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Internal and external carotid plexuses (oculosympathetic pathway)

Postganglionic · α1 Third-order neurone

Postganglionic fibres from the superior cervical ganglion climb the internal carotid artery through the cavernous sinus, join V1 and reach the eye in the long ciliary (nasociliary) nerves and via the ophthalmic artery to the superior tarsal muscle. Sudomotor and vasomotor fibres for the face instead follow the external carotid artery.

Traced from the start

  1. Sympathetic (thoracolumbar) outflow
  2. Intermediolateral cell column T1–L2 via white rami communicantes
  3. Superior cervical ganglion
  4. Internal and external carotid plexuses (oculosympathetic pathway)

Detail

Eye route
Internal carotid nerve → plexus in cavernous sinus → ophthalmic nerve → nasociliary → long ciliary nerves → dilator pupillae; some fibres traverse the ciliary ganglion in short ciliary nerves
Lid route
With the ophthalmic artery and CN III branches to the superior tarsal (Müller) muscle — provides 1–2 mm of lid elevation
Face route
External carotid plexus → facial and superficial temporal arteries → sweat glands and vessels of the face
Pharmacological tests
Apraclonidine 0.5–1% reverses the anisocoria (denervation supersensitivity of α1) — confirms Horner; cocaine 4–10% fails to dilate any Horner pupil; hydroxyamphetamine 1% dilates a preganglionic but not a postganglionic Horner pupil

When it goes wrong

Lesion of the third-order neurone: internal carotid dissection, cavernous sinus thrombosis or tumour, skull base fracture

Horner syndrome with sweating of the face preserved (or lost only on the forehead), often with ipsilateral pain; the hydroxyamphetamine test fails to dilate the pupil

Cavernous sinus lesion involving the plexus together with CN VI

Horner syndrome with an ipsilateral abducens palsy — a classic localising pair

Practise this structure

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