MRI Protocol for Pseudotumor Cerebri (Idiopathic Intracranial Hypertension)
MRI of the brain with and without contrast is the recommended imaging modality for pseudotumor cerebri, with additional MR venography to evaluate cerebral venous sinuses. 1
Primary Imaging Protocol
- MRI brain with and without contrast is the most appropriate imaging study for suspected pseudotumor cerebri because it is more sensitive for detecting secondary signs of increased intracranial pressure 1
- MR venography (MRV) should be included to evaluate for venous outflow obstruction or stenosis, which is commonly associated with pseudotumor cerebri 1
- Imaging of the orbits including a coronal, fat-saturated T2-weighted sequence should be included to better evaluate for dilatation of the optic sheaths 1
Key Diagnostic Findings on MRI
- Empty or partially empty sella (70% sensitivity) 2, 3
- Flattening of the posterior aspects of the globes (80% sensitivity, 100% specificity) 2, 3
- Dilated optic nerve sheaths 1, 2
- Tortuous or enhancing optic nerves 1, 3
- Vertical tortuosity of the orbital optic nerve (40% sensitivity) 3
- Intraocular protrusion of the prelaminar optic nerve (30% sensitivity, 100% specificity) 2, 3
MR Venography Considerations
- MRV can be performed with or without IV contrast, though contrast-enhanced MRV may be helpful when evaluating areas such as the sigmoid venous sinuses that are often degraded by artifact on non-contrast MRV 1
- MRV is particularly important to evaluate for venous sinus stenosis, which is present in many patients with pseudotumor cerebri 4
- In patients with suspected pseudotumor cerebri, repeat MRV after CSF drainage may be helpful to determine if venous outflow obstruction is primary or secondary to increased intracranial pressure 1
Alternative Imaging Options
- CT venography (CTV) can be considered as an alternative to MRV if MRI is contraindicated, though MRV is generally preferred due to radiation concerns 1
- Standard CT imaging is not recommended as the primary modality for pseudotumor cerebri evaluation as it is less sensitive for detecting the subtle findings associated with increased intracranial pressure 1
Clinical Correlation
- MRI findings should be correlated with clinical presentation, including headache, visual disturbances, and papilledema 5
- Normal brain parenchyma without evidence of hydrocephalus, mass, or structural lesion is expected in pseudotumor cerebri 1
- It's important to note that meningeal enhancement can be seen on MRI after lumbar puncture and should not be confused with pathology 1
Pitfalls and Caveats
- MRI may appear completely normal in some cases of pseudotumor cerebri, so the absence of radiological signs does not exclude the diagnosis 6
- Cerebellar tonsillar ectopia >5mm may be misdiagnosed as Chiari I malformation when it's actually related to pseudotumor cerebri 1
- In atypical cases (e.g., male, thin, or elderly patients), more extensive imaging workup may be needed to rule out secondary causes 7