Regional signature of normal pressure hydrocephalus on FDG PET

1081 Introduction: Whereas on MRI, ventricular dilation and tight high convexity support the diagnosis of idiopathic normal pressure hydrocephalus (iNPH), for FDG PET no regional signature of iNPH has been established yet. We explored whether regional cerebral glucose metabolism differs between patients with and without NPH-suggestive findings on MRI. We evaluated data of patients who had received FDG PET and MRI for diagnosis of neurodegenerative disease. MRI of 346 patients were visually read (supported by voxel-based morphometry) and assigned to either of the two groups of patients with (N = 88) or without MRI signs of iNPH (N = 258). FDG PET scans were preprocessed and compared between groups using SPM12 (adjusted for age; p 100 voxels). In a subgroup analysis, only patients with clinical iNPH and a typical MRI pattern were compared to those without MRI features of iNPH. Patients with features of iNPH on MRI showed a higher FDG uptake at the high convexity, including the central region. This was replicated in patients with clinical iNPH and a typical MRI pattern. Decreased FDG uptake in patients with MRI signs of iNPH was only observed in the vicinity of the ventricles (most likely partial volume effects). The tight high convexity on MRI is reflected by increased FDG uptake of the same region, especially when compared to patients with possible neurodegenerative disease, a frequent differential diagnosis of iNPH. The diagnostic value of this signature remains to be validated in a further prospective study.