Hypertension most significant modifiable risk factor for lacunar midbrain infarction
Intracranial atherosclerosis particularly prevalent in Asian and Black populations
Male sex, older age, and metabolic syndrome increase overall stroke risk
Pathophysiology
Anatomical basis of Weber syndrome
Lesion localization — ventral midbrain at level of superior colliculus
CN III fascicles traverse the ventral midbrain through the red nucleus
Cerebral peduncle carries descending corticospinal and corticobulbar tracts
Disruption of both structures produces the crossed syndrome — ipsilateral CN III palsy and contralateral hemiparesis
Vascular supply
Paramedian perforating branches of the posterior cerebral artery supply ventral midbrain
Upper basilar artery perforators also supply this territory
Occlusion of these small perforating vessels is the most common mechanism
CN III palsy mechanism
Oculomotor nerve exits the midbrain at the interpeduncular fossa
Parasympathetic fibers travel on the outer surface — compressed first by aneurysm or herniation
Pupil-sparing CN III palsy more consistent with microvascular ischemia than compressive lesion
Therapeutic Considerations
Evidence basis for treatment decisions
IV alteplase for posterior circulation stroke
EXPECTS trial 2025 demonstrated benefit of alteplase at 4.5 to 24 hours in posterior circulation ischemic stroke
Extends standard treatment window for this anatomical territory
Endovascular thrombectomy for basilar artery occlusion
ATTENTION trial demonstrated EVT superior to medical management for basilar occlusion
BAOCHE trial confirmed benefit at 6 to 24 hours
2026 AHA/ASA guideline recommends EVT for eligible basilar artery occlusion within 24 hours
Prognosis of isolated midbrain infarction
Generally favorable prognosis compared with more extensive brainstem strokes
CN III palsy may partially or fully recover over weeks to months
Bilateral involvement or basilar artery occlusion carries significantly worse prognosis
ICD-10 coding
I63.5 — cerebral infarction due to unspecified occlusion or stenosis of cerebral arteries
H49.0 — third cranial nerve palsy
Patient Discharge Instructions
copy discharge instructions
Discharge instructions for Weber syndrome
Diagnosis and medications
You were diagnosed with Weber syndrome — a type of stroke affecting the midbrain causing eye muscle weakness and limb weakness on the opposite side
Take all prescribed medications exactly as directed — do not stop aspirin or anticoagulants without speaking to your doctor
High-intensity statin therapy has been started for stroke prevention — take daily as prescribed
Activity and diet
Follow a heart-healthy low-sodium diet
No driving until cleared by your neurologist
Avoid alcohol and smoking
Attend all scheduled follow-up appointments — neurology within 1 to 2 weeks
Return to emergency department immediately for any of the following
New or worsening weakness in any limb
New or worsening drooping of the eyelid or double vision
Sudden severe headache — worst headache of your life
Difficulty speaking or understanding speech
Difficulty swallowing or choking on food or liquids
Loss of consciousness or confusion
Facial drooping
New chest pain or palpitations
References
Guidelines and Key Sources
Primary guidelines and landmark trials
2026 AHA/ASA Guideline for Early Management of Acute Ischemic Stroke — Prabhakaran S et al. Stroke 2026
Class I recommendation for IV alteplase within 4.5 hours
EVT recommended for eligible large-vessel occlusion within 24 hours
EXPECTS Trial 2025 — Yan S et al. New England Journal of Medicine 2025
Alteplase benefit for posterior circulation ischemic stroke at 4.5 to 24 hours
ATTENTION Trial — EVT versus medical management for basilar artery occlusion
BAOCHE Trial — Jovin TG et al. New England Journal of Medicine 2022
Thrombectomy 6 to 24 hours after stroke due to basilar artery occlusion
Powers WJ. Acute Ischemic Stroke. New England Journal of Medicine 2020
Comprehensive review of acute ischemic stroke management principles
Clinical Evidence Sources
Supporting clinical evidence
Bogousslavsky J et al. Pure Midbrain Infarction: Clinical Syndromes, MRI, and Etiologic Patterns. Neurology 1994
Foundational study characterizing pure midbrain infarction syndromes
Kim JS, Kim J. Pure Midbrain Infarction: Clinical, Radiologic, and Pathophysiologic Findings. Neurology 2005
Detailed characterization of clinical and imaging features; favorable prognosis for isolated midbrain infarction
Kumral E et al. Mesencephalic and Associated Posterior Circulation Infarcts. Stroke 2002
Etiology and association data for midbrain infarction
Parija S, Lalitha CS, Naik S. Weber Syndrome Secondary to Brain Stem Tuberculoma. Indian Journal of Ophthalmology 2018
Non-vascular etiology case series with management guidance
Martin PJ et al. Midbrain Infarction: Associations and Aetiologies in NEMCPCR. JNNP 1998
Markus HS et al. Posterior Circulation Ischaemic Stroke and TIA. Lancet Neurology 2013
Guo X et al. Aspiration versus stent retriever for posterior circulation stroke. CNS Neuroscience and Therapeutics 2023
Meyer L et al. Thrombectomy for Primary Distal PCA Occlusion — TOPMOST Study. JAMA Neurology 2021
Evidence & Review
Reviewed by Dr. Lucas Mastropaolo, MD, CCFP(EM) ·Last reviewed
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.