Causes And Sites Of Lesions Of The Sixth Cranial Nerve

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1. Within the pons, causes include a. Multiple sclerosis b. Infarct c. Mass (eg, glioma or tuberculoma)

d. Wernicke's syndrome

Look for ipsilateral

• Seventh nerve lesion

• Horner's syndrome

• Facial hypesthesia

• Internuclear ophthalmoplegia

Look for contralateral

• Hemiparesis

• Nystagmus (possibly in more than one direction)

• Hemisensory pain and temperature loss in the trunk or limbs

2. At the base of the brain, causes include a. Acoustic neuroma b. Meningitis c. Subarachnoid hemorrhage d. Compression of an aneurysm or anomalous vessel e. Basal meningioma f. Nasopharyngeal carcinoma g. Chordoma h. Wegener's granulomatosis

Look for signs of involvement of the fifth, seventh, and eighth cranial nerves.

3. In relation to the petrous portion of the temporal bone, causes include a. Infection, fracture, or tumor of the petrous bone

Look for pain, paresthesia, or hyperesthesia of the face (same side) and deafness.

4. In the cavernous sinus/superior orbital fissure, causes include a. Aneurysm (carotid)

b. Carotid—cavernous fistula (trauma)

c. Tumor—pituitary, meningioma, or nasopharyngeal carcinoma d. Tolosa-Hunt syndrome e. Cavernous sinus thrombosis f. Mucormycosis (in diabetics)

g. Herpes zoster

Look for signs of involvement of the third and fourth cranial nerves as well as first and second divisions of the fifth.

5. In the orbit, causes include a. Tumor b. Trauma

6. Common and not so common causes, but with an uncertain site, include a. Postviral infection (especially in children)

b. Diabetes c. Hypertension d. Postlumbar puncture or myelogram e. Increased intracranial pressure f. Migraine g. Arteritis or angiitis of sarcoidosis h. Fisher variant of Guillain-Barre syndrome

7. Other causes of abduction defect include a. Thyroid ophthalmopathy b. Myasthenia gravis c. Orbital pseudotumor d. Trauma e. Duane's syndrome f. Convergence spasm

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