What is the likely cause and recommended acute management for a bilateral thalamic infarct involving the midbrain?

Bilateral Thalamic with Midbrain Infarct

Bilateral thalamic infarction with midbrain involvement is most commonly caused by occlusion of the artery of Percheron, and if presenting within 4.5 hours of symptom onset, should be treated with IV alteplase (0.9 mg/kg, maximum 90 mg) following standard acute ischemic stroke protocols 1.

Likely Etiology

The artery of Percheron is an anatomical variant where a single arterial trunk arising from one posterior cerebral artery supplies both paramedian thalami and sometimes the midbrain 2, 3, 4. Its occlusion produces this characteristic bilateral pattern. The primary mechanisms include:

• Arterial thromboembolism (most common): Either artery-to-artery embolism or cardiogenic sources 5
• Paradoxical embolism: Consider patent foramen ovale, especially when other sources are negative 5
• Native vessel atherosclerosis: Particularly in patients with chronic hypertension 2

Acute Management Algorithm

Immediate Assessment (Door-to-Needle Target: <60 minutes)

1. Establish time of symptom onset - when patient was last known normal 1

2. Perform rapid neurological examination - look for the classic triad:

   • Altered consciousness/somnolence
   • Vertical gaze palsy/oculomotor disorders
   • Memory impairment 4

3. Obtain emergent brain imaging:

   • Non-contrast CT initially to exclude hemorrhage 1
   • MRI with DWI is superior for diagnosis, showing bilateral paramedian thalamic hyperintensities ± midbrain involvement 2, 6
   • CT angiography or MR angiography to distinguish arterial from venous causes 7

Treatment Decision

If within 4.5 hours of onset and no contraindications:

• Administer IV alteplase per standard stroke protocol 1:
  • Dose: 0.9 mg/kg (maximum 90 mg) over 60 minutes
  • Give 10% as initial bolus over 1 minute
  • Admit to intensive care or stroke unit for monitoring 1

Bilateral thalamic arterial infarctions may be treated with thrombolysis 7. The 2018 AHA/ASA guidelines support IV alteplase for acute ischemic stroke complications of cerebral angiographic procedures and various stroke presentations, with the standard eligibility criteria applying 1.

Critical Pitfalls to Avoid

• Do not delay treatment for additional diagnostic studies if stroke mimic is suspected - the risk of symptomatic intracranial hemorrhage in mimics is quite low 1
• Do not miss the diagnosis due to initial negative imaging - early CT may be normal; MRI with DWI is more sensitive 2
• Do not overlook paradoxical embolism - obtain transesophageal echocardiography if standard workup is negative, even in elderly patients 5

Secondary Prevention Workup

After acute treatment, investigate the embolic source:

• Echocardiography (transthoracic initially, transesophageal if negative)
• 24-hour Holter monitoring
• Deep venous ultrasonography (for paradoxical embolism)
• Vascular imaging of posterior circulation 5

Initiate antiplatelet therapy and statin unless cardioembolic source identified requiring anticoagulation 5, 8.

Prognostic Considerations

Midbrain involvement is an unfavorable prognostic indicator 2. However, early diagnosis and treatment can lead to good recovery - patients may retain only mild cognitive deficits with appropriate acute intervention 8. The highly variable clinical presentation often causes diagnostic delays, making early neuroimaging vital for better outcomes 2.