Traumatic Horner Syndrome
Horner syndrome, known classically by its presenting triad of miosis (pupillary constriction), eyelid ptosis (drooping), and facial anhidrosis (decreased sweating), results from damage to the sympathetic pathways between the hypothalamus and ocular adnexa.  In clinical practice, however, definitive diagnosis can be challenging as patients rarely present with the complete triad of signs and symptoms. Figure 1 demonstrates the classic appearance of a left-sided Horner syndrome with apparent pupillary miosis and ipsilateral eyelid ptosis.
Although Horner syndrome can result from a variety of mechanisms (Table 1), the most common etiologies are neoplastic (35-60% of all cases). Other less common causes include iatrogenic injury (10-18.5%) and trauma (4-13% inclusive of birth-related injuries). This article specifically focuses on the diagnosis and management of Traumatic Horner syndrome.
Horner syndrome is caused by a lesion to the first, second, and/or third order neurons that comprise the sympathetic pathways that innervate the head and neck. The long anatomical pathway of the oculosympathetic chain makes it particularly vulnerable to many pathological processes and injury. Pupil size is mediated by autonomic control of iris constriction and dilation, and is based upon both endogenous and exogenous mediators along with physiological stimuli. Pupillary constriction is controlled by parasympathetic fibers originating in the ciliary ganglia that innervate the pupillary constrictor muscle. In contrast, pupillary dilation is mediated by sympathetic fibers originating from the superior cervical ganglion that innervate the pupillary dilator muscle. Damage to the sympathetic pathway thereby limits the ability for the pupil to dilate, and results in ipsilateral miosis secondary to unopposed pupillary constriction by the intact parasympathetic system. The following section summarizes the impact of common mechanisms of trauma at various anatomic locations along the oculosympathetic chain (Figure 2):
First-Order (Central) Neuron: Hypothalamus → Ciliospinal Center of Bulge (C8-T2)
- Vertebral artery dissection: Motor vehicle accident (MVA), blunt neck trauma, strangulation, chiropractic manipulation, sudden neck movements, severe coughing
- Cervical cord trauma (MVA, falls, penetrating or blunt trauma, sport-related or diving injuries)
- Post-traumatic late-stage Syringomyelia (if above T1)
- Brown-Séquard syndrome (if above T1)
Second-Order (Preganglionic) Neuron: Ciliospinal Center of Bulge (C8-T2) → Superior Cervical Ganglion
- Penetrating neck trauma (stab wounds, gunshot wounds)
- Trauma to brachial plexus/soft tissue of neck
- Fracture of the first rib 
- Pneumothorax 
- Neck Hematoma 
- Birth trauma 
Third-Order (Postganglionic) Neuron: Superior Cervical Ganglion → Pupillary Dilator Muscles of Iris and Smooth Muscle of Upper and Lower Eyelid (Muller’s muscle)
- Carotid Artery Dissection
- Damage to superior cervical ganglion (due to penetrating intraoral injury)
Birth trauma (complex vaginal delivery, forceps, etc.) may result in Horner syndrome, most commonly at the level of the second-order neuron, and can be associated with concomitant brachial plexus injury.
Pupil examination: Anisocoria
Given the broad differential diagnosis associated with head and neck trauma, it is critical to rule out potentially life threatening diagnoses that can be associated with pupil asymmetry (anisocoria) and ptosis. A prompt and comprehensive neuro-ophthalmic examination is critical to differentiate if the larger pupil is too dilated (mydriatic), or if the smaller pupil is too constricted (miotic). Optimizing ambient lighting conditions and using a bright light source in both dim and illuminated settings will help make this critical differentiation.
If the anisocoria is greater in bright illumination, then the eye with the larger pupil is the affected eye. In this case, a contralateral Horner Syndrome can be ruled out, and attention directed to disorders of the parasympathetic system (Adie tonic pupil, postsurgical mydriasis, secondary glaucoma, pupillary synechiae, oculomotor nerve palsy, pharmacological/narcotic contaminants etc.) (Table 2) in the mydriatic eye.
If the anisocoria is greater in dim illumination, then the eye with the miotic pupil is likely abnormal, and an ipsilateral Horner syndrome remains a possibility. It is important to note that mild (up to 1mm) physiological (essential) anisocoria is present in up to 15-30% of the normal population, and is not associated with any central nervous system pathology. This physiological type of anisocoria is characterized by a stable difference in size in both bright and dim ambient lighting.
