Each case was classified based on:

• Clinical Presentation: Ptosis, miosis, and anhidrosis.
  

  Fig 2: Triad of symptoms in Horner's syndrome: ptosis, miosis, and anhidrosis. Graphic representation of a patient presenting these three symptoms
• Lesion Localization: Central (hypothalamus/brainstem), Preganglionic (cervical/thoracic), or Postganglionic (carotid plexus to orbit).
  

  Fig 1: Graphic representation of Horner's syndrome, based on key anatomical elements. Inspired by Radiology Assistant, graphic created by the author. The central pathway is marked in purple, the preganglionic part in blue, and the postganglionic part in green.
• Etiology Categorization: 
  

  Fig 3: Main etiologies of Horner's syndrome, grouped by location
• Imaging Efficacy: Evaluated through diagnostic yield, lesion localization accuracy, and impact on patient management.

Lesion Distribution & Imaging Correlation

Central Lesions (First-Order Neuron)

Fig 4: Central causes, anatomical landmarks

• Common causes: Brainstem infarcts (e.g., lateral medullary syndrome), demyelination, neoplasms.
  

  Fig 5: The most common causes of central involvement in Horner's syndrome.
• Examples:
• Ischemic Stroke: A 56-year-old male with cardiovascular risk factors presented with left Horner’s syndrome, vertigo, and occipital headache. Initial CT was negative; MRI confirmed a left medullary infarct, consistent with Wallenberg syndrome.
  

  Fig 6: On the left: Graphic representation of the central portion of the sympathetic chain (purple), highlighting the level where the chain is interrupted (red). On the right: Wallenberg syndrome; axial images DWI (A), ADC (B), FLAIR (c) and T2-WI (D) illustrating restricted diffusion the left medulla, matching FLAIR and T2 hyper signal. Department of Radiology, Clinical Emergency Hospital "Prof. Dr. N. Oblu" Iasi
• Multiple Sclerosis: A 21-year-old presented with right-sided Horner’s syndrome and paresthesia. MRI showed periventricular lesions with “Dawson’s fingers” and an active demyelinating lesion. Lumbar puncture confirmed multiple sclerosis.
  

  Fig 7: On the left: Graphic representation of the central portion of the sympathetic chain (purple), highlighting the level where the chain is interrupted (red). On the right: Multiple Sclerosis; MRI images (A-D) illustrate demyelinating lesions affecting central pathways. Notable findings include Dawson’s fingers (B), and an enhancing lesion with an open ring sign (C), spinal cord imaging reveals two small T2-hyperintense lesions: one at the C5-C6 intervertebral space and another at the C1-C2 level, fulfilling both spatial and temporal dissemination criteria. Department of Radiology, Clinical Emergency Hospital "Prof. Dr. N. Oblu" Iasi
• Chiari I Malformation: A 23-year-old female with Chiari I and syringomyelia developed left-sided Horner’s syndrome. MRI showed syringomyelia from C2 to D1.
  

  Fig 8: On the left: Graphic representation of the central portion of the sympathetic chain (purple), highlighting the level where the chain is interrupted (red). On the right: Chiari I Malformation; MRI images (A-C) reveal the presence of syringomyelia extending from C2 to D1, with a maximum diameter of approximately 15 mm at the C2-C3 level. Department of Radiology, Clinical Emergency Hospital "Prof. Dr. N. Oblu" Iasi

Preganglionic Lesions (Second-Order Neuron)

Fig 9: Preganglionic causes, anatomical landmarks

• Common causes: Pancoast tumors, spinal cord trauma, cervical spine pathologies.
  

  Fig 10: The most common causes of preganglionic involvement in Horner's syndrome.
• Examples:
• Pancoast Tumor: A 55-year-old male with right shoulder pain and ptosis was diagnosed via chest radiograph. (Case courtesy of Craig Hacking, Radiopaedia.org, rID: 73294.)
  

