Case Report/Case SeriesIsolated Medial Longitudinal Fasciculus Midbrain Infarction Mimicking Medial Rectus ParalysisYan, Minli MD*; Liu, Jiayi MD†; Zhang, Zhengxiang MD*Author Information *Department of Neurology, The First Affiliated Hospital, Zhejiang Chinese Medical University (Zhejiang Provincial Hospital of Traditional Chinese Medicine) †The First School of Clinical Medicine, Zhejiang Chinese Medical University, Hangzhou, China The authors declare no conflicts of interest. Correspondence to: Zhengxiang Zhang, MD, Department of Neurology, The First Affiliated Hospital of Zhejiang Chinese Medical University (Zhejiang Provincial Hospital of Traditional Chinese Medicine), 54 Youdian Street, Hangzhou 310006, China. E-mail: [email protected]. The Neurologist: March 2021 - Volume 26 - Issue 2 - p 66-68 doi: 10.1097/NRL.0000000000000302 Buy Metrics Abstract 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. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.