Reduced cerebral blood flow of lingual gyrus associated with both cognitive impairment and gait disturbance in patients with idiopathic normal pressure hydrocephalus

•iNPH patients showed significantly poorer cognitive function than PD patients.•Motor dysfunction of the legs was similar between iNPH and PD patients.•Cognitive impairments were significantly correlated with motor dysfunctions in iNPH.•Decreased CBF of the lingual gyrus was associated with severe symptoms in iNPH.•Impaired brain connectivity of the occipital lobe may be related to severity of iNPH.