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Imaging in Normal Pressure Hydrocephalus

Practice Essentials

First described by Hakim and Adams in 1965, normal pressure hydrocephalus (NPH) refers to a clinical entity consisting of the triad of gait disturbance, dementia, and incontinence, coupled with the laboratory findings of normal cerebrospinal fluid (CSF) pressures and radiographic findings of ventriculomegaly.
Although NPH is a relatively rare cause of dementia, identifying NPH is important because it is one of the few treatable entities. NPH serves as one of the reasons that all dementia patients should be evaluated with neuroimaging of either CT scanning or MRI as part of their workup.

It has been postulated that normal pressure hydrocephalus appears to be a “two-hit” disease: benign external hydrocephalus in infancy, followed by deep white matter ischemia in late adulthood.

An enlarged ventricular system out of proportion to sulcal atrophy (ventriculosulcal disproportion) is the most important imaging characteristic. Other radiologic markers such as narrowed temporal horns have been reported as statistically significant for the diagnosis of NPH.

An ongoing issue in the management of NPH is that clinical features and even some imaging features in patients with NPH can overlap with patients who have much more common diseases, such as Alzheimer disease with ex vacuo dilatation of the ventricles. Furthermore, the treatment of NPH is quite invasive, requiring intracranial procedures such as ventriculoperitoneal shunting. Thus, much imaging research has been devoted to trying to identify factors that can predict response to shunting.

MRI of the brain is the preferred radiologic examination for the diagnosis of NPH. T2-weighted images are especially helpful. CT scanning of the brain is useful if MRI is unavailable. Both radiologic techniques require clinical correlation. The primary role of MR and CT scanning is to assess for hydrocephalus with ventriculosulcal disproportion. This observation is a subjective assessment, and in patients with some sulcal widening or only minimal ventriculomegaly, the studies may not be sensitive or specific.  Further, MRI provides pathophysiologic information on CSF flow in patients with NPH.
 A correlation between clinical symptoms and stiffness values has also been suggested by MRI elastography.
 One of the most recent advancements with MRI is the assessment of some of the brain metabolic functions in patients with NPH via their glymphatic system.

Radiographic evaluation in the form of pneumoencephalographs has been completely replaced by CT and MRI and are now only of historical interest. Pneumoencephalography was used to demonstrate nonobstructive hydrocephalus. Intrathecally introduced air (via lumbar puncture) was found on radiographs within the enlarged lateral ventricles, not in the subarachnoid convexities. Ultrasonography is not used for the diagnosis of NPH, although some have suggested that reduced cerebral blood flow in NPH can be assessed by using transcranial Doppler ultrasound. 

The images below are examples of hydrocephalus ex vacuo and normal pressure hydrocephalus (NPH) from magnetic resonance imaging (MRI).

Axial T2-weighted magnetic resonance image of the

Axial T2-weighted magnetic resonance image of the brain in a patient with hydrocephalus ex vacuo. Note the enlarged ventricular system and noticeable sulcal atrophy.

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Axial T2-weighted magnetic resonance image of the

Axial T2-weighted magnetic resonance image of the brain in a patient with normal pressure hydrocephalus. Note the enlarged ventricular system, especially the atria of the lateral ventricles (V), which is out of proportion with sulcal atrophy.

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For excellent patient education resources, visit eMedicineHealth’s Brain and Nervous System Center. Also, see eMedicineHealth’s patient education article Normal Pressure Hydrocephalus.

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