A 37-year-old Asian nonsmoking man with no known medical or drug history presented with an insidious onset of left-eye ptosis (only brought to attention by his friends on review of recent photographs) and subsequent painless vertical diplopia for 1 year. He did not complain of headaches, facial numbness, dysarthria, facial droop, dysphagia, or limb weakness or numbness. There was no history of joint pain or constitutional symptoms.
Neurological examination revealed a nonfatigable partial left-eyelid ptosis, left-eye hypotropia at primary position, and impaired left eye supraduction (Figure 1) with a nonreactive left pupil on direct and consensual light reflexes. There were no other cranial nerve deficits. Limb reflexes, motor testing, and sensory testing results were normal, and the plantar responses were flexor.
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D. Neurovascular conflict of the oculomotor nerve
Further detailed MRI constructive interference in steady-state sequence with fine cuts of the midbrain was performed, which revealed that the left posterior cerebral artery (PCA) and left superior cerebellar artery (SCA) were indenting the oculomotor nerve with resultant displacement (Figure 2). No intracranial aneurysms were demonstrated.
An oculomotor nerve palsy with pupil involvement is often due to extrinsic compression by posterior communicating artery (PCoA) aneurysms.1 This is because when the nerve exits the midbrain, its cisternal course2 passes between the PCA and SCA and is accompanied by the PCoA before running in an anteromedial-lateral direction to reach the cavernous sinus. The dilated pupil occurs as external compression affects the pial vessels, which then compromise the parasympathetic fibers and results in paralysis of the sphincter pupillae.
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CME Disclosure Statement: Unless noted, all individuals in control of content reported no relevant financial relationships. If applicable, all relevant financial relationships have been mitigated.
Corresponding Author: Newman Cheng, MBBS (S’pore), MRCP (UK), MRCP(UK) (Neurology), National Neuroscience Institute (SGH Campus), 20 College Rd, Academia, Singapore S169856 (firstname.lastname@example.org).
Published Online: October 3, 2022. doi:10.1001/jamaneurol.2022.3149
Correction: This article was corrected on November 14, 2022, to fix a typographical error in the figure 2 caption.
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient for granting permission to publish this information.
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