Weber's Syndrome

Overview

Weber's syndrome, also known as superior alternating hemiplegia, is a rare neurological condition resulting from a stroke or infarction in the midbrain, specifically affecting the cerebral peduncle and the oculomotor nerve (cranial nerve III). It is a type of brainstem stroke syndrome characterized by a combination of ipsilateral oculomotor nerve palsy and contralateral hemiparesis or hemiplegia. The condition is typically caused by an occlusion of branches of the posterior cerebral artery and presents with distinct clinical signs due to the involvement of both motor and cranial nerve pathways. Prompt diagnosis and management are essential to improve neurological outcomes.

Causes

Weber’s syndrome is most commonly caused by a vascular insult, particularly an infarction in the midbrain region due to:

• Occlusion of the posterior cerebral artery (PCA): Especially its penetrating branches that supply the medial midbrain, including the cerebral peduncle and oculomotor nerve fibers.

• Embolic or thrombotic stroke: Often related to atherosclerosis, hypertension, or cardiac disease.

• Other less common causes: These include vascular malformations, tumors compressing the midbrain, or traumatic injury.

The condition results from damage to two critical structures:

1. The oculomotor nerve (CN III), which controls eye movements and pupil constriction.

2. The corticospinal tract within the cerebral peduncle, responsible for voluntary motor control on the opposite side of the body.

Symptoms

Weber’s syndrome presents with a classic combination of neurological signs due to the involvement of the oculomotor nerve and the corticospinal tract. The hallmark features include:

• Oculomotor nerve palsy (ipsilateral to the lesion):

  • Ptosis (drooping of the upper eyelid)

  • Diplopia (double vision) due to impaired extraocular movements

  • Eye turned "down and out" due to unopposed action of lateral rectus and superior oblique muscles

  • Mydriasis (dilated pupil) with loss of pupillary light reflex

• Contralateral hemiparesis or hemiplegia:

  • Weakness or paralysis of the arm and leg on the opposite side of the lesion

  • May also involve facial weakness if the corticobulbar tract is affected

• Additional symptoms: Depending on the extent of midbrain involvement, symptoms such as dysarthria, dysphagia, or ataxia may also occur.

Diagnosis

Diagnosis of Weber’s syndrome is based on clinical findings and confirmed through neuroimaging. Key diagnostic steps include:

• Neurological examination: Identifies the classic pattern of cranial nerve III palsy with contralateral motor deficits.

• Magnetic Resonance Imaging (MRI): Especially diffusion-weighted imaging (DWI), is the most sensitive method to detect acute infarction in the midbrain region.

• Magnetic Resonance Angiography (MRA) or CT Angiography: Used to visualize vascular occlusions or stenosis in the posterior circulation.

• Blood tests and cardiac evaluation: To identify underlying risk factors such as hyperlipidemia, atrial fibrillation, or hypercoagulable states.

Weber's syndrome must be distinguished from other midbrain syndromes such as Claude’s syndrome, Benedikt’s syndrome, and Parinaud’s syndrome, which affect different structures within the brainstem.

Treatment

Treatment of Weber's syndrome focuses on addressing the underlying vascular cause, managing symptoms, and initiating rehabilitation. Management strategies include:

• Acute stroke treatment:

  • Thrombolytic therapy (e.g., tPA) if the patient presents within the therapeutic window for ischemic stroke.

  • Antiplatelet agents (aspirin or clopidogrel) for secondary prevention.

  • Anticoagulation in patients with cardioembolic stroke due to atrial fibrillation.

• Neuroprotective measures: Maintaining optimal blood pressure, glucose levels, and oxygenation.

• Symptom-specific treatments:

  • Eye patch or prism glasses for diplopia

  • Physical and occupational therapy for motor weakness

  • Speech therapy if bulbar symptoms are present

• Long-term risk factor management: Control of hypertension, diabetes, lipid levels, and lifestyle modifications (e.g., smoking cessation, healthy diet).

Prognosis

The prognosis of Weber’s syndrome varies depending on the severity of the stroke and the timing of intervention. Early treatment can improve outcomes and reduce the risk of permanent disability. Some patients may recover partially or fully with rehabilitation, especially if the infarction is limited in size. However, significant damage to the midbrain structures may result in long-term neurological deficits, including persistent weakness or cranial nerve dysfunction. Mortality is generally low unless the stroke is part of a larger posterior circulation event. Regular follow-up and rehabilitation are crucial to maximize functional recovery and prevent recurrent strokes.