One-and-a-half syndrome is caused by a lesion at which location?
- A Unilateral damage to the paramedian pontine reticular formation (PPRF) and the ipsilateral MLF ✓
- B Bilateral MLF lesions at the level of the pons
- C Ipsilateral abducens nucleus plus contralateral MLF
- D Rostral interstitial nucleus of the MLF (riMLF) bilaterally
Correct answer: A. Unilateral damage to the paramedian pontine reticular formation (PPRF) and the ipsilateral MLF
Explanation
One-and-a-half syndrome results from a single lesion in the pons that destroys both the ipsilateral PPRF (eliminating ipsilateral conjugate gaze — the 'one') and the ipsilateral internuclear fibre in the MLF (eliminating ipsilateral adduction during contralateral gaze — the 'half'). The only remaining horizontal eye movement is abduction of the contralateral eye. The lesion is classically caused by pontine infarction or MS. Bilateral MLF lesions cause bilateral INO without full conjugate gaze loss.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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