A 58-year-old man suddenly develops right-sided hemiplegia with ipsilateral third nerve palsy and contralateral loss of proprioception in the arm. The lesion is located in the:

• A Right medial medulla
• B Right pontine tegmentum
• C Right crus cerebri (midbrain basis pedunculi) ✓
• D Right paramedian thalamus

Explanation

Weber's syndrome results from a lesion in the basis pedunculi (crus cerebri) of the midbrain. It involves the corticospinal fibres passing through the crus and the emerging fibres of CN III, producing ipsilateral III palsy with contralateral hemiplegia. The medial medulla produces XII palsy with contralateral hemiplegia (medial medullary or Dejerine syndrome). The pontine tegmentum would implicate CN VI/VII.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.