Specific CT Brain Scan Findings in Normal Pressure Hydrocephalus
CT head without IV contrast demonstrates ventriculomegaly as the primary finding in NPH, though it has lower sensitivity than MRI for detecting other characteristic features and should be reserved for cases where MRI is contraindicated or unavailable. 1, 2
Primary CT Finding
- Ventriculomegaly is the cardinal radiological feature visible on CT scan, representing enlargement of the lateral ventricles disproportionate to cortical atrophy 2, 3
Additional CT Features (Less Reliably Detected)
While CT can identify ventriculomegaly, it has significant limitations compared to MRI for detecting the following NPH-specific features:
- Periventricular white matter changes may be visible but are less well-characterized on CT compared to MRI 2, 3
- Sulcal effacement along the high convexities with relatively preserved sylvian fissures (the DESH pattern - Disproportionately Enlarged Subarachnoid space Hydrocephalus) is poorly visualized on CT 2
- Narrowed posterior callosal angle is difficult to assess accurately on CT 2, 3
Critical Imaging Recommendation
MRI brain without IV contrast is the preferred and recommended initial imaging modality for NPH diagnosis due to its superior ability to detect characteristic features that CT may miss. 1, 2, 3
Key MRI advantages include:
- Better visualization of the narrowed posterior callosal angle 2, 3
- Detection of cerebral aqueduct flow void indicating hyperdynamic CSF flow 2, 3
- Clear demonstration of the DESH pattern (effaced sulci at high convexities with widened sylvian fissures) 2
- Superior characterization of periventricular white matter changes 2, 3
Clinical Context for Imaging Interpretation
When interpreting imaging findings, correlate with the clinical triad that develops sequentially:
- Gait disturbance occurs first in approximately 70% of patients, characterized by a magnetic or "feet glued to floor" appearance 1, 4
- Cognitive impairment develops later with frontal-subcortical pattern (psychomotor slowing, attention deficits, working memory impairment, executive dysfunction) 1, 3
- Urinary incontinence or urgency completes the triad 2
Common Pitfalls to Avoid
- Do not rely solely on CT findings when MRI is available - CT's lower sensitivity may lead to missed diagnoses or failure to identify optimal surgical candidates 2
- Recognize that 20-57% of NPH patients have comorbid Alzheimer's disease or other neurodegenerative conditions, making imaging correlation with clinical findings essential 1, 3
- Ventriculomegaly alone is insufficient for diagnosis - it must be correlated with the appropriate clinical syndrome and ideally confirmed with additional MRI features 2, 3
Treatment Implications
- NPH represents one of the few potentially reversible causes of dementia, affecting approximately 3.7% of patients over 65 years 1
- Properly selected patients have an 80-90% chance of responding to ventriculoperitoneal shunt surgery 1
- Positive imaging findings should prompt referral to neurosurgery for shunt evaluation 2