Introduction
- Weber syndrome first described by Hermann Weber in a 52-year-old male with left third nerve palsy and right hemiplegia due to a bleed in the left cerebral peduncle.
- It is a midbrain stroke syndrome, also called superior alternating hemiplegia.
- Characterized by ipsilateral third nerve palsy and contralateral hemiparesis.
- Commonly due to occlusion of a branch of the posterior cerebral artery.
- Oculomotor nerve arises from two nuclei:
- Main motor nucleus: controls extraocular muscles (except lateral rectus and superior oblique) and levator palpebrae superioris.
- Accessory parasympathetic nucleus (Edinger-Westphal): controls pupil constriction and lens accommodation.
Etiology
- Caused by lesions in the ventromedial midbrain.
- Blood supply to midbrain: paramedian mesencephalic branches (basilar), peduncular perforating branches (posterior cerebral artery), superior cerebellar artery, choroidal arteries.
- Common causes: infarctions of paramedian and peduncular perforators.
- Less common causes: hemorrhage, aneurysms, tumors, demyelinating diseases.
- Associated risk factors: hypertension, diabetes, hypercholesterolemia.
- Isolated midbrain infarction is rare (7.6%) and often occurs with other vertebrobasilar infarcts.
- Causes of infarction (in descending order): cardioembolism, in situ thrombosis, large artery embolism, intrinsic perforator branch disease.
Epidemiology
- Exact incidence unknown; typically occurs with other posterior circulation infarcts.
- One study: isolated midbrain infarction in only 0.7% of posterior circulation strokes.
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