What are the next steps if an MRI (Magnetic Resonance Imaging) stroke protocol yields a false negative result?

Management of False Negative MRI Stroke Protocol

If an MRI stroke protocol yields a false negative result but clinical suspicion for stroke remains high, a delayed repeat MRI within 3-7 days is recommended as the next step. 1

Understanding False Negative MRI in Stroke

• False negative MRI results occur in approximately 5-6% of acute ischemic strokes, particularly within the first 24 hours after symptom onset 2
• Small strokes in the posterior fossa (brain stem) are most commonly missed, with up to 31% of vertebrobasilar strokes showing false-negative initial DWI within the first 24 hours 2
• DWI-MRI can still be falsely negative in approximately 50% of small ischemic strokes in the posterior fossa within the first 48 hours 1

Clinical Predictors of False Negative MRI

• Central oculomotor signs (odds ratio 2.8) and focal abnormalities on clinical examination (odds ratio 3.3) are significant predictors for lesions that may be missed on initial imaging 1
• Transient nature of symptoms is associated with a reduced risk (odds ratio 0.3) of missed lesions 1
• Combined neurological symptoms are the strongest predictor (odds ratio 16.72) of lesions that may be missed on initial MRI 1

Next Steps After False Negative MRI

Immediate Management

• Continue standard stroke care if clinical suspicion remains high despite negative imaging 1
• Consider alternative vascular imaging if not already performed:
  • CT angiography (CTA) for rapid assessment of large vessel occlusion 1
  • MR angiography (MRA) for patients with renal insufficiency or contrast allergy 1

Follow-up Imaging

• Schedule delayed MRI (3-7 days after symptom onset) which significantly improves detection of initially missed strokes 1, 3
• Consider perfusion imaging (CT or MRI) which may detect ischemia in a small proportion of DWI-negative cases 4
• For suspected posterior circulation strokes with negative initial MRI, repeat imaging is particularly important as these are most commonly missed 2

Special Considerations

• For brain stem strokes or lacunar syndromes with negative initial DWI, follow-up imaging is essential as these have higher rates of initial false negatives 4
• If hemorrhagic transformation is suspected, gradient echo sequences (T2-GRE) may be more sensitive than CT in some cases 5
• Consider stroke mimics if repeat imaging remains negative - conditions such as migraine aura, seizures, hypoglycemia, or PRES may present with stroke-like symptoms 6

Common Pitfalls to Avoid

• Ruling out stroke based solely on a negative early DWI-MRI, especially with persistent symptoms suggestive of vertebrobasilar stroke 2
• Delaying treatment decisions when clinical presentation strongly suggests stroke despite negative imaging 3
• Failing to consider alternative diagnoses when repeat imaging remains negative 6
• Overlooking the need for comprehensive vascular imaging (MRA/CTA) which may identify occlusions even when parenchymal changes are not yet visible 1