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44 year-old man with double vision
Digital Journal of Ophthalmology 2006
Volume 12, Number 4
December 3, 2006
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Joseph Rizzo, M.D. | Harvard Medical School/Massachusetts Eye and Ear Infirmary
Corey Westerfeld, M.D. | Harvard Medical School/Massachusetts Eye and Ear Infirmary
Diagnosis and Discussion
Left fourth nerve palsy secondary to a left fourth nerve schwannoma.

Schwannomas comprise 8% of intracranial neoplasms and usually involve the 7th or 8th cranial nerves. Schwannomas may also involve the fifth cranial nerve, presenting as orbital masses in adults. They often occur in the setting of Neurofibromatosis Type II. A recent paper evaluating fourth nerve palsies reviewed 221 cases of fourth nerve palsies. 68 of the cases were found to have an isolated 4th nerve palsy. Of those, 6 were due to a radiologically identifiable 4th nerve schwannoma. A mean follow-up of 15 months found that none of the patients developed any additional symptoms or signs of cranial nerve or brainstem involvement.(3) These findings suggest that these patients can simply be followed over time with low risk of further neurologic consequence.

Interestingly, the neurosurgical literature reports many patients with fourth nerve schwannomas in association with other neurologic findings, often necessitating surgical excision.(4) It is likely that the patients who present to neurosurgeons represent a different subset of patients whose tumors are often larger and in closer proximity to brainstem structures, thus producing other signs. To date, patients who present with isolated fourth nerve palsies secondary to a schwannoma have not been shown to progress to further brainstem involvement.

Also, of note, our patient did have high vertical fusional amplitudes. We postulate that this is due to the relatively long period during which the schwannoma had been present resulting in a clinical picture similar to that of a congenital fourth nerve palsy. As such, it is possible that some portion of patients diagnosed with a “congenital” fourth nerve palsy, if imaged, would demonstrate a fourth nerve schwannoma. This does not significantly alter management, although, it does provide both patient and physician with a diagnostic conclusion for the clinical picture.

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