A Case of Horner's Syndrome Aiding the Diagnosis of Internal Carotid Artery Dissection (ICAD): A Life-Saving Twist of Fate.

A 59-year-old male patient came to the outpatient department with complaints of left-sided hemicranial headache with drooping of the left upper eyelid (UL) for three days associated with difficulty in swallowing and deviation of the tongue. The patient had a history of vigorous coughing for the past 15 days for which he did not take any medications. He was thoroughly evaluated in the outpatient department and diagnosed with Horner's syndrome. Acute Horner's syndrome with pain is nearly a hallmark of carotid dissection, and MRI of the brain and orbit was thus advised. On MRI, a hyperdense area was noted around the left internal carotid artery for which he was advised magnetic resonance angiography, which revealed internal carotid artery dissection (ICAD) of the left side. The patient was diagnosed with left-sided Horner's syndrome following left ICAD with involvement of the left hypoglossal nerve. He was started on antiplatelets and anticoagulants and closely followed up. Early diagnosis and prompt treatment were lifesaving for this patient.