A patient with a midbrain tegmental lesion shows loss of vertical gaze upward, convergence-retraction nystagmus on attempted upgaze, and light-near dissociation of pupils. Which nucleus is specifically damaged?
- A Rostral interstitial nucleus of MLF (riMLF) and posterior commissure ✓
- B Abducens nucleus
- C Trochlear nucleus
- D Frontal eye fields
Correct answer: A. Rostral interstitial nucleus of MLF (riMLF) and posterior commissure
Explanation
Parinaud syndrome (dorsal midbrain syndrome) results from compression or infarction of the pretectal area and superior colliculus, specifically damaging the rostral interstitial nucleus of the MLF (riMLF) and posterior commissure. The riMLF is the vertical gaze centre; posterior commissure damage impairs upgaze and produces the characteristic light-near dissociation because the near reflex fibres bypass the damaged pretectum. Abducens nucleus controls horizontal gaze; the trochlear nucleus innervates the superior oblique.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.