Which statement about the trochlear nerve is correct?

• A It emerges from the ventral surface of the midbrain and does not decussate
• B It passes through the cavernous sinus medial to the internal carotid artery
• C It innervates the superior oblique of the ipsilateral eye without crossing
• D It is the only cranial nerve that emerges from the dorsal aspect of the brainstem and completely decussates ✓

Explanation

The trochlear nerve is unique: it is the only cranial nerve to exit the dorsal brainstem, emerging just below the inferior colliculus, and all its fibres decussate in the superior medullary velum, so each nerve supplies the contralateral superior oblique. It also has the longest intracranial course. It runs in the lateral wall of the cavernous sinus, not medial to the carotid artery.

Reference: Gray's Anatomy for Students, 4th ed.

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