Which of the following cranial nerves does NOT pass through the cavernous sinus?

Explanation

## Cranial Nerves and the Cavernous Sinus **Key Point:** The cavernous sinus is a venous plexus located on either side of the sella turcica. Multiple cranial nerves pass through or within its walls, but the vagus nerve (CN X) is NOT one of them. ### Nerves Passing Through the Cavernous Sinus | Nerve | CN # | Location in Sinus | Course | | --- | --- | --- | --- | | Oculomotor | III | Within lateral wall | Enters via superior orbital fissure | | Trochlear | IV | Within lateral wall | Enters via superior orbital fissure | | Abducens | VI | Within venous space | Runs medial to internal carotid artery | | Ophthalmic (V1) | V | Lateral wall | Enters via superior orbital fissure | | Maxillary (V2) | V | Lateral wall (lower) | Exits via foramen rotundum | **High-Yield:** The mnemonic for nerves in the cavernous sinus lateral wall is **"LMNOP"** — Lateral rectus (CN VI), Medial rectus, Nasociliary, Oculomotor, Posterior ethmoid. However, CN VI actually runs *within* the venous space medial to the internal carotid artery, not strictly in the lateral wall. ### Why Vagus Nerve is Excluded The vagus nerve (CN X) exits the skull via the **jugular foramen** and descends in the neck within the carotid sheath. It does not enter the cavernous sinus at any point. **Clinical Pearl:** Cavernous sinus thrombosis affects the nerves that traverse it — CN III, IV, VI, and V1/V2 — causing ophthalmoplegia and facial sensory loss. Vagus nerve function (phonation, swallowing, gag reflex) is spared.