What are the typical findings on an MRI of the brain in a patient with Pseudotumor Cerebri (Idiopathic Intracranial Hypertension - IIH)?

MRI Findings in Pseudotumor Cerebri (Idiopathic Intracranial Hypertension)

MRI of the brain in pseudotumor cerebri typically shows normal brain parenchyma without mass, hydrocephalus, or abnormal meningeal enhancement, but demonstrates specific secondary signs of elevated intracranial pressure including empty sella, posterior globe flattening, optic nerve changes, and enlarged optic nerve sheaths. 1

Key MRI Findings (Ranked by Specificity)

Highly Specific Findings (100% Specificity)

• Posterior globe flattening - Present in 80% of cases with 56% sensitivity and 100% specificity 1, 2
• Intraocular protrusion of the optic nerve - Seen in 30-40% of cases with 40% sensitivity and 100% specificity 1, 2

Moderately Specific Findings

• Horizontal/vertical tortuosity of the optic nerve - Present in 40-68% of cases with 68% sensitivity and 83% specificity 1, 2
• Empty sella or partially empty sella - Found in 70% of cases, a hallmark feature of chronically elevated intracranial pressure 1, 2
• Distension of the perioptic subarachnoid space - Detected in 45% of cases 1, 2

Additional Supportive Findings

• Enlarged optic nerve sheath - Mean diameter of 4.3 mm in IIH patients versus 3.2 mm in controls 1
• Smaller pituitary gland size - Mean 3.63 mm in IIH versus 5.05 mm in controls 1
• Enhancement of the prelaminar optic nerve - Present in 50% of cases (not seen in normal controls) 2

Optimal Imaging Protocol

The American College of Radiology recommends MRI of the head and orbits as the most useful imaging modality because it provides superior resolution of intracranial and intraorbital structures compared to CT. 1

Essential Sequences

• MRI brain with and without contrast to exclude secondary causes of elevated intracranial pressure 3
• Dedicated orbital imaging with coronal, fat-saturated T2-weighted sequences to evaluate optic nerve sheaths 4
• MR venography (MRV) to demonstrate narrowing of the distal transverse sinuses and exclude cerebral venous sinus thrombosis 1

What MRI Must Exclude

The diagnosis of pseudotumor cerebri requires demonstrating normal brain parenchyma on imaging with absence of: 1

• Mass lesions
• Hydrocephalus
• Abnormal meningeal enhancement

Clinical Correlation

When to Suspect the Diagnosis

Even in the absence of papilledema and sixth nerve palsy, pseudotumor cerebri can be suggested based on the constellation of MRI findings listed above. 1

Diagnostic Accuracy

Based on the MRI signs described, examiners can predict the presence of elevated intracranial pressure in 90% of pseudotumor cerebri cases and correctly identify normal pressure in 100% of control subjects. 2

Important Pitfalls

• Do not confuse cerebellar tonsillar ectopia >5mm with Chiari I malformation - this can be secondary to pseudotumor cerebri itself 4
• Meningeal enhancement after lumbar puncture is expected and should not be misinterpreted as pathology 4
• Each individual MRI finding has limited sensitivity (30-80%), but the combination of multiple findings significantly increases diagnostic confidence 2
• CT imaging is less sensitive for detecting these subtle findings and should not be the primary modality for evaluation 4