Which among the following is wrong regarding Weber’s syndrome?

Explanation

## Correct Answer: D. Ipsilateral paralysis of lower face Weber's syndrome is a midbrain stroke syndrome characterized by ipsilateral oculomotor nerve (CN III) palsy combined with contralateral motor signs. The discriminating fact is that facial weakness in Weber's syndrome is **contralateral and affects the lower face**, not ipsilateral. This occurs because the corticobulbar tract to the lower face has bilateral innervation from the motor cortex, but the upper face receives bilateral input while the lower face receives primarily contralateral input. In Weber's syndrome, the lesion is in the ventromedial midbrain affecting the cerebral peduncle (containing corticospinal and corticobulbar tracts) and the oculomotor nerve fascicles. The ipsilateral CN III palsy causes ptosis, mydriasis, and impaired eye movements. The contralateral hemiplegia results from corticospinal tract involvement. Contralateral parkinsonism occurs due to involvement of the substantia nigra or its connections. However, facial weakness is contralateral (lower face predominantly) due to the crossed nature of the corticobulbar pathway for lower facial muscles. Ipsilateral lower facial paralysis would indicate a facial nerve (CN VII) lesion, which is NOT part of Weber's syndrome. This is a classic brainstem syndrome tested frequently in Indian medical examinations and requires precise anatomical understanding of midbrain pathology. ## Why the other options are wrong **A. Contralateral parkinsonism** — This is a recognized feature of Weber's syndrome. Involvement of the substantia nigra or its efferent connections in the ventromedial midbrain can cause contralateral parkinsonian features (rigidity, bradykinesia, tremor). This is a well-documented clinical finding in midbrain infarction and is therefore correct, not wrong. **B. Ipsilateral oculomotor nerve palsy** — This is the hallmark of Weber's syndrome. The oculomotor nerve fascicles pass through the ventromedial midbrain and are damaged ipsilateral to the lesion, causing CN III palsy with ptosis, mydriasis, and impaired adduction/elevation. This is a defining feature and is therefore correct, not wrong. **C. Contralateral hemiplegia** — This is a cardinal feature of Weber's syndrome. The corticospinal tract in the cerebral peduncle is damaged, causing contralateral hemiplegia (weakness of arm and leg). This crossed motor deficit is a defining characteristic of the syndrome and is therefore correct, not wrong. ## High-Yield Facts - **Weber's syndrome** = ipsilateral CN III palsy + contralateral hemiplegia + contralateral parkinsonism (ventromedial midbrain lesion) - **Facial weakness in Weber's** is contralateral (lower face > upper face) due to crossed corticobulbar tract, NOT ipsilateral CN VII involvement - **CN III palsy signs**: ptosis, mydriasis, 'down and out' eye, impaired adduction and elevation - **Contralateral parkinsonism** occurs from substantia nigra or its connection involvement in midbrain infarction - **Corticospinal tract** in cerebral peduncle causes contralateral hemiplegia in Weber's syndrome ## Mnemonics **Weber's Syndrome Triad** **CN3 + Hemi + Parkinson** — Ipsilateral oculomotor nerve palsy, Contralateral hemiplegia, Contralateral parkinsonism (all from ventromedial midbrain lesion) **Remember: Facial weakness is CROSSED in Weber's** **Contralateral lower face** (not ipsilateral) because corticobulbar tract is crossed for lower facial muscles; ipsilateral facial weakness = CN VII lesion (not Weber's) ## NBE Trap NBE pairs Weber's syndrome with ipsilateral facial weakness to trap students who confuse brainstem motor pathway anatomy (crossed corticobulbar tract for lower face) with cranial nerve lesions (CN VII). The syndrome involves CN III ipsilaterally, but motor deficits are contralateral. ## Clinical Pearl In Indian stroke units, Weber's syndrome is a classic presentation of midbrain infarction from vertebrobasilar disease. The key bedside finding is the **"down and out" eye with contralateral weakness** — recognizing that facial weakness is contralateral (not ipsilateral) helps differentiate Weber's from other brainstem syndromes like Foville's or Millard-Gubler syndrome, which involve CN VII directly. _Reference: Harrison Ch. 381 (Brainstem Syndromes); Robbins Ch. 28 (CNS Pathology)_