Horner's syndrome (miosis, ptosis, anhidrosis) results from interruption of the sympathetic chain. The finding of anhidrosis is limited to the face when the lesion is at which level?

• A Central (hypothalamus or brainstem) — above the cilio-spinal centre of Budge
• B Preganglionic (C8-T1 and T2 spinal cord or superior cervical ganglion level)
• C Postganglionic fibres traveling with the external carotid artery ✓
• D Postganglionic fibres along the internal carotid artery (cavernous sinus lesion)

Explanation

Facial sweating fibres diverge from the ocular sympathetic chain at the superior cervical ganglion. Fibres to the face travel along the external carotid artery branches to reach sweat glands. Postganglionic fibres to the eye (dilator pupillae and superior tarsal muscle) travel with the internal carotid artery. A lesion of postganglionic fibres along the external carotid branch selectively causes anhidrosis of the face, while preserving the pupillomotor and lid fibres. Internal carotid postganglionic lesions (e.g., cavernous sinus) spare facial sweating because they only affect ocular fibres.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.