  Fig 11: On the left: Graphic representation of the preganglionic portion of the sympathetic chain (blue), highlighting the level where the chain is interrupted (red). On the right: an anteroposterior chest radiograph confirmed a right apical tumor. (Case courtesy of Craig Hacking, Radiopaedia.org, rID: 73294.)
• Ganglioneuroblastoma: A 2-year-old male presented with chest discomfort. Imaging showed a 5.0x2.7 cm posterior mediastinal mass. Postoperative recovery was uneventful except for persistent left Horner’s syndrome. (Case courtesy of Ryan Thibodeau, Radiopaedia.org, rID: 161772.)
  

  Fig 12: On the left: Graphic representation of the preganglionic portion of the sympathetic chain (blue), highlighting the level where the chain is interrupted (red). On the right: Ganglioneuroblastoma; imaging findings (A-F) include chest X-rays (A, B) and CT scans with lung and mediastinal windows (C-F), revealing a well-circumscribed soft tissue mass in the left posterior mediastinum (5.0 x 2.7 cm), extending from T1 to T5. The lesion abuts the proximal descending aorta and the left subclavian artery without mass effect or vascular encasement. There is close approximation to the neural foramen (T2-T5) but no definite spinal canal invasion. (not shown here). Case courtesy of Ryan Thibodeau, Radiopaedia.org, rID: 161772
• Neoplastic Brachial Plexopathy: A 47-year-old female with previous breast cancer developed left Horner’s syndrome. Imaging confirmed neoplastic involvement. (Case courtesy of Dalia Ibrahim, Radiopaedia.org, rID: 27819.)
  

  Fig 13: On the left: Graphic representation of the preganglionic portion of the sympathetic chain (blue), highlighting the level where the chain is interrupted (red). On the right: Neoplastic brachial plexopathy; MRI images (A-C) reveal an irregularly shaped, spiculated soft tissue mass in the left supraclavicular region invading the left brachial plexus (red arrows). The lesion appears hyperintense on T2/STIR sequences, with mild post-contrast enhancement (not shown), likely representing a metastatic mass. Additionally, multiple enlarged bilateral deep cervical, right supraclavicular, right axillary, and superior mediastinal lymph nodes (orange arrows) suggest metastatic involvement. Case courtesy of Dalia Ibrahim, Radiopaedia.org, rID: 27819

Postganglionic Lesions (Third-Order Neuron)

Fig 9: Preganglionic causes, anatomical landmarks

• Common causes: carotid artery dissection (CAD), skull base lesions, or cavernous sinus involvement.
• Examples:
• Carotid Artery Dissection: A 53-year-old male presented with right-sided Horner’s syndrome and neck pain. Imaging showed atheromatous plaque with 80% luminal stenosis.
  

  Fig 16: On the left: Graphic representation of the postganglionic portion of the sympathetic chain (green), highlighting the level where the chain is interrupted (red). On the right: Carotid Artery Dissection; CT angiography images (A, B) reveal atherosclerotic plaque with dissection/ulceration at the level of the right internal carotid artery (ICA) bulb, leading to approximately 80% luminal stenosis. Department of Radiology, Clinical Emergency Hospital "Prof. Dr. N. Oblu" Iasi
• Carotid Artery Dissection: A 55-year-old male with acute left-sided Horner’s syndrome had CTA confirming ICA dissection with a mural thrombus. MRI revealed the "crescent sign."
  

  Fig 17: On the left: Graphic representation of the postganglionic portion of the sympathetic chain (green), highlighting the level where the chain is interrupted (red) with the "croissant sign" site highlighted (green box). On the right: Carotid Artery Dissection; multimodal imaging findings (A-D) from a case of acute left internal carotid artery (ICA) dissection. CT imaging (A, B) shows a narrowed lumen of the left ICA with a crescent-shaped hyperattenuating focus, suggestive of a mural thrombus extending towards the skull base. MRI (C, D) reveals the characteristic 'crescent sign' with high T1 and T2 signal surrounding the ICA, corresponding to the hyperdensity seen on non-contrast CT. Case courtesy of Andrew Dixon, Radiopaedia.org, rID: 53541
• Schwannoma: A 16-year-old female presented with a painless neck mass. MRI showed an enhancing oval mass in the upper cervical region, displacing adjacent structures. (Case courtesy of Mohammad Taghi Niknejad, Radiopaedia.org, rID: 25154.)
  

