NBME 15 Aneurysm of the posterior communicating artery (NBME Answers)

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NBME 15 Answers

nbme15/Block 2/Question#9 (reveal difficulty score)
A 67-year-old man is brought to the physician ...
Aneurysm of the posterior communicating artery 🔍 / 📺 / 🌳 / 📖
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submitted by ∗ergogenic22(401)

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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.

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cheesetouch Compression of superior cervical ganglion -> Horner's syndrome -> ptosis, miosis, anhidrosis, would NOT have dilated pupil. +3

jmd2020 Aneurysm of the PCA would compress the oculomotor NERVE, not the nucleus (just fyi) +4

trazobone I appreciate u cheesetouch +

lovebug FA2019 P529 +

aashkad CN III controls the sphincter pupillae (responsible for pupillary constriction) so damage to CN III would cause the dilated pupil +

+3 upvote downvote
submitted by ∗trazobone(97)

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

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

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shieldmaiden oculomotor nerve* +

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