Bilateral internal carotid artery dissection presenting as isolated unilateral Horner syndrome.

A 52-year-old man developed a unilateral Horner syndrome following a skiing accident. He was otherwise asymptomatic. Neuroimaging with magnetic resonance revealed bilateral internal carotid artery dissections, and he was urgently treated with anticoagulation. Immediate neuroimaging should be performed in any patient with Horner syndrome following trauma, regardless of other symptoms or signs.