  Fig 18: On the left: Graphic representation of the postganglionic portion of the sympathetic chain (green), highlighting the level where the chain is interrupted (red). On the right: Schwannoma; contrast-enhanced CT images (A, B) demonstrate a well-defined, oval-shaped, enhancing mass in the right upper cervical region. The lesion is located between the sternocleidomastoid muscle and the main cervical vessels, displacing the internal jugular vein and the common carotid artery medially without signs of local invasion. A small calcification is present within the mass. Case courtesy of Mohammad Taghi Niknejad, Radiopaedia.org, rID: 25154
• Carotid Paraganglioma: A 65-year-old female with left brachial monoparesis had MRI findings suggestive of a carotid paraganglioma. Angio-CT later confirmed the diagnosis.
  

  Fig 19: On the left: Graphic representation of the postganglionic portion of the sympathetic chain (green), highlighting the level where the chain is interrupted (red). On the right: Carotid Paraganglioma; On the right, MRI sequences (A-E) demonstrate a well-defined, expansile lesion located in the left carotid space, above the common carotid artery bifurcation. The mass measures approximately 25×25×43 mm (AP/T/CC) and exhibits heterogeneous T1 (A), T2(B, D and E), and STIR (C) signal intensity (predominantly hyperintense) with heterogeneous contrast enhancement (not shown here). The lesion displaces and separates the internal and external carotid arteries, extends superiorly to the jugular bulb without evident bony changes, and encases/compresses the left internal jugular vein. The imaging features are highly suggestive of a carotid body paraganglioma, warranting further CT angiography of the supra-aortic trunks for confirmation (not shown here). Department of Radiology, Clinical Emergency Hospital "Prof. Dr. N. Oblu" Iasi
• Carotid-Cavernous Fistula: A 75-year-old female with right-sided Horner’s syndrome, chemosis, and pulsatile tinnitus had Angio-CT findings consistent with a bilateral indirect carotid-cavernous fistula (Type D).
  

  Fig 20: On the left: Graphic representation of the postganglionic portion of the sympathetic chain (green), highlighting the level where the chain is interrupted (red). On the right: Carotid-Cavernous Fistula; Angio-CT images (A-D) demonstrate findings consistent with a bilateral indirect carotid-cavernous fistula (Type D). The images reveal abnormal vascular connections at the level of the cavernous sinus with arterialization of the venous structures, which may lead to ocular and orbital venous congestion, cranial nerve dysfunction, and postganglionic Horner’s syndrome. Department of Radiology, Clinical Emergency Hospital "Prof. Dr. N. Oblu" Iasi
• Pituitary Macroadenoma: A 56-year-old male developed right-sided Horner’s syndrome postoperatively due to tumor hemorrhage and brainstem compression. This case could be included in the "Central Horner type" also.
  

  Fig 21: On the left: Graphic representation of the postganglionic portion of the sympathetic chain (green), highlighting the level where the chain is interrupted (red). On the right: Pituitary Macroadenoma - Apoplexy; multimodal imaging findings (A-G) demonstrate a large sellar, infra-, supra-, and laterosellar solid mass (54×46×75 mm), consistent with a macroadenoma. The lesion exhibits mild hypointensity on T1 (B), slight hyperintensity on T2 (C and E) and moderate homogeneous contrast enhancement (D and F). The pituitary stalk is not visualized. Postoperative CT scan (G) shows: hemorrhagic densities within the macro adenoma, suggestive of pituitary apoplexy. Additional findings include bilateral frontal pneumocephalus, triventricular active internal hydrocephalus, and minimal declivous hemorrhagic effusion in the occipital horns of the lateral ventricles (not shown here). Department of Radiology, Clinical Emergency Hospital "Prof. Dr. N. Oblu" Iasi

Diagnostic Efficiency of Imaging Protocols

• MRI/CT Improved Detection Rates: Enhanced lesion identification, particularly in brainstem and vascular pathologies.
• Reduced Unnecessary Investigations: Targeted imaging minimized redundant tests.
• Shortened Time to Diagnosis: Rapid interpretation facilitated early intervention in vascular emergencies.
• Graphic Illustrations: Color-coded images clarified lesion localizations along the sympathetic pathway.