Transient Pourfour du Petit Syndrome as the Presenting Sign of Internal Carotid Artery Aneurysm

Pourfour du Petit syndrome (PdPS) is a rare oculosympathetic hyperactivity syndrome characterized by ipsilateral mydriasis, eyelid retraction, and hyperhidrosis. We report a case of a 36-year-old female who presented to the emergency department with a chief complaint of a dilated pupil with photosensitivity and blurred vision in the left eye (OS). On examination, the best corrected visual acuity was 20/20 in both eyes (OU). Anisocoria was observed with the right pupil measuring 4 mm in the dark and 2 mm in the light and the larger left pupil measuring 6 mm in the dark with minimal constriction in the light. There was no relative afferent pupillary defect (RAPD). Magnetic resonance angiography (MRA) and digital subtraction angiogram (DSA) of the head showed a 7 mm left paraclinoid ICA aneurysm. Neurovascular neurosurgery placed a flow diverting stent into the left ICA. Repeat DSA demonstrated near-complete resolution of the left ICA ophthalmic segment aneurysm status post-flow diversion. At the last follow-up one year later, the patient was stable clinically and radiographically with no further recurrences. Clinicians should be aware that anisocoria can be a potentially life-threatening presentation of intracranial vascular lesions.