INTRODUCTION: Acute oculomotor nerve (CN III) palsies are commonly attributed to microvascular disease or compressive lesions and aneurysms, but may rarely be associated with ischemic large vessel disease. We report a case of an extracranial internal carotid artery (ICA) dissection heralded by CN III palsy with review of the relevant literature.

CASE REPORT: A 24-year-old right-handed man presented with right-sided weakness preceded by vomiting 2 days earlier. The following day, the family noted his left eye to be deviated outward with enlarged pupil and droopy eyelid. On the day of admission, he had a fall owing to right-sided weakness. His neurological examination revealed significant aphasia, left third nerve palsy, right homonymous hemianopsia, and right-sided hemiplegia with hemisensory deficits. A brain magnetic resonance image showed an acute ischemic infarct in the left middle cerebral artery distribution without mass effect. Magnetic resonance angiogram showed a left extracranial internal cerebral artery (ICA) dissection with absence of flow within the distal cervical and intracranial ICA segments. He underwent a decompressive left hemicraniectomy with partial improvement in his deficits.

DISCUSSION: Oculomotor nerve palsy as a result of ICA disease is a rare entity but has been reported in cases of stenosis, occlusion, and dissection. It is likely to be caused by hypoperfusion of CN III secondary to low flow or microembolism in the arteries feeding the nerve. The risk of CN III palsy in patients with ICA disease is higher in the presence of a fetal posterior cerebral artery.

CONCLUSIONS: Acute oculomotor nerve palsies with pupillary involvement warrant thorough investigation. When routine work-up fails to elucidate an etiology, extracranial carotid pathology should be considered.