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# Horner syndrome

Horner syndrome is a droopy eyelid, a small pupil and less sweating on one side of the face, caused by damage to the sympathetic nerves to the eye.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Sympathetic trunk](https://durgical.com/en/anatomy/sympathetic-trunk/)
- [Eyelids](https://durgical.com/en/anatomy/superior-tarsus/)
- [Internal carotid artery](https://durgical.com/en/anatomy/internal-carotid-artery/)
- [Iris](https://durgical.com/en/anatomy/iris/)
- [Levator palpebrae](https://durgical.com/en/anatomy/levator-palpebrae-superioris/)
- [Common carotid artery](https://durgical.com/en/anatomy/right-common-carotid-artery/)
- [Carotid sheath](https://durgical.com/en/anatomy/carotid-sheath/)
- [Brachial plexus roots](https://durgical.com/en/anatomy/roots-of-brachial-plexus/)
- [Hypothalamus](https://durgical.com/en/anatomy/hypothalamus/)
- [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/)

## Why it happens

- [Local effects of tumours and cancer cachexia](https://durgical.com/en/general-pathology/local-effects-of-tumours-and-cancer-cachexia/)
- [The autonomic nervous system: organization](https://durgical.com/en/physiology/the-autonomic-nervous-system-organization/)
- [The visual pathway, pupillary reflexes and eye movements](https://durgical.com/en/physiology/the-visual-pathway-pupillary-reflexes-and-eye-movements/)

## What it is

A clinical sign complex caused by interruption of the oculosympathetic pathway anywhere from the [hypothalamus](https://durgical.com/en/anatomy/hypothalamus/) to the eye, giving ipsilateral ptosis, miosis and, depending on the level, anhidrosis. It matters less for itself than for its cause, which can be a stroke, a carotid dissection or a tumour.

## Who gets it

Uncommon; it occurs at any age. Congenital cases are estimated at about 1 in 6,250 births. In adults, lung apex tumours, carotid dissection, brainstem stroke and neck or chest surgery and trauma are classic causes; in Colombia and Latin America, chest trauma, lung cancer in smokers and tuberculosis of the lung apex or neck nodes are part of the picture.

## Causes

- First-order (central) neuron: lateral medullary (Wallenberg) stroke, hypothalamic or brainstem lesions, cervical [spinal cord](https://durgical.com/en/anatomy/spinal-cord/) lesions above T1 (syringomyelia, trauma, demyelination)
- Second-order (preganglionic) neuron: apical lung tumour (Pancoast), neck or chest surgery, central line placement, birth trauma to the lower [brachial plexus](https://durgical.com/en/anatomy/roots-of-brachial-plexus/), neck masses
- Third-order (postganglionic) neuron: [internal carotid artery](https://durgical.com/en/anatomy/internal-carotid-artery/) dissection, [cavernous sinus](https://durgical.com/en/anatomy/cavernous-sinus/) lesions, cluster headache
- Children: birth trauma and neuroblastoma; congenital cases may show a lighter [iris](https://durgical.com/en/anatomy/iris/) on the affected side
- Some cases remain without an identified cause

## Risk factors

- Smoking (apical lung cancer)
- Neck trauma or chiropractic-type neck manipulation (carotid dissection)
- Vascular risk factors for brainstem stroke
- Neck, thyroid or chest surgery and central venous catheters
- Difficult delivery with traction on the arm (brachial plexus injury)

## Pathophysiology

Sympathetic fibres to the eye run in three neurons: from the hypothalamus down the brainstem to the cervicothoracic cord (C8–T2), then up the sympathetic chain to the superior cervical ganglion, then along the internal carotid artery to the dilator pupillae and the superior tarsal (Müller) muscle. Losing this tone weakens the dilator (miosis) and Müller muscle (mild ptosis); parasympathetic tone is left unopposed. Sweat fibres to the face leave with the external carotid, so anhidrosis is marked in central and preganglionic lesions and minimal or absent in postganglionic ones.

