How is the localization of a stroke determined and what are the treatment options?

Stroke Localization and Treatment Options

The localization of a stroke is primarily determined through neuroimaging techniques, with non-contrast CT being the initial recommended imaging modality to distinguish between ischemic and hemorrhagic stroke, followed by vascular imaging to identify the site of occlusion and guide treatment decisions. 1, 2

Neuroimaging for Stroke Localization

Initial Imaging

• Non-contrast CT is the most commonly used initial imaging modality due to its speed, availability, and ability to rule out hemorrhage, though it has lower sensitivity for small or posterior fossa lesions 1, 2
• Brain imaging must be performed within 30 minutes of hospital admission to guide hyperacute care decisions 2
• For patients within 3 hours of symptom onset, vascular imaging is indicated during the initial evaluation if it doesn't delay administration of intravenous tPA 1

Advanced Imaging

• Diffusion-weighted MRI (DWI) is the most sensitive and specific technique for detecting acute ischemic stroke, with sensitivity of 88-100% and specificity of 95-100% 3
• For patients beyond 3 hours from symptom onset, either MR-DWI or CTA-SI should be performed along with vascular imaging and perfusion studies, particularly if mechanical thrombectomy or intra-arterial thrombolytic therapy is being considered 1
• CT angiography (CTA) of both extracranial and intracranial vessels helps identify large vessel occlusions and guide treatment decisions 2

Imaging Interpretation

• The distribution of infarcts on imaging is crucial for determining stroke etiology:
  • Multiple, scattered lesions in different vascular territories suggest embolic source 4
  • Watershed distribution suggests thrombotic stroke from hypoperfusion 4
• The ASPECTS (Alberta Stroke Program Early CT Score) can be used to estimate the extent of early ischemic changes on CT, with scores ≤7 indicating poor clinical outcome 5

Clinical Assessment for Localization

• The National Institutes of Health Stroke Scale (NIHSS) should be used to determine stroke severity and monitor for evolving changes 1, 6
• Clinical features can suggest specific vascular territories:
  • Middle cerebral artery: hemiparesis, hemihypesthesia, aphasia, spatial neglect 3
  • Posterior circulation: vertigo, ataxia, diplopia, dysarthria 3
  • Subcortical areas: pure motor weakness, ataxic hemiparesis 3
• For patients with cerebellar symptoms, the HINTS (head-impulse, nystagmus, test of skew) examination is more sensitive for cerebellar stroke than early MRI 6

Treatment Options Based on Localization

Intravenous Thrombolysis

• For patients within 4.5 hours of last known well, intravenous recombinant tissue plasminogen activator (rtPA) is the standard treatment 6
• Patients with NIHSS scores ≥20 have a 17% risk of intracranial hemorrhage with rtPA, compared to 3% risk for those with scores <10 1
• Advanced imaging techniques can extend the treatment window to 9 hours in selected patients 6

Endovascular Treatment

• For large vessel occlusions identified on vascular imaging, mechanical thrombectomy should be considered 1, 2
• Patients presenting within 24 hours of last known well should undergo cerebrovascular imaging to assess benefits of endovascular interventions 6
• Proximal large-vessel occlusions may respond better to intra-arterial thrombolysis or mechanical thrombectomy than to intravenous thrombolysis 1

Post-Stroke Evaluation

• Once initial interventions have been implemented, additional evaluations should be performed to determine stroke etiology:
  • Cardiac assessment: ECG for all patients; echocardiography for selected cases 2
  • Vascular imaging: carotid imaging for anterior circulation strokes 6
  • Extended cardiac monitoring: to detect occult atrial fibrillation in seemingly cryptogenic strokes 4

Common Pitfalls and Caveats

• Delaying treatment for advanced imaging must be balanced against the time-sensitive nature of reperfusion therapies ("time is brain") 2, 5
• Relying solely on clinical features without imaging is insufficient for accurate stroke localization 4
• CT is relatively insensitive in detecting acute and small cortical or subcortical infarctions, especially in the posterior fossa 1
• Approximately 25% of ischemic strokes remain of uncertain etiology despite adequate investigation 4
• The presence of microbleeds on MRI gradient-echo sequences is not a contraindication to intravenous tPA within 3 hours of stroke onset in patients with a small number of microbleeds, though the risk in patients with multiple microbleeds (>5) is uncertain 1