A patient presents with Horner's syndrome and absence of sweating on one side of the face. Which of the following structures is most likely compressed?

1. A

   Sympathetic chain

2. B

   Internal carotid plexus

3. C

   Vagus nerve

4. D

   Common carotid artery

Appeared in: INI-CET EXAM -2025

Explanation

• The sympathetic chain contains the second-order (preganglionic) neurons of the oculosympathetic pathway.
• These preganglionic fibers supply both the structures of the eye (for pupil dilation and eyelid elevation) and the sweat glands of the face.
• A lesion or compression of the sympathetic chain interrupts the signal to both pathways before they diverge.
• This results in the classic presentation of Horner's syndrome (miosis, ptosis) combined with facial anhidrosis, as described in the question.

Why Other Options Were Wrong

• Option B: The internal carotid plexus contains postganglionic sympathetic fibers that travel to the eye. The fibers for facial sweating travel with the external carotid artery. A lesion here would cause Horner's syndrome but would spare facial sweating.
• Option C: The vagus nerve (Cranial Nerve X) is primarily a parasympathetic nerve and is not part of the oculosympathetic pathway that causes Horner's syndrome.
• Option D: While a pathology of the common carotid artery (like a dissection or aneurysm) can cause Horner's syndrome by compressing adjacent structures, the artery itself is not the affected neural structure. The sympathetic chain runs alongside the carotid artery, and it is the compression of this chain that produces the symptoms.

Related Visual

• Visual 1: Diagram - The three-neuron oculosympathetic pathway. This visual should clearly show the first, second (preganglionic), and third (postganglionic) order neurons. It must illustrate how postganglionic fibers for sweating branch off to follow the external carotid artery, while fibers for the eye follow the internal carotid artery, clarifying why a preganglionic lesion causes anhidrosis.

Clinical Relevance

• Nursing practice connection: Use the key finding related to Localization of Lesion in Horner's Syndrome to guide bedside assessment, documentation, and the next nursing action.
• Accurately localizing the lesion in Horner's syndrome is critical for guiding further diagnostic workup. The presence of anhidrosis points towards a preganglionic lesion.
• Preganglionic lesions can be caused by serious conditions such as a Pancoast tumor (a tumor at the apex of the lung), neck trauma, or thoracic surgery, requiring urgent imaging of the neck and chest.
• What if? If the patient had developed Horner's syndrome acutely with neck pain, a postganglionic lesion due to carotid artery dissection would be a primary concern, even without anhidrosis. This would require urgent vascular imaging (CTA or MRA).

How to Approach the Question

• First, identify the key clinical signs presented in the question: Horner's syndrome (implying ptosis and miosis) and facial anhidrosis (absence of sweating).
• Recall the basic anatomy of the three-neuron oculosympathetic pathway.
• Focus on the key differentiating feature: the point at which the nerve fibers for ocular function and facial sweating diverge. This occurs after the superior cervical ganglion.
• Recognize that the presence of both ocular signs and facial anhidrosis means the lesion must be 'proximal' or 'before' this split.
• Evaluate the options based on this understanding. A lesion of the 'sympathetic chain' is preganglionic, while a lesion of the 'internal carotid plexus' is postganglionic.
• Conclude that the sympathetic chain is the only option that would produce the full constellation of symptoms described.

Concept Tested & Keywords

• Concept Tested: Localization of Lesion in Horner's Syndrome
• Stem keywords: Horner's syndrome, absence of sweating, anhidrosis, compressed
• Lead-in keywords: most likely
• Clinical cues: The combination of Horner's syndrome with facial anhidrosis is a key localizing sign.

Question ID

QsGERdvIpeBx3HqWu8s-Jy

Copy ID