Which of the following is a post-ganglionic etiology of Horner's syndrome?

• A. Neck trauma
• B. Pancoast tumor
• C. Cavernous sinus fistula
• D. Cavernous sinus syndrome

Answer: (C)

Horner’s syndrome results from disruption of the oculosympathetic pathway. The fibers before reaching the superior cervical ganglion are called preganglionic; after the ganglion, they are postganglionic and travel with the internal carotid artery into the orbit and facial sweat glands. Lesions before the ganglion, such as neck trauma or a Pancoast tumor, are preganglionic. A cavernous sinus fistula disrupts the sympathetic fibers after they have left the superior cervical ganglion, making it a classic postganglionic cause. While cavernous sinus syndrome can include Horner’s as part of a broader set of cranial nerve issues, the fistula specifically targets the postganglionic fibers, which is why it’s the best answer.