Neurologic Imaging

What Imaging Is Best for Suspected Normal Pressure Hydrocephalus in Adults?

·
What Imaging Is Best for Suspected Normal Pressure Hydrocephalus in Adults?

An 81-year-old male is brought to your clinic by his family due to a one-year history of progressive memory problems, a shuffling, magnetic gait, and new-onset urinary incontinence. The classic triad immediately brings idiopathic normal pressure hydrocephalus (NPH) to the top of your differential. You know that NPH is one of the few reversible causes of dementia, but the diagnosis hinges on correlating the clinical picture with specific imaging findings. The question is which initial study to order to confirm ventriculomegaly and rule out mimics. This article provides a step-by-step workflow for this exact scenario, guided by the American College of Radiology (ACR) Appropriateness Criteria, which rate an MRI head without IV contrast as Usually Appropriate.

Who Fits This Clinical Scenario?

This guidance is for an adult patient presenting with cognitive impairment accompanied by at least one of the other two classic NPH symptoms: gait disturbance or urinary incontinence. The onset is typically insidious and progressive. The key is the combination of cognitive decline with these specific motor or autonomic symptoms, which points away from more common dementia etiologies and toward a potential cerebrospinal fluid (CSF) dynamics problem.

This workflow is NOT intended for patients with:

  • Isolated cognitive impairment or memory loss: A patient with memory deficits but a normal gait and no incontinence may better fit the workup for suspected Alzheimer disease. This is a distinct clinical scenario with its own imaging pathway.
  • Cognitive impairment dominated by behavioral changes or aphasia: Prominent personality changes, disinhibition, or progressive language difficulty suggests a workup for frontotemporal dementia, another separate ACR variant.
  • Acute neurologic changes: A sudden change in mental status, severe headache, or focal neurologic deficits requires an emergent evaluation for stroke, hemorrhage, or acute hydrocephalus, not the subacute workup described here.

Correctly identifying your patient’s presentation is crucial for selecting the most diagnostic and cost-effective initial imaging study.

What Diagnoses Are You Working Up in This Scenario?

When you order imaging for a patient with suspected NPH, you are primarily investigating for structural changes in the brain while simultaneously ruling out other conditions that can mimic the presentation. The differential diagnosis is focused and consequential.

Normal Pressure Hydrocephalus (NPH) is the leading consideration. This condition is characterized by ventriculomegaly (enlarged brain ventricles) without a corresponding increase in CSF pressure on lumbar puncture. The prevailing theory is that impaired CSF absorption leads to its accumulation, stretching the periventricular white matter tracts that control gait, cognition, and bladder function. Imaging is essential to identify the characteristic ventriculomegaly that is out of proportion to the degree of sulcal widening.

Cerebral Atrophy (Hydrocephalus ex Vacuo) is a critical alternative to differentiate. In neurodegenerative conditions like Alzheimer disease, brain tissue volume is lost, and the ventricles and sulci passively enlarge to fill the space. This is termed hydrocephalus ex vacuo. Unlike NPH, the ventriculomegaly is proportional to the sulcal widening. Distinguishing this from NPH is a primary goal of imaging, as the treatments are entirely different.

Chronic Subdural Hematoma or Hygroma can present insidiously in older adults, often after minor or even forgotten head trauma. A slow accumulation of blood or fluid over the brain surface can cause mass effect, leading to cognitive slowing, gait imbalance, and headaches. Imaging readily identifies these extra-axial fluid collections.

Vascular Dementia resulting from extensive small vessel ischemic disease can also manifest with both cognitive and gait impairments (a “vascular parkinsonism”). Imaging can reveal widespread white matter changes, lacunar infarcts, or evidence of prior strokes that would support this diagnosis over NPH.

Why Is MRI Head Without IV Contrast the Recommended Study for This Presentation?

The ACR designates MRI head without IV contrast as Usually Appropriate for the initial evaluation of suspected NPH. This recommendation is based on its superior ability to visualize key anatomical features and rule out mimics without exposing the patient to ionizing radiation.

The rationale for this choice includes:

  • Superior Soft Tissue Contrast: MRI provides exquisite detail of the brain parenchyma, CSF spaces, and sulcal patterns. This allows for a confident assessment of ventriculomegaly and, crucially, its proportionality to sulcal effacement. Radiologists look for specific signs suggestive of NPH, such as disproportionately enlarged subarachnoid-space hydrocephalus (DESH), which includes enlarged Sylvian fissures with compressed sulci at the vertex. MRI is also highly sensitive for the subtle periventricular signal changes (transependymal edema) that can indicate abnormal CSF pressure.
  • Exclusion of Mimics: A non-contrast MRI is excellent for identifying alternative diagnoses. It can clearly depict chronic subdural hematomas, evidence of extensive small vessel ischemic disease, and most brain tumors that could cause obstructive hydrocephalus.
  • No Ionizing Radiation: MRI uses magnetic fields and radio waves, avoiding the radiation exposure associated with CT scans. This is a key advantage, particularly if follow-up imaging may be needed. The relative radiation level (RRL) is O (0 mSv).

Why are alternative studies rated lower for this initial workup?

