What is the role of MRI/MRA in the workup of third cranial nerve palsy (oculomotor cranial nerve palsy)?

Updated: Oct 08, 2018
  • Author: James Goodwin, MD; Chief Editor: Andrew G Lee, MD  more...
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Answer

MRI is a more sensitive imaging technique than CT scan for the evaluation of a nonaneurysmal cause of third nerve palsy (inflammation, demyelination, ischemic infarction, abscess, or tumor).

MRI is also the procedure of choice for demonstrating meningeal and dural inflammation and infiltration.

Abnormal signal intensity and enhancement in the intracavernous portion of the third cranial nerve has been demonstrated in a case of herpes zoster with third cranial nerve palsy. [25]

Special MR sequences such as diffusion-weighted imaging (DWI) can demonstrate a small and acute infarct in the midbrain involving the intraparenchymal segment of the third cranial nerve in a patient with acute onset third cranial nerve palsy. [26]

MRI/MRA also gives more specific information than CT scan on vascular flow patterns and is better for picking up lesions in the cavernous sinus, including aneurysm.

MRA using 1.5-Tesla or lower strength magnet is probably not adequate to rule out berry aneurysm causing third cranial nerve palsy, although 3-Tesla MRA with special attention to the circle of Willis can be definitive in this regard because of enhanced resolution.


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