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NBME 15 Answers

nbme15/Block 2/Question#9

A 67-year-old man is brought to the physician ...

Aneurysm of the posterior communicating artery

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He has a down and out pupil, caused by CN III palsy. His gaze is due to unopposed action of the lateral rectus and superior oblique; ptosis due to denervation of levator palpebrae superiosis.

The only injury listed that could cause a CN III palsy is aneurysm of the PCA compressing the ocularmotor nucleus.