What is the role of a cisternogram (cerebrospinal fluid flow study) in diagnosing and managing Normal Pressure Hydrocephalus (NPH)?

Role of Cisternogram in Normal Pressure Hydrocephalus

Cisternography (DTPA radionuclide cisternography) should NOT be used as the sole basis for deciding whether to proceed with shunt surgery in NPH, despite its ability to demonstrate characteristic CSF flow abnormalities. 1

Primary Imaging Recommendation

MRI head without IV contrast is the preferred initial imaging modality for suspected NPH, not cisternography. 2 MRI can identify all classic NPH findings including:

• Ventriculomegaly (Evans index >0.3) 2
• Narrowed posterior callosal angle (<90°) 2
• Effaced sulci along high convexities with widened Sylvian fissures (DESH pattern) 2
• Periventricular white matter changes 2
• Cerebral aqueduct flow void (cannot be seen on CT and correlates with shunt responsiveness) 2

CT head without IV contrast is an acceptable alternative when MRI is contraindicated, though it has lower sensitivity for periventricular changes and cannot detect aqueduct flow voids. 2

What Cisternography Shows (But Why It's Insufficient)

DTPA cisternography demonstrates characteristic NPH patterns: 1

• Persistent radiotracer activity in lateral ventricles at 24 hours
• Absence of radiotracer activity over cerebral convexities on delayed imaging
• Early ventricular reflux 3

The critical limitation: According to the American College of Radiology 2025 guidelines, evidence is insufficient to proceed with shunting based upon DTPA cisternography findings alone, even though some studies show correlation with positive shunt response. 1

Evidence Quality Issues

While older research suggested cisternography had reasonable sensitivity (87.5%) and specificity (77.8%) for predicting shunt response 3, and some studies considered it the "most physiological method" for CSF dynamics 4, current clinical practice guidelines explicitly state this evidence is insufficient for treatment decisions. 1

One prospective study of 70 iNPH patients found that cisternography did not provide additional diagnostic value for predicting shunt response among properly selected patients, with poor specificity (20% for ventricular stasis, 0% for surface stasis). 5

When Cisternography Might Be Considered

The 2020 ACR guidelines note that SPECT/CT cisternography may provide better anatomic localization than planar imaging 1, but this remains a second-tier test that cannot independently justify surgical intervention.

Brain perfusion SPECT with acetazolamide challenge (measuring cerebral blood flow reactivity) may help identify patients more likely to respond to shunting 1, but this is distinct from standard cisternography.

Clinical Decision Algorithm

1. Start with MRI head without contrast (or CT if MRI contraindicated) 2
2. Confirm clinical triad: gait disturbance (earliest), urinary incontinence, cognitive impairment 2
3. Document normal CSF opening pressure on lumbar puncture 6
4. If diagnosis remains uncertain after structural imaging, consider semi-invasive testing such as:
   • High-volume CSF tap with clinical response assessment 6, 3
   • Continuous CSF pressure monitoring
   • External lumbar drainage trial
5. Cisternography findings alone should never be the deciding factor for shunt surgery 1

Critical Pitfall

Do not deny shunt surgery to an otherwise appropriate NPH candidate based solely on negative or equivocal cisternography results. The test lacks sufficient evidence to exclude patients from potentially beneficial treatment. 1