A 61-year-old man comes to the emergency department because of sudden-onset left-sided neck pain and headache. He has a history of hypertension and cigarette smoking. He takes lisinopril and hydrochlorothiazide. Physical examination shows left-sided ptosis and miosis. The left side of his face is dry compared with the right side. Extraocular movements are intact, and visual acuity is normal. CT angiography shows a dissection of the left internal carotid artery.
Disruption of which of the following pathways most directly explains this patient’s ocular and facial findings?
The correct answer is:
B) Postganglionic sympathetic fibers traveling along the internal carotid artery
This patient has Horner syndrome, characterized by ptosis, miosis, and anhidrosis due to disruption of sympathetic innervation to the head and neck. Postganglionic sympathetic fibers arise from the superior cervical ganglion and travel along the internal carotid artery to reach the eye and face. These fibers innervate the superior tarsal muscle, dilator pupillae, and facial sweat glands. Internal carotid artery dissection can injure these sympathetic fibers, producing ipsilateral ptosis, miosis, and facial anhidrosis with preserved extraocular movements.
Answer choice A: Parasympathetic fibers traveling with the oculomotor nerve, is incorrect. Parasympathetic fibers in cranial nerve III constrict the pupil through the sphincter pupillae and mediate accommodation through the ciliary muscle. A compressive oculomotor nerve lesion classically causes a dilated pupil, ptosis from levator palpebrae superioris weakness, and impaired extraocular movements, not miosis with intact eye movements.
Answer choice C: Preganglionic parasympathetic fibers traveling with the facial nerve, is incorrect. Preganglionic parasympathetic fibers of the facial nerve innervate the lacrimal, submandibular, and sublingual glands after synapsing in the pterygopalatine or submandibular ganglia. Injury to these fibers can impair lacrimation or salivation but does not cause Horner syndrome.
Answer choice D: Somatic motor fibers traveling with the abducens nerve, is incorrect. The abducens nerve innervates the lateral rectus muscle, which abducts the eye. Injury causes horizontal diplopia and impaired abduction of the affected eye, not ptosis, miosis, or anhidrosis.
Answer choice E: Somatic motor fibers traveling with the trochlear nerve, is incorrect. The trochlear nerve innervates the superior oblique muscle, which depresses and intorts the adducted eye. Injury causes vertical diplopia that worsens when looking down, such as while walking downstairs, but does not affect pupillary size or facial sweating.
Key Learning Point
Horner syndrome results from disruption of sympathetic fibers to the head and neck, which can occur when postganglionic fibers traveling along the internal carotid artery are injured.
