In a patient with a prior cerebrovascular accident who now presents with facial numbness, which imaging study is appropriate first: MRI brain with diffusion‑weighted imaging, MR angiography and MR venography, or non‑contrast CT brain?

MRI Brain with DWI is the Preferred Investigation

For a patient with prior stroke presenting with new facial numbness, obtain an MRI brain with diffusion-weighted imaging (DWI) as the first-line investigation to detect acute ischemia. Add MR angiography (MRA) and MR venography (MRV) to evaluate for vascular stenosis, occlusion, or venous thrombosis that could explain recurrent symptoms 1, 2.

Rationale for MRI Over CT

MRI with DWI is superior to CT for detecting acute ischemic changes, particularly in the early hours when symptoms first appear. DWI is highly sensitive and specific for acute cerebral ischemia and can confirm the vascular origin of new neurological deficits 2, 3. In a patient with prior stroke, distinguishing new ischemia from old infarct is critical—DWI shows restricted diffusion in acute lesions while old strokes appear as chronic changes on conventional sequences 4.

CT brain without contrast has limited utility in this scenario unless you need to:

• Rule out hemorrhagic conversion urgently (if the patient is unstable or deteriorating rapidly)
• Exclude mass effect or herniation as complications
• Work around MRI contraindications (pacemaker, severe claustrophobia, metallic implants) 1

CT is less sensitive than MRI for detecting early ischemic changes and provides minimal information about the underlying vascular pathology causing recurrent symptoms 3, 5.

Why Add MRA and MRV

The 2024 ACR Appropriateness Criteria emphasize vascular imaging in patients with prior stroke presenting with new symptoms 1. Specifically:

• MRA of head and neck identifies intracranial atherosclerosis, carotid stenosis, or arterial occlusion that increases stroke recurrence risk
• MRV excludes cerebral venous thrombosis, which can present with focal neurological symptoms including facial numbness and mimics arterial stroke 6

Current guidelines recommend noninvasive cervical carotid imaging within 24-48 hours for patients with minor stroke who are candidates for intervention, given the high early risk of recurrent stroke with symptomatic carotid stenosis 1.

Clinical Algorithm

1. Obtain MRI brain with DWI + MRA head/neck + MRV as the comprehensive first study
2. Look for:
   • Restricted diffusion on DWI indicating acute infarct
   • Vascular stenosis/occlusion on MRA
   • Venous thrombosis on MRV
3. Reserve CT brain without contrast only if:
   • MRI is contraindicated or unavailable
   • Patient is unstable and you need rapid hemorrhage exclusion
   • Concern for acute hemorrhagic conversion requiring immediate assessment 1

Common Pitfalls

• Don't use CT with contrast—it paradoxically causes confusion by enhancing subacute infarcts, mimicking hemorrhagic conversion or aggressive lesions 1
• Don't delay vascular imaging—the etiology matters urgently because symptomatic carotid stenosis carries high early recurrence risk
• Don't assume old stroke explains new symptoms—facial numbness could represent new ischemia in a different vascular territory, venous thrombosis, or progression of underlying atherosclerotic disease 2

The combination of DWI (for acute tissue injury), MRA (for arterial pathology), and MRV (for venous pathology) provides the most complete evaluation to guide urgent management decisions and prevent recurrent events 1, 2.