Horner's syndrome (ptosis, miosis, anhidrosis, and enophthalmos) results from interruption of sympathetic pathways to the head and eye. At which level of the three-neuron sympathetic chain would a lesion cause anhidrosis of the ipsilateral ENTIRE face and neck but spare the upper extremity?

• A First-order neuron (hypothalamus to ciliospinal center of Budge at C8-T2)
• B Third-order neuron (superior cervical ganglion to eye via the internal carotid artery plexus)
• C Second-order neuron (C8-T2 to superior cervical ganglion, passing over the lung apex) ✓
• D Third-order neuron injury always spares facial sweating since sweat fibers travel separately

Explanation

The second-order (preganglionic) neuron travels from the ciliospinal center (C8-T2) over the lung apex, through the stellate ganglion, and synapses in the superior cervical ganglion. Lesions here (e.g., Pancoast tumor at lung apex) interrupt sweat fibers to the entire ipsilateral face, neck, and upper limb. First-order lesions (hypothalamus) also cause anhidrosis of the entire ipsilateral body. Third-order (postganglionic) lesions cause anhidrosis only of the medial forehead and nose (fibers traveling with the internal carotid) since sweat fibers to the face diverge earlier via the external carotid.

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

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Written and medically reviewed by the StethoPrep medical team.