Case report

Oculomotor nerve schwannoma: MRI appearance

Sattam S. Lingawi

Radiology Department, The University Hospital, King Abdulaziz University, PO Box 7363, Jeddah 21462, Saudi Arabia

Received 1 December 1999; accepted 30 May 2000

Abstract

The magnetic resonance imaging (MRI) appearance of oculomotor nerve schwannoma is presented. The lesion appears as a 5-mm mass

arising from the cisternal segment of the nerve and is isointense to brain parenchyma on T1- and hypointense on T2-weighted images.

Intravenous Gadolinium injection results in intense enhancement of the tumor. Despite its rare incidence, schwannoma should be included in

the differential diagnosis of nodular enhancement of the oculomotor nerve. D 2000 Elsevier Science Inc. All rights reserved.

Keywords: Oculomotor nerve; Schwannoma; Cranial nerves; Magnetic resonance imaging

1. Introduction

Cranial nerves schwannomas arise commonly from the

vestibulocochlear and trigeminal nerves. These lesions ap-

pear to have a predilection to sensory nerves, and involve-

ment of the oculomotor nerve is very rare. Majority of these

lesions occur as part of the cranial manifestations of type II

neurofibromatosis. Only 17 cases of isolated oculomotor

nerve schwannomas have been reported. This case report

describes the magnetic resonance imaging (MRI) appear-

ance of an isolated oculomotor schwannoma that was

incidentally discovered during investigations of possible

intracranial metastasis from testicular semminoma.

2. Case report

A 53-year-old man presented with persistent headache of

3-month duration. Neurological and ophthalmological ex-

amination did not reveal any abnormality. No family history

of neurofibromatosis was elicited. The patient has finished a

successful therapy for testicular semminoma with abdom-

inal lymph node metastasis. MRI of the head revealed a 5-

mm solid mass arising from the cisternal segment of the

right oculomotor nerve. The mass is isointense to brainstem

on T1- and hypointense on T2-weighted images and en-

hances strongly and homogeneously after Gadolinium ad-

ministration (Fig. 1). No other abnormalities were detected.

The mass was totally resected via a right anterior temporal

approach. Intraoperatively, the mass was found to be arising

from the cisternal segment of the oculomotor nerve. The

cavernous sinus was not involved, and no other neural

attachments were identified. The nerve trunk was identified

and the tumor was shaved off using a nerve-sparing tech-

nique. Six months post-operatively, the nerve function

remained intact. The histopathological examination of the

tumor was consistent with a schwannoma.

3. Discussion

Schwannomas account for 8±10% of primary intracra-

nial tumors. Most schwannomas arise from sensory nerves,

the superior division of the vestibular nerve being the most

common site. However, schwannoma of the oculomotor

nerve is very rare in non-neurofibromatosis patients [1].

Only 17 cases of isolated oculomotor nerve schwannomas

have been reported in the literature.

The nuclei of the oculomotor nerve are located in the

periaquiductal gray matter of the midbrain tectum. The

nerve passes ventrally through the red nucleus and exits

the brainstem from the medial aspect of the cerebral

peduncle into the interpeduncular cistern. It courses ante-

riorly and passes through the lateral wall of the cavernous

sinus. Eventually, the nerve enters the orbit through the

superior orbital fissure and supplies all extraocular muscles

except the lateral rectus and the superior oblique musclesE-mail address: tersam2@yahoo.com (S.S. Lingawi).

Journal of Clinical Imaging 24 (2000) 86± 88

0899-7071/00/$ ± see front matter D 2000 Elsevier Science Inc. All rights reserved.

PII: S0 8 9 9 - 7 0 7 1 ( 0 0 ) 0 0 1 80 - 7

[2,3]. MRI is now considered the diagnostic method of

choice for visualization and evaluation of cranial nerve

abnormalities. Typically, cranial nerve schwannomas would

appear isointense to brainstem on both T1- and T2-weighted

images. Cystic changes are commonly seen in schwanno-

mas, which result in the increased T2 signal intensity of

these lesions. Gadolinium-enhanced dynamic MRI reveals a

gradual increase pattern in time intensity curve of schwan-

nomas. In comparison, meningiomas have a higher tendency

for calcifications, lower tendency for cystic changes and

show a strong early enhancement with prolonged slow

contrast release [3].

Literature review revealed only 17 other similar cases

[4±8]. Analysis of these cases revealed that one case was

diagnosed on autopsy [5] and three cases were incidental

discoveries (similar to this case) while neuroimaging was

Fig. 1. Axial non-enhanced T1-weighted (a), T2-weighted (b) and Gadolinium-enhanced T1-weighted (c) images at the level of the brainstem. A small soft

tissue mass is present in the interpeduncular cistern abutting the medial surface of the right cerebral peduncle. It is along the expected course of the cisternal

segment of the right oculomotor nerve (arrow in a, b and c). The mass is isointense to gray matter on T1-weighted (a), mildly hypointense on T2-weighted

(b) and enhances strongly and homogeneously on the post-Gadolinium T1-weighted (c) images. The normal left oculomotor nerve is seen on the T2-

weighted (b) and post-Gadolinium T1-weighted (c) image (arrowhead). No midbrain invasion seen. Sagittal enhanced T1-weighted image (d) demonstrating

the intensely and homogeneously enhancement of the mass (empty arrow), as well as its relation to the cisternal segment of the right oculomotor nerve

(curved arrow).

S.S. Lingawi / Journal of Clinical Imaging 24 (2000) 86±88 87

being done for other purposes [4,8]. The most common

presenting symptom in the other 13 cases is oculomotor

nerve palsy of variable degrees. Other common presenting

symptoms were headache, hemiparesis and cranial nerves

IV, V and VI deficits (from mass effect). It also appears that

the lesion size does not correlate with the degree of

oculomotor nerve deficit. The most common site of these

lesions is the cisternal segment of the nerve; however,

parasellar, suprasellar and cavernous extension have been

reported in large lesions. There appears to be no sex or age

predilections and the range of age of symptom onset varies

between 11 and 66 years.

Due to the deep location of these lesions and the close

proximity to critical structures, pre-operative localization

with accurate evaluation of the lesion extent, as well as the

involvement of other neural structures is crucial for opera-

tive planning. Since total resection of the tumor is often not

possible without nerve sacrifice, the benefits and the risks of

the surgery have to be well explained and discussed with the

patient. This issue might not be critical in patients with

complete oculomotor nerve palsy since nerve function rarely

recovers. However, if the patient has only minor or no nerve

palsy, nerve-sparing surgery should be attempted even if

that entails subtotal resection of the tumor. In our case, the

tumor MRI characteristics, location and patient symptoms

are all compatible with the reported literature. The known

history of testicular semminoma raised the issue of possible

metastatic deposit.

In conclusion, isolated oculomotor nerve tumors are very

rare. The differential diagnosis includes meningiomas, lym-

phoma, metastasis and inflammatory conditions such as

sarcoidosis. MRI characteristics may help in narrowing the

differential diagnosis. Nerve-sparing surgery should always

be attempted if surgery is contemplated.

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