Mydriatic pupil as the presenting sign of common carotid artery dissection.

BACKGROUND Ipsilateral mydriasis is known to accompany signs of cerebral ischemia in unilaterally compromised carotid blood flow. Mydriasis as the presenting sign of common carotid artery (CCA) dissection has not been reported thus far. CASE DESCRIPTION We report the case of a patient who presented with a mydriatic pupil after intraoperative injury of the ipsilateral CCA. Mydriasis preceded complete third-nerve palsy and symptoms of cerebral ischemia for 12 hours. Cerebral angiography revealed occlusion of the CCA with slow collateral flow to the internal carotid artery and fetal origin of the posterior cerebral artery, suggesting a hemodynamic mechanism causing ischemia of the oculomotor nerve. Signs of cerebral ischemia and third-nerve palsy resolved completely after reconstructive surgery of the occluded vessel. CONCLUSIONS A mydriatic pupil may be the unusual first sign of compromised carotid blood flow and impending cerebral ischemia.