General description

Normal pressure hydrocephalus (NPH) is a syndrome characterized by the classic triad of gait disturbance (typically a magnetic gait), urinary incontinence, and cognitive impairment. Despite its name, NPH refers to communicating hydrocephalus without elevated cerebrospinal fluid (CSF) pressure, which can result from impaired CSF resorption at the arachnoid granulations. NPH is classified into two types: secondary NPH, which occurs as a complication of other conditions such as subarachnoid hemorrhage, meningitis, or traumatic brain injury, and idiopathic NPH (iNPH), where no underlying cause is identified.

The gait disturbance is often the earliest and most characteristic feature, manifesting as unsteadiness and impaired balance. Cognitive impairment, particularly affecting executive function and attention, often appears later, with memory impairment occurring in more advanced stages. Urinary incontinence is common and may progress over time.

Diagnosis of iNPH typically involves clinical criteria and imaging findings. Patients over 60 years old presenting with one or more of the triad symptoms, ventricular enlargement on imaging, and normal CSF pressure are categorized as possible iNPH. If these patients respond to CSF removal (e.g., lumbar puncture), they are classified as probable iNPH, and those showing improvement after shunt surgery are deemed definite iNPH.

NPH accounts for up to 6% of dementia cases and should not be confused with other forms of dementia, which are often irreversible, or with delirium, which is typically acute and reversible.

Radiographic features

Ventricular enlargement in iNPH is evaluated using the Evans index, which is defined as the maximum width of the anterior horn of the lateral ventricles divided by the width of the cranium. An Evans index greater than 0.3 suggests iNPH.

Imaging studies also reveal widening of the Sylvian fissures and narrowing of the cerebral sulci at the high convexity. Tightening of the high convexity includes narrowing of the posterior cingulate sulcus and the marginal sulcus.