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Isolated Medial Longitudinal Fasciculus Midbrain Infarction Mimicking Medial Rectus Paralysis
Minli Yan1, Jiayi Liu2, Zhengxiang Zhang1
1Department of Neurology, The First Affiliated Hospital, Zhejiang Chinese Medical University (Zhejiang Provincial Hospital of Traditional Chinese Medicine).
Introduction:
Medial longitudinal fasciculus infarction is rare in clinical practice and generally accompanied by brain tissue damage around the medial longitudinal fasciculus. Isolated medial longitudinal fasciculus midbrain infarction was seldom reported.
Case Report:
An 81-year-old man with hypertension was admitted to our hospital because of sudden onset diplopia. A neurological examination revealed right adduction paresis without abducting nystagmus in the left eye, whereas the convergence reflex was normal. Diffusion-weighted magnetic resonance imaging demonstrated a small acute lacunar medial longitudinal fasciculus infarction in the right midbrain at the level of the inferior colliculus. Diffusion-tensor imaging showed a reduction of the right medial longitudinal fasciculus. Medial longitudinal fasciculus infarction is rare and occurs most commonly in the pons. The authors report on a case of isolated medial longitudinal fasciculus infarction that was diagnosed because of sudden diplopia and manifested as simple internal rectus paralysis with no abducting nystagmus on the contralateral side of the lesion.
Conclusion:
Isolated midbrain-medial longitudinal fasciculus infarction without contralateral abducting nystagmus is a rare occurrence. It can be differentiated from partial oculomotor palsy by assessing the convergence reflex, primary gaze, and diffusion-tensor imaging.
Insights
Isolated medial longitudinal fasciculus (MLF) infarction in the midbrain is rare. This case highlights its presentation as diplopia and internal rectus paralysis, distinguishable from oculomotor palsy using specific clinical and imaging assessments.
Area of Science:
- Neuroscience
- Neurology
- Neuroimaging
Background:
- Medial longitudinal fasciculus (MLF) infarction is uncommon and typically involves surrounding brain tissue.
- Isolated infarction of the MLF within the midbrain is exceptionally rare in clinical reports.
Observation:
- An 81-year-old male with hypertension presented with sudden onset diplopia.
- Neurological examination revealed right adduction paresis and normal convergence, with no abducting nystagmus in the left eye.
Findings:
- Diffusion-weighted MRI confirmed a small, acute lacunar MLF infarction in the right midbrain.
- Diffusion-tensor imaging indicated reduced integrity of the right MLF, distinguishing it from partial oculomotor nerve palsy.
Implications:
- This case underscores the rarity of isolated midbrain MLF infarction.
- Clinical assessment of convergence reflexes and primary gaze, alongside diffusion-tensor imaging, aids in differentiating this condition from oculomotor palsy.
