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NBME 21 Answers

nbme21/Block 3/Question#40

A 65-year-old woman undergoes surgical repair of an ...

Area labeled ‘A’ (Cranial nerve 3)

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submitted by hayayah(414),

Note: The abducens n. is actually the nerve most likely to be damaged by an expanding internal carotid aneurysm in the cavernous sinus but they give you specific CN3 function in this question.

hungrybox  One pupil larger than the other indicates damage to the pupillary light reflex - afferent: CN II, efferent: CN III. +3  
cienfuegos  A little more info regarding other sxs (via UW): -cavernous carotid aneurysm: small usually asx, enlargement can cause u/l throbbing HA &/or CN deficits. VI most common thus ipsilateral lateral rectus weakness, can cause esotropia = inward eye deviation & horizontal diplopia worse when looking toward lesion -can also damage III, IV and V1/2 -can occasionally compress optic nerve or chiasm thus ipsilateral monoocular vision loss or non-specific visual acuity decrease +1  

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submitted by dr.xx(47),

Structures within the outer (lateral) wall of the compartment from superior to inferior: Oculomotor nerve Trochlear nerve Ophthalmic and maxillary branches of the trigeminal nerve Structures passing through the midline (medial) wall: Abducens nerve Internal carotid artery accompanied by the Internal carotid plexus