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Review
. 2019 Jan;60(1):81-88.

A review of Horner's syndrome in small animals

Danielle M Zwueste  1 , Bruce H Grahn  1
Affiliations
Review

A review of Horner's syndrome in small animals

Danielle M Zwueste et al. Can Vet J. 2019 Jan.

Erratum in

  • Erratum.
    [No authors listed] [No authors listed] Can Vet J. 2023 Nov;64(11):1050. Can Vet J. 2023. PMID: 37915785 Free PMC article.

Abstract
in English, French

Horner's syndrome arises from dysfunction of the oculosympathetic pathway and is characterized by miosis, enophthalmos, protrusion of the third eyelid, and ptosis. It has been recognized in a wide variety of breeds and ages in small animal patients. The oculosympathetic pathway is a 3-neuron pathway. The central/first order neuron arises from the hypothalamus and extends down the spinal cord. The preganglionic/second order neuron arises from the first 3 thoracic spinal cord segments and travels through the thorax and cervical region until it synapses at the cranial cervical ganglion. The postganglionic/third order neuron travels from this ganglion to the orbit. Topical application of cocaine is the gold standard for differentiating Horner's syndrome from other causes of miosis. Topical 1% phenylephrine allows for identification of a post-ganglion Horner's syndrome. Numerous etiologies have been reported for Horner's syndrome, but idiopathic disease is most common. Ancillary diagnostics include otoscopic examination, thoracic radiographs, or advanced imaging. Treatment and prognosis are determined by the etiology.

Examen du syndrome de Horner chez les petits animaux. Le syndrome de Horner provient d’une dysfonction de la voie oculo-sympathique et est caractérisée par la miose, l’enophtalmie, la protrusion de la troisième paupière et la ptose. Elle a été reconnue chez une grande variété de races et d’âges chez les patients petits animaux. La voie oculo-sympathique est une voie à trois neurones. Le neurone central/de premier ordre provient de l’hypothalamus et s’étend vers le bas sur la colonne vertébrale. Le neurone préganglionnaire/de deuxième ordre provient des trois premiers segments thoraciques de la colonne vertébrale et se déplace dans le thorax et la région cervicale jusqu’à la synapse au ganglion cervical crânien. Le neurone postganglionnaire/de troisième ordre se déplace de ce ganglion jusqu’à l’orbite. L’application topique de cocaïne est le test de référence pour la différenciation du syndrome de Horner des autres causes de miose. La phényléphrine topique 1 % permet l’identification d’un syndrome de Horner postganglionnaire. Plusieurs étiologies ont été signalées pour le syndrome de Horner, mais la maladie idiopathique est la plus commune. Les diagnostics auxiliaires incluent l’examen otoscopique, des radiographies thoraciques ou une imagerie avancée. Le traitement et le pronostic sont déterminés par l’étiologie.(Traduit par Isabelle Vallières).

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Figures

Figure 1
Figure 1
Clinical manifestation of unilateral Horner’s syndrome in the right eye of a cat. Note the miosis, enophthalmos, and prolapsed third eyelid. Ptosis was also present, but the eyelids are being retracted in the photo to emphasize the anisocoria.
Figure 2
Figure 2
Schematic representation of the oculosympathetic pathway superimposed over a sagittal cervical and thoracic CT image. The central/first order neuron begins within the hypothalamus and travels through the lateral tectotegmental spinal tract (1). The preganglionic/second order neuron begins within the gray matter of the first 3 thoracic spinal cord segments (T1, T2, T3). Its axon continues through the ramus communicans and travels though the thorax within the sympathetic trunk (2a). It will pass through but not synapse within the cervicothoracic ganglion (A) and middle cervical ganglion (B). The sympathetic trunk fuses with the vagus nerve and travels through the cervical region as the vagosympathetic trunk (2b), ultimately synapsing in the cranial cervical ganglion (C). The post-ganglionic axon will then enter the calvarium and continue to the orbit.
Figure 3
Figure 3
Cross section of the first 3 thoracic spinal cord segments. The central/first order axon travels from the brain through the spinal cord via the lateral tectotegmentospinal tract, located within the lateral funiculus of the white matter (A). It will synapse with the preganglionic/second order cell body (B) within the intermediolateral horn of the gray matter (C). The preganglionic axon exits the spinal cord via the ventral nerve root (D), travels a short distance within the spinal nerve (E) and then separates as the ramus communicans (F).
Figure 4
Figure 4
One proposed pathway of the third order/post-ganglionic neuron, shown travelling through the calvarium from a dorsal (A) and oblique (B) perspective. After passing through the tympanic bulla, the nerve enters the calvarium and travels ventral to the trigeminal nerve within the trigeminal canal (asterisk). It exits the calvarium via the orbital fissure (arrow) and enters the orbit
See this image and copyright information in PMC

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