Suspected normal pressure hydrocephalus
ACR AC Dementia (2024 update); NPH imaging literatureThe imaging question is not simply whether the ventricles are large — it is whether they are large out of proportion to atrophy, which is a pattern judgement that MRI supports and a report of "ventriculomegaly" does not.
Older patient with the triad of a magnetic gait, cognitive slowing and urinary urgency, where a potentially treatable cause of decline is being sought.
Referenced decision support — confirm against your local protocol.
Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.
Accept as requested
MRI Brain — routine unenhanced
MRI Brain
What we'd amend, and why
- The diagnosis depends on comparing ventricular size against cortical sulcal volume in defined places, and on a mid-sagittal measurement of the callosal angle — neither of which is reliable on axial CT sections angled variably to the skull base. MRI additionally shows the aqueduct and the posterior fossa, distinguishing a communicating pattern from an obstructive one, and grades the coexisting small vessel disease and medial temporal atrophy that predict a poor response to shunting.
Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.
How was this decided?
- pathwayadult — Adults
- rulerule-mr-device-screening — MR safety screening for implants and foreign bodies; checked by Radiographer at the scanner
- rulerule-paeds-sedation — Sedation or anaesthesia for a child; checked by Nurse before the scan
Decision support only. Local protocol takes precedence.
Handled at the scanner(1)nothing for you to do
Settled and owned downstream. Each returns to a radiologist only on the stated trigger.
- MR safety screening for implants and foreign bodiesComplete the MR safety questionnaire, verify implant labelling and its stated conditions of use against this scanner and this protocol, and ensure no ferromagnetic object enters Zone IV.Radiographer at the scannerBefore the scanFlags back if: An implant or retained foreign body that is MR Unsafe, unlabelled, or cannot be identified; or an MR Conditional device whose stated conditions this scanner or the requested protocol cannot satisfy; or a credible unexcluded intraocular metallic foreign body history.
Pathways
Big forks are separate pathways; the first whose conditions match is the one used.
Adults
Matches your inputsDefault| Role | Study & protocol | Why this answers the question |
|---|---|---|
| First line | MRI Brain MRI Brain — routine unenhanced usually appropriate | The diagnosis depends on comparing ventricular size against cortical sulcal volume in defined places, and on a mid-sagittal measurement of the callosal angle — neither of which is reliable on axial CT sections angled variably to the skull base. MRI additionally shows the aqueduct and the posterior fossa, distinguishing a communicating pattern from an obstructive one, and grades the coexisting small vessel disease and medial temporal atrophy that predict a poor response to shunting. |
| Reasonable alternative | CT Head CT Head — Unenhanced | Acceptable where MRI cannot be tolerated or obtained, and it is the routine study for a suspected shunt malfunction in a patient who already has one. It can measure the Evans index and show gross disproportion, but it assesses the callosal angle and the convexity sulci poorly and misses the mimics that MRI would catch. |
Pitfalls
- Reporting ventriculomegaly without commenting on the proportion to atrophy, which is the only part of the finding that discriminates.
- Relying on the Evans index alone. Its specificity is limited and it is measured differently by different observers.
- Missing an obstructive cause at the aqueduct or in the posterior fossa, which turns a shunt discussion into a different operation.
- Overlooking bilateral chronic subdural collections, which mimic the clinical triad and are treated by drainage rather than shunting.
- Treating severe medial temporal atrophy and heavy small vessel disease as incidental — both predict a poor response to shunting and belong in the report.
Priors — what to pull first
- Serial imaging is far more informative than a single study: progressive ventricular enlargement without progressive sulcal widening is the strongest radiological argument.
- In a shunted patient, the baseline post-shunt scan is the comparator, not the pre-operative one.
What makes a good request
- Ventriculomegaly is common in the elderly and most of it is atrophic. The distinguishing pattern is disproportionate enlargement of the ventricles with tight high convexity sulci and widened Sylvian fissures, together with a narrowed callosal angle.
- Measurements are supportive rather than diagnostic. An Evans index above 0.3 is the conventional entry criterion, but it has poor specificity on its own and the diagnosis remains clinical plus radiological plus response to cerebrospinal fluid drainage.
- The scan must also exclude the obstructive causes — aqueduct stenosis, a posterior fossa lesion, chronic subdural collections — which are managed completely differently.
Scoring this once it is done
The classification and risk tools this question ends in.
How these studies are acquired
Contrast, phases and timing for every study on the pathways above.
Confirm locally
- MRI Brain — routine unenhanced: timings are typical — confirm against local protocol.
- Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
- Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.
References
- Neuroimaging in normal pressure hydrocephalus · Primary literature
- Diagnosis of normal-pressure hydrocephalus: use of traditional measures in the era of volumetric MR imaging (Radiology 2017) · Primary literature
- ACR Appropriateness Criteria — Dementia (2024 update) · ACR Appropriateness Criteria
- American College of Radiology Manual on MR Safety: 2024 Update and Revisions. Radiology. · ACR MR Safety
- ACR Manual on MR Safety — zoning, MR Safe / MR Conditional / MR Unsafe labelling, and screening of patients and personnel · ACR MR Safety
- Safety of MRI in patients with cardiac implantable electronic devices — conditions of use, device interrogation and monitoring · Primary literature
- AAP/AAPD Guidelines for Monitoring and Management of Pediatric Patients Before, During, and After Sedation for Diagnostic and Therapeutic Procedures. Pediatrics 2019;143(6):e20191000. · Other
- Sedation and anaesthesia for imaging of the infant and neonate — a brief review (feed-and-wrap, fasting, monitoring) · Primary literature
- Image Gently — reducing the need for sedation through preparation and faster protocols in paediatric imaging · Image Gently
Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.