What is the next step in managing an acute patient with right upper‑motor‑neuron facial palsy, right hemiplegia, and a normal non‑contrast head CT?

Acute Stroke Management: MRI Brain with Diffusion-Weighted Imaging

In a patient with right UMN facial palsy and right hemiplegia but normal non-contrast head CT, proceed immediately to MRI brain with diffusion-weighted imaging (DWI) to detect acute ischemia that CT has missed. 1, 2

Why CT is Insufficient in This Case

• Non-contrast CT significantly underestimates acute ischemia, particularly in the first 6 hours when early infarct signs may be subtle or absent 2
• CT has limited sensitivity for detecting small brainstem infarcts due to beam hardening artifact in the posterior fossa 1, 2
• Up to 70% of strokes presenting with altered mental status or atypical features are missed on initial CT 3
• The combination of UMN facial palsy with hemiplegia strongly suggests cortical or subcortical stroke, which may not be visible on CT in the hyperacute phase 1, 2

The Diagnostic Imperative: MRI with DWI

MRI with diffusion-weighted imaging is 30% more sensitive than CT for detecting acute ischemic stroke and should be obtained immediately when CT is normal but clinical suspicion remains high. 1, 2

• DWI detects acute ischemia within minutes of symptom onset, well before CT changes appear 1, 2
• MRI changed clinical management in 76% of patients with acute neurological deficits and negative CT, including revised diagnoses in 20% 3
• The American Heart Association/American Stroke Association guidelines specifically recommend MRI when CT is unrevealing but stroke remains clinically suspected 1

Vascular Imaging is Equally Critical

Add MR angiography (MRA) or CT angiography (CTA) immediately to identify large vessel occlusion requiring mechanical thrombectomy. 1, 4

• Isolated central facial palsy with hemiplegia is associated with flow-limiting thromboembolic middle cerebral artery (MCA) disease in 78% of cases, not just lacunar infarcts 4
• Comprehensive vascular imaging is essential because patients with isolated facial weakness may harbor proximal MCA occlusions amenable to endovascular therapy 4
• Mechanical thrombectomy for large vessel occlusion is recommended and can be performed up to 24 hours from symptom onset in selected patients 1

Critical Pitfall: Don't Assume Lacunar Stroke

• Traditional teaching suggests isolated facial palsy indicates a small lacunar infarct in the corona radiata or pons 4
• However, 78% of patients presenting with isolated central facial palsy actually have flow-limiting MCA disease requiring urgent intervention 4
• This misconception leads to delayed or missed opportunities for mechanical thrombectomy 4

Alternative Diagnosis to Exclude: Lateral Medullary Syndrome

• If the patient has additional features like Horner's syndrome, ataxia, or crossed sensory findings, consider lateral medullary (Wallenberg) syndrome 5
• This posterior circulation stroke can present with ipsilateral UMN facial palsy and contralateral hemiparesis when the infarction extends caudally to involve pyramidal tracts 5
• Posterior fossa strokes are particularly difficult to detect on CT due to beam hardening artifact 1, 2

Practical Management Algorithm

1. Immediate MRI brain without and with contrast including DWI, FLAIR, and gradient echo sequences 1, 2
2. Concurrent MRA head and neck (or CTA if MRI contraindicated) to evaluate for large vessel occlusion 1, 4
3. If large vessel occlusion identified: Activate interventional neuroradiology for mechanical thrombectomy consideration 1
4. If MRI confirms acute ischemia without large vessel occlusion: Proceed with standard acute ischemic stroke management including antiplatelet therapy and risk factor modification 1
5. If MRI remains negative but symptoms persist or worsen: Consider alternative diagnoses including seizure with Todd's paralysis, though progressive improvement would be expected 6

Time-Sensitive Considerations

• Brain imaging evaluation should be completed within 25 minutes of arrival for thrombolysis-eligible patients 1
• Do not delay MRI acquisition while waiting for "CT changes to develop"—this outdated approach misses the therapeutic window 1, 2
• Neurological consultation should be obtained immediately for any acute neurological change 1