  • CT head without IV contrast is also rated Usually Appropriate and is a valid alternative, especially if MRI is unavailable, contraindicated (e.g., incompatible pacemaker), or the patient is claustrophobic. It can readily show ventriculomegaly. However, its soft tissue resolution is lower than MRI, making it harder to assess for DESH or subtle periventricular edema. It also involves radiation exposure (RRL ☢☢☢, 1-10 mSv).
  • MRI head without and with IV contrast is rated Usually not appropriate. For the initial workup of idiopathic NPH, gadolinium contrast adds little diagnostic information. It does not help differentiate NPH from atrophy and introduces unnecessary cost and the small risk of adverse reactions. Contrast should be reserved for cases where the non-contrast study reveals a finding suspicious for a tumor, infection, or inflammatory process.

What’s Next After MRI Head Without IV Contrast? Downstream Workflow

The imaging report is not the end of the diagnostic journey; it’s a critical input into the subsequent clinical workflow. Your next steps will be dictated by the MRI findings.

  • If the MRI is highly suggestive of NPH: Findings like marked ventriculomegaly out of proportion to sulcal widening and a tight vertex (DESH sign) strongly support the diagnosis. The definitive next step is typically a diagnostic and therapeutic large-volume lumbar puncture (LP). Approximately 30-50 mL of CSF is removed, and the patient’s gait and cognitive function are formally assessed before and after the procedure. A significant, albeit often temporary, improvement in symptoms after the LP is a strong positive predictor of response to a ventriculoperitoneal (VP) shunt.
  • If the MRI shows global cerebral atrophy: When ventriculomegaly is proportional to widespread sulcal widening, the diagnosis is more likely a primary neurodegenerative dementia like Alzheimer disease. The workup should then pivot toward that diagnosis, which may involve neuropsychological testing and, in some cases, more advanced imaging like amyloid or tau PET scans. A large-volume LP is not indicated.
  • If the MRI reveals an alternative cause: Should the scan identify a chronic subdural hematoma, extensive vascular disease, or a mass lesion, the workflow shifts entirely. The patient should be referred to the appropriate specialist (e.g., neurosurgery for a hematoma, neurology/stroke clinic for vascular dementia) for management of that specific condition.
  • If the MRI is equivocal: In borderline cases, where ventricles are moderately enlarged but other signs are ambiguous, further testing may be considered. This could include extended lumbar drainage (removing CSF over several days) or, less commonly, a radionuclide cisternogram (DTPA cisternography, rated May be appropriate by the ACR) to evaluate CSF flow dynamics.

Pitfalls to Avoid (and When to Get Help)

Navigating the workup for suspected NPH requires careful integration of clinical and imaging findings. Be mindful of these common pitfalls:

  • Mistaking Atrophy for NPH: Do not anchor on ventriculomegaly alone. This finding is common in the elderly. The key is the disproportion between ventricular size and sulcal size. Look for the DESH sign in the radiology report.
  • Ignoring the Clinical Triad: Imaging findings consistent with NPH are not diagnostic in a vacuum. The patient must have the corresponding clinical symptoms. An asymptomatic patient with large ventricles does not have NPH.
  • Overlooking Secondary Causes: Always scrutinize the imaging for evidence of a prior event (hemorrhage, meningitis, trauma) that could have caused a secondary, or non-idiopathic, NPH.
  • Delaying Action on Red Flags: If a patient presents with acute symptoms, papilledema, or severe headache, this is not a typical NPH workup. This suggests high-pressure, obstructive hydrocephalus, a neurologic emergency requiring immediate imaging and neurosurgical consultation.

Related ACR Topics and Tools

For a comprehensive overview of imaging for all dementia-related scenarios, from mild cognitive impairment to Alzheimer disease, please consult our parent guide. The tools below can help you navigate adjacent criteria, understand imaging techniques, and discuss radiation safety with your patients.

Frequently Asked Questions

Why is MRI preferred over CT if both are rated ‘Usually Appropriate’ for suspected NPH?

While both can identify ventriculomegaly, MRI is generally preferred due to its superior soft tissue contrast, which allows for a more detailed assessment of the specific features of NPH, such as disproportionately enlarged subarachnoid-space hydrocephalus (DESH). MRI is also better at detecting subtle alternative diagnoses like small infarcts or periventricular white matter changes and does so without any ionizing radiation.

Is a contrast-enhanced MRI ever needed in the workup for NPH?

For the initial evaluation of suspected idiopathic NPH, intravenous contrast is rated ‘Usually not appropriate’ as it does not add diagnostic value. However, if the non-contrast MRI reveals an unexpected finding, such as a mass or signs of inflammation, a follow-up study with contrast may be ordered to better characterize that specific abnormality.

What specific MRI findings strongly suggest NPH over simple brain atrophy?

The most specific finding is ventriculomegaly that is out of proportion to the degree of sulcal widening, particularly at the high convexity of the brain. This pattern is often called DESH (disproportionately enlarged subarachnoid-space hydrocephalus). It includes enlarged Sylvian fissures and temporal horns with tight, compressed sulci over the top of the head. An increased callosal angle on coronal images is another supportive finding.

If the MRI is suggestive of NPH, is that enough to make the diagnosis?

No. NPH is a clinical-radiological diagnosis. The imaging findings must be correlated with the clinical triad of gait disturbance, cognitive impairment, and urinary incontinence. Furthermore, a definitive diagnosis and prediction of treatment response typically requires a positive response to a large-volume lumbar puncture or extended lumbar drainage.

Can a patient have NPH if their brain ventricles are normal size on MRI?

It is highly unlikely. Ventriculomegaly is a required criterion for the diagnosis of NPH. A normal-sized ventricular system effectively rules out the condition and should prompt a search for other causes of the patient’s symptoms.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 29, 2026