Acute Horner Syndrome and Warning Signs of Carotid Artery Dissection

Acute Horner syndrome is an important neuro-ophthalmic warning sign because subtle unilateral ptosis and miosis may precede retinal or cerebral ischemia from internal carotid artery dissection. The classic combination of ptosis, miosis, and anhidrosis is often incomplete, and preserved visual acuity or absence of weakness does not establish a benign cause. This narrative review examines clinical recognition, anatomical localization, warning symptoms, pharmacological testing, imaging selection, and the implications of a confirmed dissection. Targeted PubMed searches and contemporary professional guidance were used to identify clinical cohorts, diagnostic studies, imaging comparisons, randomized trials, and relevant recommendations. Numerical findings were interpreted descriptively without generating a new pooled estimate. Ipsilateral orbital, facial, head, or neck pain, transient monocular visual loss, pulsatile tinnitus, neurological deficits, and recent cervical trauma or mechanical strain increase concern, although dissection can occur without a recognized trigger or prominent pain. Apraclonidine can support the diagnosis but may be falsely negative early and should not delay vascular imaging when suspicion is substantial. Computed tomography angiography of the head and neck is particularly appropriate for acute painful or traumatic presentations, while magnetic resonance imaging adds information about ischemia, mural hematoma, and alternative central lesions when clinically indicated. A normal noncontrast head scan or carotid ultrasound does not adequately exclude the relevant vascular pathology. Confirmed dissection warrants prompt stroke-specialist assessment, individualized antithrombotic treatment, and evaluation for acute reperfusion therapy when ischemic stroke is present. Recognition depends on integrating pupil and eyelid findings with symptom chronology, and safety depends on investigating the cause rather than treating pharmacological confirmation as a prerequisite for urgent assessment.