Surgical Neurolo

Neoplasm

Oculomotor nerve schwannoma located in the oculomotor cistern

Necmettin Tanriover, MDa,4, Rahsan Kemerdere, MDa, Ali M. Kafadar, MDa,

Siyavus Muhammedrezai, MDb, Ziya Akar, MDa,b

aDepartment of Neurosurgery, Cerrahpasa Medical Faculty, Istanbul University, 34303 Istanbul, TurkeybAcVbadem BakVrkoy Hospital, 34303 Istanbul, Turkey

Received 3 January 2006; accepted 11 May 2006

Abstract Background: OSs are extremely rare tumors, most often located in the interpeduncular cistern or the

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doi:10.1016/j.surneu.2

Abbreviations: C

MRI, magnetic resona

4 Corresponding a

Caddebostan, Istanbul

216 578 0575.

E-mail address: n

CS. We report an OS located predominantly within the oculomotor cistern, the arachnoid sac that

surrounds the nerve for a short distance in the roof of the CS. We discuss a possible growth pattern

for cavernous OSs.

Case Description: We report the case of a 34-year-old woman presenting with a right oculomotor

nerve palsy. Magnetic resonance imaging revealed a mass within the borders of the roof of the CS

extending forward toward the superior orbital fissure. A right pterional approach was undertaken,

and the roof of the CS was opened just above the oculomotor nerve toward the superior orbital

fissure. Although the part of the OS inside the oculomotor cistern was excised completely while

preserving the anatomical continuity of the nerve, a subtotal removal was performed for the more

anterior part of the tumor toward the superior orbital fissure. At 5 months follow-up, her third nerve

paresis had improved dramatically.

Conclusions: Resection of cavernous OSs within the oculomotor cistern, where the third nerve is

clearly separated from the adjacent neurovascular structures, is feasible with functional preservation

of the nerve. The chance of occurrence of the nerve palsy may increase as the resection proceeds

more anteriorly toward the superior orbital fissure.

D 2007 Elsevier Inc. All rights reserved.

Keywords: Cavernous sinus; Oculomotor cistern; Oculomotor nerve; Schwannoma

1. Introduction

Schwannomas constitute about 7% of all intracranial

tumors and commonly arise from vestibulocochlear and

trigeminal nerves [17,22,32,33]. The sensory division of

cranial nerves is most likely to be affected [32]. Motor

nerve schwannomas arising from ocular nerves are very

rare in the absence of neurofibromatosis type II [13].

Only 32 cases of isolated schwannomas arising from

the oculomotor nerve have been reported in the literature

[1-5,8-10,12-19,21-30,33-35,37-40]. The most common

site of occurrence for these lesions is the neuronal

nt matter D 2007 Elsevier Inc. All rights reserved.

006.06.012

S, cavernous sinus; ICA, internal carotid artery;

nce imaging; OS, oculomotor schwannoma.

uthor. Mehtap sok. Cicek cVkmazV. UlaY Apt. No:2/6,

, Turkey 34728. Tel.: +90 216 368 3422; fax: +90

ctan27@yahoo.com (N. Tanriover).

segment within the interpeduncular cistern and the CS.

We report the case of an OS located predominantly

within the oculomotor cistern, the arachnoid sac that

surrounds the nerve for a short distance in the roof of

the CS and extends forward to where the nerve passes

under the anterior clinoid process.

2. Case report

A 34-year-old woman presented to our clinic with

intermittent headaches for the last 6 months. She had

developed ptosis, an enlarged pupil on the right side, and

experienced lateral deviation of her right eye 3 weeks before

her admission. Examination of the extraocular muscles

revealed right oculomotor nerve palsy. The right pupil was

irregularly shaped and mydriatic. The right optic disc

appeared pale upon ophthalmoscopic examination. Exami-

nation of her left eye was normal.

gy 67 (2007) 83–88

Fig. 1. A: Gadolinium-enhanced axial MRI view showing enhancing mass

(yellow arrow) within the oculomotor cistern located in the right CS and

lateral deviation of the eye. B and C: Coronal T2-weighted MRI images at

different levels demonstrating location of the tumor (yellow arrow) in

relation to the ICA and the roof of the CS.

