Vestibular schwannoma associated normal pressure hydrocephalus: clinical features and shunt responsiveness compared with idiopathic NPH.
BACKGROUND: Vestibular schwannoma (VS) is commonly associated with obstructive hydrocephalus due to mass effect; however, a rarer communicating form resembling normal pressure hydrocephalus (NPH) has also been described, possibly related to impaired CSF absorption from elevated CSF protein. We aimed to characterize the clinical and imaging features of VS-associated NPH (VS-NPH) and compare them with those of an idiopathic NPH (iNPH) cohort. METHODS: We retrospectively analyzed 18 patients with VS-NPH identified between 2008 and 2024. For comparison, 41 iNPH patients were drawn from a prospective longitudinal study at our center. Variables included demographics, tumor size, VS treatment modality, CSF parameters, Radscale imaging features, and shunt responsiveness. RESULTS: VS-NPH patients had markedly higher CSF protein levels than patients with iNPH (median 100 vs. 51 mg/dL, p < 0.001). Radiological features largely overlapped; however, parasagittal sulcal narrowing was more frequent in VS-NPH (61 % vs.13 %, p = 0.002). These differences remained significant in the sensitivity analysis excluding the two patients without gait impairment. VS-NPH patients were younger in the primary analysis (66.8 vs. 72.0 years, p = 0.03), while exploratory associations between larger tumor size and both earlier NPH symptom onset (r = -0.48, p = 0.049) and smaller callosal angle (r = -0.49, p = 0.048) attenuated to non-significant trends in the sensitivity analysis. Tumor size was < 30 mm in 89 % of patients. Ventriculoperitoneal shunt (VPS) resulted in clinical improvement in both groups, although response rates were numerically lower in VS-NPH than in iNPH (63 % vs.75 %). CTT was positive in 9 of 11 VS-NPH patients who underwent testing, although improvement after shunting also occurred in patients with negative CTT results or without prior CTT. CONCLUSIONS: VS-NPH may represent a secondary subtype of NPH with distinct biochemical and subtle imaging features. Elevated CSF protein may contribute to altered CSF dynamics. These findings are exploratory and require confirmation in larger prospective studies.