Friday, December 14, 2018

Horner Syndrome

Horner syndrome is a classic neurologic syndrome whose signs include miosis, ptosis, and anhidrosis.

NEUROANATOMY - Horner syndrome can result from a lesion anywhere along a three-neuron sympathetic pathway that originates in the hypothalamus:
●The first-order neuron descends caudally from the hypothalamus to the first synapse, which is located in the cervical spinal cord (levels C8-T2, also called ciliospinal center of Budge).

●The second-order neuron travels from the sympathetic trunk over the lung apex. It then ascends to the superior cervical ganglion, located near the bifurcation of the common carotid artery.

●The third-order neuron from superior cervical ganglia then ascends within the adventitia of the internal carotid artery, through the cavernous sinus. In the orbit and the eye, the oculosympathetic fibers innervate the iris dilator muscle as well as Müller's muscle, a small smooth muscle in the eyelids responsible for a minor portion of the upper lid elevation and lower lid retraction.
First-order syndrome - Lesions of the sympathetic tracts in the brainstem or cervicothoracic spinal cord can produce a first-order Horner syndrome.
The most common causes are:
(a)occlusion of PICA, which produces Horner syndrome as part of the Wallenberg syndrome.
(b)Brown-Séquard syndrome above T1, patient may present with ipsilateral Horner syndrome due to damage of oculosympathetic pathway.

Second-order syndrome — Second-order or preganglionic Horner syndromes can occur with trauma or surgery involving the spinal cord, thoracic outlet, or lung apex.Other causes include pancoast tumor involving the lung apex.

Third-order syndrome — Third-order Horner syndromes often indicate lesions of the internal carotid artery such as an arterial dissection, thrombosis, or cavernous sinus aneurysm

CLINICAL FEATURES -The classic signs of a Horner syndrome are ptosis, miosis, and anhidrosis.
1)The ptosis occurs as a result of paralysis of the Müller's muscle.
2)The degree of anisocoria is more marked in the dark than in light.
3)Anhidrosis is present in central or preganglionic (first- or second-order) lesions because the sympathetic fibers responsible for facial sweating branch off at the superior cervical ganglion along the external carotid artery and its branches.
4)Horner syndrome is also a common feature of cluster headache.

SOURCE-UpToDate, Kaplan.

-Srikar Sama.


  1. Beautiful explanation given by dr.srikar. i will show this article to my grandkids.

  2. Excellent. Each and every point very clear and scientific. Hope to receive more of such articles. Lot of hard work put in. Keep it up

  3. Excellent. Lot of hard work. Very very clear and scientific


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