Idiopathic Normal Pressure Hydrocephalus: A Comprehensive Review

Idiopathic normal pressure hydrocephalus (iNPH) is a potentially reversible neurological disorder characterized by the triad of gait disturbance, cognitive decline, and urinary dysfunction in association with ventriculomegaly and normal or mildly elevated cerebrospinal fluid (CSF) pressure. Although first described by Hakim in 1957, the condition remains underdiagnosed, partly because its clinical manifestations are common in the elderly population and are often attributed to more prevalent age-related conditions. The pathophysiology of iNPH is complex and incompletely understood, involving alterations in CSF dynamics, reduced vascular compliance, periventricular ischemia, and dysfunction of the glymphatic system, potentially leading to the accumulation of neurotoxic metabolites and neuronal impairment. Neuroradiological studies, particularly MRI, play a central role in diagnosis. MRI is essential to exclude alternative causes of ventriculomegaly and to identify characteristic imaging features such as a reduced callosal angle and the disproportionately enlarged subarachnoid space hydrocephalus (DESH) pattern, which support the diagnosis, although their predictive value for treatment response remains limited. Complementary non-imaging tests are often required to identify patients most likely to benefit from CSF shunting. Recent MRI advances have introduced biomarkers of glymphatic dysfunction, such as diffusion tensor imaging along perivascular spaces (DTI-ALPS), which may improve understanding of disease mechanisms and refine patient selection. Early recognition and accurate imaging assessment are crucial, given the potential reversibility of symptoms after shunt surgery.