Unilateral midbrain infarction causing upward and downward gaze palsy

Area of Science:

• Neuroscience
• Ophthalmology
• Neurology

Background:

• Vertical gaze disorders, including loss of vertical saccades and smooth pursuit, can result from lesions in the midbrain.
• Previous cases of bidirectional vertical gaze palsy often involved the posterior commissure or bilateral lesions of the rostral interstitial nucleus of the medial longitudinal fasciculus.

Observation:

• A 47-year-old woman presented with sudden, complete loss of vertical saccades, smooth pursuit, and vestibular eye movements.
• Magnetic Resonance Imaging (MRI) revealed a unilateral infarct in the midbrain, specifically affecting the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and the interstitial nucleus of Cajal (INC).
• The posterior commissure (PC) remained unaffected by the infarct.

Findings:

• The unilateral midbrain lesion, involving the riMLF and INC but sparing the PC, is presumed to have disrupted vertical gaze pathways before decussation.
• This resulted in an anatomically unilateral lesion that produced a functionally bilateral deficit in vertical eye movement control.
• This case is the first to demonstrate that a unilateral lesion of the riMLF and INC, without PC involvement, can cause complete bidirectional vertical gaze palsy.

Implications:

• This finding expands our understanding of the neuroanatomy underlying vertical eye movement control.
• It suggests that unilateral lesions in specific midbrain structures can have widespread functional consequences on gaze.
• The study highlights the critical role of the riMLF and INC in coordinating vertical eye movements and provides insights for diagnosing and treating gaze abnormalities.