel cave size, sella morphology, optic disc protrusion, optic nerve tortuosity, and posterior scleral flattening. Interobserver agreement, intergroup comparisons, receiver operating characteristic analysis, and correlation with CSF pressure were performed. RESULTS: MRI-RI and IIH–MR Scores differed significantly across groups (P < .001), with the highest values in confirmed IIH and the lowest in controls. A total MRI score ≥6 yielded 100% sensitivity and 92% specificity for detecting elevated CSF pressure; ≥7 provided 100% specificity. MRI-RI was notably elevated in normotensive patients with IIH-compatible features. Strong correlations were found between the total MRI score and CSF pressure (r = 0.85), and MRI-RI (r = 0.66). Interobserver agreement was excellent (intraclass correlation coefficient = 0.88–0.96; κ = 0.76–0.91). CONCLUSIONS: The combined use of the MRI-RI and IIH–MR Score allows comprehensive, noninvasive evaluation of intracranial rigidity in IIH. MRI-RI may detect early mechanical alterations even in normotensive patients, while the IIH–MR Score offers structurally grounded diagnostic support. These tools may enhance early diagnosis and reduce the need for lumbar puncture in selected cases.