A patient undergoing left thoracoscopic sympathectomy at T2–T3 for palmar hyperhidrosis develops ipsilateral partial ptosis, miosis, and anhidrosis of the face. The most likely injured structure is:

• A Preganglionic sympathetic fibres to the superior cervical ganglion ✓
• B Phrenic nerve
• C Vagus nerve in the mediastinum
• D Recurrent laryngeal nerve

Explanation

Horner syndrome (ptosis, miosis, anhidrosis) results from interruption of the sympathetic pathway to the face. The preganglionic fibres originate from T1–T2 intermediolateral column, travel over the apex of the lung, and synapse in the superior cervical ganglion. T2–T3 sympathectomy risks damaging these preganglionic fibres as they ascend along the sympathetic chain, producing Horner syndrome. The phrenic and vagus nerves are not involved in this pathway.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.