What is the best diagnostic imaging study to evaluate for an aneurism and other causes of positional vertigo in the brain?

MRA Brain for Aneurysm and Positional Vertigo Evaluation

For evaluating aneurysms, MRA head without or with IV contrast is highly appropriate (rated 8/9), with similar sensitivity (95%) but lower specificity (89%) compared to CTA, making either contrast protocol acceptable based on patient factors. 1 However, for positional vertigo evaluation, MRI/MRA is generally unnecessary unless red flags for central pathology are present. 1, 2

Aneurysm Detection: MRA Protocol Selection

Both MRA protocols perform equivalently for aneurysm detection:

• MRA head without IV contrast achieves 95% sensitivity and 89% specificity for aneurysm detection, with improved accuracy for aneurysms >5mm and at 3T field strength 1
• MRA head without and with IV contrast provides identical diagnostic performance (95% sensitivity, 89% specificity) 1
• The addition of contrast may improve visualization of large aneurysms with complex flow dynamics or thrombosis, but does not significantly change overall diagnostic accuracy 1

Choose MRA without contrast when:

• Patient has renal failure or contrast allergy 1
• Standard aneurysm screening is needed 1
• Cost containment is a priority (single sequence vs. dual sequence)

Choose MRA with contrast when:

• Evaluating complex or previously treated aneurysms 1
• Assessing for enhancing pathology beyond vascular structures 1

Positional Vertigo: When MRI/MRA Is NOT Indicated

MRI/MRA is unnecessary for typical positional vertigo (BPPV) with characteristic findings on Dix-Hallpike maneuver. 1, 2, 3

Imaging is NOT appropriate when:

• Dix-Hallpike maneuver produces torsional and upbeating nystagmus with 5-20 second latency, crescendo-decrescendo pattern, and resolution within 60 seconds 2, 3
• No neurological deficits are present 1, 2
• Symptoms respond to canalith repositioning procedures (Epley maneuver) 2, 3
• The diagnostic yield of imaging in isolated dizziness is only 4%, making routine imaging wasteful 3

Red Flags Demanding Urgent MRI for Vertigo

Obtain MRI head without IV contrast immediately if ANY of the following are present: 1, 2, 3

• Severe postural instability with falling (suggests vertebrobasilar insufficiency or cerebellar pathology) 1, 2
• New-onset severe headache with vertigo (may indicate vertebrobasilar stroke or hemorrhage) 2, 3
• Any additional neurological symptoms: dysarthria, dysmetria, dysphagia, sensory/motor deficits, diplopia, Horner's syndrome 2
• Atypical nystagmus patterns:
  • Purely vertical nystagmus without torsional component 2, 3
  • Downbeating nystagmus on Dix-Hallpike without torsional component 2, 3
  • Direction-changing nystagmus without head position changes 2
  • Baseline nystagmus present without provocative maneuvers 2
  • Nystagmus not suppressed by visual fixation 1, 2
• Failure to respond to appropriate peripheral vertigo treatments 2, 3
• High vascular risk factors (hypertension, atrial fibrillation) with acute persistent vertigo 3

Optimal Imaging Strategy: Combined Approach

If both aneurysm screening AND vertigo evaluation with red flags are needed:

• Order MRI head without and with IV contrast PLUS MRA head without and with IV contrast 1
• This provides comprehensive evaluation of both parenchymal brain abnormalities (stroke, mass lesions) and vascular structures (aneurysms, dissection) 1
• MRI with diffusion-weighted imaging is superior to CT for detecting posterior circulation infarcts, which account for 70% of stroke-related dizziness 3

Critical Pitfalls to Avoid

Do not order MRI/MRA for:

• Typical BPPV with positive Dix-Hallpike and no red flags (imaging yield <1%) 1, 2, 3
• Isolated positional vertigo responding to Epley maneuver 2, 3

Do not miss:

• Approximately 10% of cerebellar strokes present identically to peripheral vestibular disorders 2
• Isolated transient vertigo may precede vertebrobasilar stroke by weeks to months 1, 2
• Normal neurologic examination does not exclude posterior circulation infarct 3

Recognize that:

• CTA head has higher specificity (>90%) than MRA for aneurysm detection but involves radiation exposure 1
• Catheter angiography remains the gold standard (>98% sensitivity and specificity) but is invasive 1
• MRA false-positives occur with vessel loops and infundibular origins 1