Small pupils in settings of anisocoria may also be secondary to uveitis, eye trauma, diabetic eye disease, topical eye drops or ocular surface contaminants (pilocarpine, narcotics, parasympathomimetics), postoperative changes, etc.
Eyelid Evaluation: Ptosis
The presence of concomitant ptosis with pupillary miosis should place Horner syndrome higher on the differential, particularly if accompanied by anhidrosis. Ptosis, however, can occur for a variety of reasons, and similar to the pupil examination, clinical examination should focus on whether the asymmetry in lid position is truly due to ipsilateral ptosis, or on the other hand, contralateral eyelid retraction. For example, if manual elevation of the ptotic lid results in lowering of the contralateral eyelid (Positive Hering’s Test), this is indicative of ipsilateral ptosis with compensatory lifting. Hertel exophthalmometry should also be performed to rule out lid changes secondary to proptosis of the contralateral eye.
Although traumatic Horner's syndrome is fairly rare, it is particularly important to consider this diagnosis in the setting of head, neck, and chest injury. As there is great variability in presentation, and often a paucity of associated symptoms, significant diagnostic challenges exist. Of note, a study of 146 patients with cervical internal carotid artery dissection, Horner syndrome was the initial and sole manifestation in half of these cases. Obviously, early identification of this severe and life-threatening condition in collaboration with vascular surgery may provide a potentially life-saving intervention.
In the setting of trauma, a thorough history obtained from all available sources (patient, family, witnesses, first responders, etc.) focused on the mechanism of action, along with any relevant neurological and ophthalmic history, is critical to guide further workup, radiological studies, and consultation. It is important to note that a chronic Horner syndrome may be incidentally discovered following trauma, as well as the possibility that the patient may have other causes of anisocoria and/or miosis (Table 2). A targeted neuro-ophthalmic examination with pharmacological testing once signs of Horner syndrome are localized can help identify the level of the pathology. Of note, close coordination with the emergency department, nursing, and any consulting doctors (neurology, neurosurgery, etc.), particularly before performing pharmacological testing, is essential to avoid medical errors. For more detailed information on clinical examination and pharmacological tests, visit: https://eyewiki.org/Horner_Syndrome#Examination
Pediatric patients with suspected Horner syndrome should be evaluated with a thorough history, and if clinically safe to do so, physical examination including palpation of the neck, abdomen, and axilla with close follow-up and frequent neurologic checks if indicated. Though Horner syndrome in the pediatric population is rare (incidence of 1.42 per 100,000 patients), there should be suspicion of Horner syndrome in cases of birth trauma or complicated deliveries, especially with one or more presenting symptoms from the classic triad. Birth trauma resulting in brachial plexus injury is the most common cause of congenital Horner’s syndrome, and other rare causes include thoracic and cervical neuroblastoma, internal carotid artery agenesis, carotid artery aneurysm, and complications from perinatal surgical procedures .
Acute onset of Horner syndrome following trauma should be evaluated immediately to further prevent trauma-associated injury. It should be considered a neurological emergency and managed accordingly. For more insidious onset Horner syndrome following trauma, the underlying cause should be identified and treated. Horner syndrome does not generally result in major functional deficits, and patients are usually fairly asymptomatic with the exception of concerns regarding facial asymmetry and cosmesis. Temporary correction of the eyelid position can be achieved with the use of topical medications or hyaluronic acid gel injections. Surgical ptosis repair can provide a more permanent restoration of facial and eyelid symmetry.
Horner syndrome results from disruption of the oculosympathetic pathways, and is associated with ptosis, miosis, and anhidrosis, although patients rarely present with this complete triad. Although there are many causes of Horner syndrome, head, neck, and chest trauma can each precipitate the syndrome. Of note, carotid artery dissection, particularly in the setting of trauma, should be considered an emergency. Careful neuro-ophthalmic evaluation can help differentiate Horner Syndrome from other disease entities that impact pupil and eyelid anatomy and physiology. Once a diagnosis has been made, treatment is targeted to the underlying condition, and may include cosmetic treatments to improve lid and facial asymmetry.
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