How to Order Brain MRI for History of CVA and Family History of Aneurysm
Order an MRI head without IV contrast combined with MRA head without IV contrast as your primary imaging study 1. This combination provides both parenchymal brain assessment for prior stroke sequelae and vascular screening for potential aneurysms in this at-risk patient.
Recommended Imaging Protocol
Primary Study: Combined MRI/MRA Head Without Contrast
- MRI head without IV contrast (Rating: 6/9 - "may be appropriate") 1
- MRA head without IV contrast (Rating: 8/9 - "usually appropriate") 1
The MRA without contrast is specifically designated as the "ideal screening study of choice" for patients at risk of unruptured aneurysm, which includes those with family history of subarachnoid hemorrhage 1. This applies to patients who have at least two first-degree relatives with history of SAH, though screening may be considered with even one affected first-degree relative, particularly a sibling 2.
Why This Combination Works
For the CVA history component:
- MRI is more sensitive than CT for detecting prior infarcts, encephalomalacia, and chronic cerebrovascular changes 1
- Non-contrast sequences adequately demonstrate old stroke territory and white matter disease
- Provides baseline documentation of existing vascular injury
For the aneurysm screening component:
- MRA without contrast has 95% pooled sensitivity and 89% specificity for detecting intracranial aneurysms 3
- Avoids radiation exposure (important for potential serial screening)
- No contrast allergy or renal function concerns
- Suitable for detecting clinically significant aneurysms (≥3-5mm) 4, 5
Alternative Options Based on Clinical Context
If MRI is contraindicated or unavailable:
Order CTA head with IV contrast (Rating: 8/9 - "usually appropriate") 1
- CTA has similar sensitivity but higher specificity than MRA for aneurysm detection 1
- Can be performed quickly
- Better for confirming MRA findings if needed
- Superior for aneurysms adjacent to bone
Consider adding contrast to MRI if:
MRA head without and with IV contrast (Rating: 8/9 - "usually appropriate") 1
- Only if dynamic imaging is specifically needed
- Generally adds minimal benefit for screening purposes 6
Important Clinical Caveats
Limitations of Non-Invasive Screening
- Small aneurysms (<3-5mm): Both MRA and CTA have reduced sensitivity 3, 4, 5
- False positives: MRA may overcall normal vascular variants (infundibula, vessel loops) 3
- Aneurysms near bone: MRA may miss these; CTA is superior in this location 3
When to Consider Catheter Angiography
If non-invasive imaging shows suspicious findings or if the patient has:
- Multiple first-degree relatives with SAH (particularly siblings) 2
- Polycystic kidney disease 1, 2
- Prior treated aneurysm 1
Catheter angiography remains the gold standard (Rating: 9/9) but is reserved for definitive evaluation, not initial screening 3.
Screening Interval Considerations
- If initial screening is negative, there remains risk of new aneurysm formation over time 2
- Repeat screening may be warranted, though optimal intervals are not clearly established 2
- The rupture rate of small asymptomatic aneurysms is relatively low (0.05-0.5% per year depending on size and prior SAH history) 7
What NOT to Order
Avoid these studies for this indication:
- CT head without contrast alone (Rating: 3/9) - inadequate for aneurysm screening 1
- MRI head with contrast alone without MRA - misses the vascular screening component
- US transcranial Doppler - insufficient for aneurysm detection
- Neck vessel imaging alone - doesn't address intracranial aneurysm risk
Practical Ordering Language
"MRI brain without contrast with MRA head without contrast for evaluation of prior CVA and screening for intracranial aneurysm given family history of aneurysm/SAH"
This combined study efficiently addresses both clinical concerns in a single imaging session without requiring IV contrast, making it the most appropriate and cost-effective initial approach.