What is the best study to diagnose Horner's (Horner syndrome)?

Best Diagnostic Study for Horner's Syndrome

MRI is the recommended first-line imaging study for diagnosing Horner's syndrome, with specific protocols based on suspected lesion location. 1

Diagnostic Approach to Horner's Syndrome

Horner's syndrome results from interruption of the three-neuron oculosympathetic pathway and presents with the classic triad of ptosis, miosis, and facial anhidrosis. The diagnostic approach should focus on localizing the lesion and identifying the underlying cause.

Initial Pharmacological Testing

• Cocaine test: Confirms the diagnosis of Horner's syndrome
• 1% Phenylephrine test: Helps differentiate postganglionic from central/preganglionic lesions
• Apraclonidine test: Alternative to cocaine for confirming Horner's syndrome

Imaging Studies Based on Suspected Location

1. Central (First-Order Neuron) Lesions:

   • Brain MRI with contrast: Recommended for suspected central lesions (hypothalamus to upper thoracic spinal cord)
   • Look for stroke, demyelination, or tumors

2. Preganglionic (Second-Order Neuron) Lesions:

   • MRI of chest/thoracic inlet: For suspected Pancoast tumors or other thoracic pathology
   • CT chest: Alternative if MRI contraindicated

3. Postganglionic (Third-Order Neuron) Lesions:

   • MRA or CTA of the neck: First choice for suspected carotid artery dissection 1, 2
   • Particularly important with acute onset of occipital pain and Horner's syndrome

Targeted Imaging Based on Clinical Presentation

• Acute onset with pain: MRA or CTA of neck for suspected carotid artery dissection 1
• History of trauma: MRA or CTA of head and neck for suspected vascular injury
• Associated neurological deficits: Brain MRI for central lesions
• Suspected Pancoast tumor: MRI or CT of chest/thoracic inlet

Red Flags Requiring Urgent Imaging

• Associated neurological deficits (weakness, sensory loss)
• History of trauma
• Signs of vascular compromise
• Acute onset of occipital or neck pain (suggests carotid dissection)

Important Considerations

• Routine head CT is generally insufficient for diagnosing the cause of Horner's syndrome 2
• The American College of Radiology recommends MRI for suspected central or preganglionic lesions with high strength of evidence 1
• Imaging should be targeted based on clinical presentation and suspected location of the lesion
• In cases of suspected carotid artery dissection, prompt diagnosis using MRA or CTA of the neck is critical 1, 2

Pitfalls to Avoid

• Relying solely on clinical examination without confirmatory imaging
• Ordering non-targeted imaging studies that may miss the underlying pathology
• Delaying imaging in cases with red flags, particularly suspected vascular causes
• Using only head CT, which may not identify the underlying cause, especially for vascular or thoracic pathologies

Remember that the diagnostic approach should be guided by the suspected location of the lesion in the oculosympathetic pathway, with MRI being the preferred initial imaging modality for most cases of Horner's syndrome.