Carotid artery dissection revealed by an oculosympathetic spasm.

Internal carotid dissection can be responsible for stroke and lead to severe neurological and functional complications. Thus, it must be diagnosed and treated with heparin as soon as possible. Horner syndrome is one of the most usual manifestations of internal carotid dissection. We report the case of a patient who presented with a unilateral non-reactive enlargement of the right pupil that did not last longer than 30 s. As a carotid dissection was not recognized from this atypical symptomatology, magnetic resonance angiography was performed only a few days later when Horner syndrome occurred. It disclosed a dissection of the internal carotid artery ipsilateral from its origin. The evolution and the duration of the pupil involvement suggest that the initial episode of mydriasis was caused by an oculosympathetic spasm, a rare form of sympathetic dysfunction that can be observed when the sympathetic nerve or the pericarotid plexus is irritated. It is important to recognize this oculosympathetic spasm because it has equal value as Horner syndrome for the diagnosis of internal carotid dissection.