31/07/2026
↕️🔁 Normal Pressure Hydrocephalus (NPH); Radiological Aspects☢️👁️🗨️
📌NPH is a potentially reversible cause of dementia, characterized by the classic clinical triad:
* Gait disturbance (earliest and most prominent)
* Cognitive impairment
* Urinary incontinence
🚨 Radiology plays a central role in diagnosis, patient selection for shunting, and excluding mimics.
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☢️1. CT and MRI Findings
🔻A. Ventriculomegaly (Essential Finding)
* Enlargement of the lateral and third ventricles
* Disproportionate to the degree of cerebral atrophy
* Fourth ventricle may be mildly enlarged
☑️B. Evans Index
The most widely used quantitative measurement.
📌Evans Index =
Maximum width of frontal horns ÷ Maximum internal skull diameter
* Normal: 0.33 are highly abnormal.
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📐C. Callosal Angle (MRI Coronal)
Measured on a coronal image perpendicular to the AC-PC line at the level of the posterior commissure.
* Normal: 100–120°
* NPH: 50–80°
* Helps distinguish NPH from ex-vacuo ventriculomegaly.
Smaller callosal angle strongly favors NPH.
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✅D. DESH Pattern
(Disproportionately Enlarged Subarachnoid Space Hydrocephalus)
One of the most characteristic MRI findings.
✳️Features include:
* Ventriculomegaly
* Dilated Sylvian fissures
* Tight high-convexity sulci
* Tight medial subarachnoid spaces
This pattern strongly supports NPH.
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↗️E. Temporal Horn Enlargement
Early enlargement of the temporal horns;
Usually:
* 2 mm
* Not explained by hippocampal atrophy
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⚠️F. Periventricular White Matter Signal
MRI:
* Periventricular T2/FLAIR hyperintensity
* Represents transependymal CSF flow and chronic ischemic change
May decrease after successful shunting.
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🌀G. Bowing of Corpus Callosum
Upward elevation and thinning due to enlarged ventricles.
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☢️↕️2. CSF Flow MRI (Phase-Contrast MRI)
Can demonstrate:
* Increased aqueductal CSF velocity
* Increased aqueductal stroke volume
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🚨📌Differential Diagnosis⁉️
❇️Radiologically distinguish NPH from:
* Alzheimer disease
* Vascular dementia
* Ex-vacuo ventriculomegaly
* Obstructive hydrocephalus
* Long-standing overt ventriculomegaly in adults (LOVA)
* Chronic communicating hydrocephalus after subarachnoid hemorrhage or meningitis
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🔻☢️High-yield radiology pearls
* DESH is one of the most specific imaging patterns for idiopathic NPH.
* Evans index ≥0.30 supports ventriculomegaly but is not diagnostic by itself.
* Callosal angle