Early Neuroimaging Identifies ICA Dissection in Acute Horner’s Syndrome

The high rate of incidental findings in Horner’s syndrome patients and distinguishing between acute, subacute and chronic presentations underscore the need for careful interpretation to optimize resource use. Photo: Jessica Steen, OD, and Joseph Sowka, OD. Click image to enlarge. Detecting Horner’s syndrome quickly is crucial before it becomes life-threatening to the patient, with neuroimaging being a key component, as it helps detect structural causes such as vascular, neoplastic, traumatic or inflammatory processes. Researchers of a recent study sought to determine the prevalence of structural causes in Horner’s and assess the clinical significance of incidental neuroimaging findings. They found that structural causes of this condition are more frequently identified in acute and subacute presentations, with internal carotid artery (ICA) dissection the leading cause in acute cases—supporting the need for early imaging.A total of 134 patients with pharmacologically confirmed Horner’s syndrome who underwent neuroimaging at a tertiary neuro-ophthalmology clinic between 2018 and 2024 were included. Neuroimaging findings were reviewed and categorized as either structural causes of Horner’s or incidental. The latter findings were further classified based on their clinical relevance and need for follow-up. Cases were stratified by symptom duration into acute (less than 21 days), subacute (21 days to three months) and chronic (more than three months). For advice on how to manage Horner’s syndrome patients, see this feature.  A structural cause for Horner’s syndrome was identified in 14.9% (20) of patients, with higher detection rates in acute (26%) and subacute (21.4%) presentations compared to chronic cases (6.5%)—which is often benign or idiopathic. This aligns with previous studies that highlighted acute Horner’s frequently arises from vascular abnormalities, such as ICA dissection. “In our study, ICA dissection was the leading cause in acute cases (3% overall, 2.2% in acute Horner syndrome), underscoring the importance of urgent neuroimaging—CT/CTA or MRI/MRA—in this group,” the authors wrote in their paper for Canadian Journal of Ophthalmology. “Subacute cases revealed additional important findings, including bilateral ICA dissection and brachial plexus infiltration.”The lower imaging yield in chronic Horner’s syndrome suggests that neuroimaging may be deemphasized unless new symptoms or changes in clinical context emerge, the authors noted. “Most chronic cases reflect benign causes, such as postsurgical damage to the sympathetic pathway and idiopathic etiologies.”Incidental findings were observed in 35.6% (47) of patients with most benign and most commonly microangiopathic changes (10%), sinus/mucosal changes (3%) and thyroid nodules (3%). While 18.2% of patients required routine follow-up, two cases required urgent follow-ups and none required emergency intervention. The authors noted that this underscores the growing challenge of modern imaging modalities, where increased sensitivity often reveals unrelated abnormalities.In conclusion, the key findings of this study are the following:In acute Horner’s, urgent imaging is essential to identify critical causes, such as ICA dissection.In subacute cases, targeted imaging remains necessary for detecting structural pathology.In chronic presentations, imaging should be guided by clinical context to avoid over usage.“By distinguishing between acute, subacute and chronic presentations and implementing a systematic approach to incidental findings, clinicians can optimize diagnostic accuracy, improve resource utilization and enhance patient care.”Click here for the journal source. Jafari S, Margolin E, Micieli MA. Causes and incidental neuroimaging findings in pharmacologically confirmed Horner syndrome: a retrospective cohort study of 134 cases. Can J Ophthalmol. September 11, 2025. [Epub ahead of print.] This article was developed by the editorial staff in conjunction with experts in the field. In the process, AI may have been among the editorial tools used to meet the goals of human editors, who approved all content.