## Classification

- Central (first-order neuron)
- Preganglionic (second-order neuron)
- Postganglionic (third-order neuron)
- Congenital or acquired

## Symptoms and signs

- Mild drooping of the upper eyelid (ptosis), usually 1–2 mm, with slight elevation of the lower lid
- Small pupil on the affected side (miosis); the difference is greater in dim light
- Dilation lag: the small pupil dilates slowly when the light is turned off
- Reduced or absent sweating on the same side of the face (anhidrosis)
- Apparent sunken eye (pseudo-enophthalmos)
- In congenital cases, a lighter iris on the affected side (heterochromia)

## Red flags

- Acute Horner syndrome with neck, face or head pain (possible carotid dissection)
- Horner syndrome with vertigo, ataxia, dysphagia or crossed sensory loss (lateral medullary stroke)
- Shoulder or arm pain and hand weakness in a smoker (apical lung tumour)
- A child with acquired Horner syndrome or an abdominal or neck mass (neuroblastoma)
- New Horner syndrome with diplopia or other cranial nerve palsies (cavernous sinus lesion)

## Diagnosis

**Clinical**
Compare pupil size in bright and dim light, look for ptosis and anhidrosis, and search for associated signs that localise the lesion (brainstem signs, arm symptoms, neck pain). Ptosis with a small pupil points away from third nerve palsy, which gives a large pupil.

**Tests**
Pharmacological pupil testing confirms it: apraclonidine reverses the anisocoria (the Horner pupil dilates), or cocaine drops fail to dilate the affected pupil; hydroxyamphetamine can help separate postganglionic from earlier lesions. Urine catecholamine metabolites when neuroblastoma is suspected in a child.

**Imaging**
Imaging follows the pathway and urgency: urgent CT or MR angiography of the [head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) for acute painful Horner (dissection); brain MRI for central signs; [chest](https://durgical.com/en/anatomy/region/chest/) CT or X-ray of the lung apex for preganglionic lesions; neck, chest and abdominal imaging in children.

## Differential diagnosis

- Physiological (simple) anisocoria
- Third (oculomotor) nerve palsy, which has ptosis with a large pupil
- Adie tonic pupil
- Pharmacological miosis (opioids, pilocarpine)
- Aponeurotic (age-related) ptosis or myasthenia gravis

## Goal of treatment

Find and treat the underlying cause promptly, especially dangerous ones such as carotid dissection, stroke and tumours; the eye signs themselves usually need no treatment.

## Treatment

**Acute**
Acute painful Horner is handled as a possible carotid dissection or stroke, with urgent vascular imaging and stroke-pathway care.

**Medical**
Carotid dissection is usually treated with antiplatelet or anticoagulant drugs; other causes get their specific treatment (for example oncological treatment of an apical lung tumour or neuroblastoma).

**Surgical**
Surgery is directed at the cause (tumour resection); a cosmetic eyelid procedure is occasionally considered for persistent ptosis.

**Follow-up**
Follow-up of eye signs and of the underlying condition; in children, developmental and tumour surveillance as indicated.

## Complications

- Those of the cause: stroke from carotid dissection, spread of lung cancer or neuroblastoma
- Persistent cosmetic ptosis and anisocoria
- Iris heterochromia in congenital cases

## Prognosis

The eye signs are usually harmless and may persist; overall outcome depends entirely on the cause, from benign idiopathic cases to life-threatening dissection or cancer.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the classic triad of Horner syndrome?

Ipsilateral ptosis, miosis and anhidrosis, from loss of sympathetic supply to the eye and face.

## Which cause must be ruled out first in acute painful Horner syndrome?

Internal carotid artery dissection, with urgent CT or MR angiography of the head and neck.

## Which apical lung tumour classically causes Horner syndrome with shoulder pain?

A Pancoast (superior sulcus) tumour, which invades the sympathetic chain and lower brachial plexus.

## How does the pupil help separate Horner syndrome from third nerve palsy?

Horner gives ptosis with a small pupil; third nerve palsy gives ptosis with a large pupil and impaired eye movements.

## Which eye-drop test confirms Horner syndrome?

Apraclonidine reverses the anisocoria, or cocaine drops fail to dilate the affected pupil.

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## Related conditions

- [Lung cancer](https://durgical.com/en/conditions/lung-cancer/)
- [Ischaemic stroke](https://durgical.com/en/conditions/ischaemic-stroke/)
- [Cluster headache](https://durgical.com/en/conditions/cluster-headache/)
- [Neuroblastoma](https://durgical.com/en/conditions/neuroblastoma/)
- [Carotid artery stenosis](https://durgical.com/en/conditions/carotid-artery-stenosis/)
- [Thoracic outlet syndrome](https://durgical.com/en/conditions/thoracic-outlet-syndrome/)
- [Brainstem stroke syndromes (Wallenberg and others)](https://durgical.com/en/conditions/brainstem-stroke-syndromes/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Horner syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/horner-syndrome/) (MedlinePlus Genetics, US National Library of Medicine, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/conditions/horner-syndrome/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/horner-syndrome/