A 50-year-old male with a history of type 2 diabetes, dyslipidemia, hypertension, chronic kidney disease, prior tobacco use, and alcohol dependence awoke with binocular oblique diplopia. The diplopia impaired his depth perception, making it unsafe to continue working as a welder.

Neuro-ophthalmologic examination revealed a right head tilt and right hyperphoria, which worsened on left/down gaze and on right head tilt - findings consistent with a right superior oblique dysfunction. These signs localize either to the right fourth cranial nerve or the left trochlear nucleus.

Orbit MRI was normal. Brain MRI demonstrated a 2-mm punctate lesion with diffusion restriction and corresponding low ADC signal in the left dorsal midbrain, adjacent to the periaqueductal gray at the level of the inferior colliculus – precisely where the left trochlear nucleus resides. MR angiogram of the head and neck was normal.

The patient’s symptoms improved spontaneously and were nearly resolved 5 weeks after diplopia onset, consistent with a microvascular infarct of the left trochlear nucleus. He was able to safely return to work.

This case highlights the importance of detailed neuro-ophthalmologic evaluation in the localization and diagnosis of isolated trochlear nuclear stroke.  Although rare and often mimicking peripheral cranial nerve palsy, early recognition enables timely implementation of secondary stroke prevention strategies and may reduce the risk of future cerebrovascular events.