N. Tanriover et al. / Surgical Neurology 67 (2007) 83–8884

An MRI scan demonstrated a mass lesion predominantly

within the roof of the CS and extending up into the superior

orbital fissure. The lesion filled part of the roof of the CS

lateral to the clinoid and supraclinoid segments of the

ICA (Fig. 1). The lesion was hypointense in T1- and

T2-weighted images and showed some enhancement after

Fig. 2. A: A cadaveric dissection photograph obtained during a right

pterional exposure. The inset shows the position of the head and skin

incision for the frontotemporal craniotomy. The sylvian fissure has been

widely opened, and the frontal and temporal opercula have been retracted.

The oculomotor nerve enters the roof of the CS within a distance of 1 cm or

less posterior to the initial supraclinoid ICA and slightly lateral to the

posterior clinoid process. The approximate location of the oculomotor

cistern is delineated by blue broken lines. B: Intraoperative photograph of

the right pterional exposure. The proximal part of the sylvian fissure has

been opened, and the right optic nerve, the supraclinoid segment of the

ICA, and the oculomotor nerve have been exposed. The roof of the CS has

been opened above the oculomotor nerve, and the schwannoma located in

the oculomotor cistern has been exposed (yellow arrow). A1 indicates

A1 segment of the anterior cerebral artery; Art., artery; Car., carotid; Clin.,

clinoid; CN, cranial nerve; Int., internal; Post., posterior; Temp., temporal;

Tent., tentorium.

N. Tanriover et al. / Surgical Neurology 67 (2007) 83–88 85

contrast administration. Differential diagnosis at this time

included a vascular pathology along with benign neoplasms

such as a meningioma or a schwannoma of the cranial

nerves. A magnetic resonance angiography was performed

to eliminate a vascular pathology such as an aneurysm. It

was noted on the magnetic resonance angiogram that the

lesion was avascular.

A right pterional approach was undertaken, and the

sphenoid ridge was widely drilled medially up to the

superolateral edge of the superior orbital fissure.

The extradural dissection continued, and the meningo-

orbital artery was exposed and sacrificed at this point. The

sylvian fissure was opened from distal to proximal

orientation, and the ICA bifurcation, the optic nerve, and

the proximal parts of the posterior communicating and

anterior choroidal arteries were exposed. The part of the

oculomotor nerve within the interpeduncular cistern was

normal in appearance and free of tumor infiltration.

Adjacent to the posterior clinoid process, the third nerve

appeared to be edematous and thickened at the point of

entrance along the roof of the CS. An incision of

approximately 2 cm along the roof of the CS just above

the oculomotor nerve exposed the tumor located in the

oculomotor cistern (Fig. 2). Although the tumor was firm

and moderately vascular, the part of the oculomotor nerve

within the cistern could be separated from the exophytic part

of the tumor and could be removed. Because of the intimate

relationship between the tumor and the oculomotor,

trochlear and ophthalmic nerves near the superior orbital

fissure, a complete resection was not attempted for the

more anterior part of the tumor toward the superior orbital

fissure. The tumor was removed subtotally because of

concern about inducing a permanent oculomotor palsy. The

anatomical continuity of the nerve was preserved at the end

of the operation.

Fig. 3. Lateral view of a stepwise anatomical dissection of the CS and

adjacent superior orbital fissure demonstrating the right oculomotor cistern

and the course of the oculomotor nerve. A: The cerebral hemisphere, the

dura over the anterior clinoid, and the outer layer of dura in the lateral CS

wall have been removed. The oculomotor nerve enters the roof of the CS

and passes forward above the trochlear nerve to reach the lower surface of

the anterior clinoid process. B: The anterior clinoid has been removed, and

the optic nerve has been elevated to display the relationship between the

oculomotor nerve and the trochlear and ophthalmic nerves. The oculomotor

nerve rests in a cistern (marked with blue oblique lines) within the sinus

roof, in which the nerve is separated below from the trochlear nerve, and

travels a variable distance along the course of the nerve. The trochlear nerve

passes medially above the oculomotor and ophthalmic nerves as it

approaches toward the superior orbital fissure. C: The oculomotor nerve

has been retracted laterally to display the medial border of the oculomotor

cistern, which is adjacent to the clinoidal segment of the ICA. The carotid-

oculomotor membrane (marked with a blue asterisk) demarcates the medial

border of the oculomotor cistern and separates the upper surface of the

oculomotor nerve from the lower surface of the anterior clinoid. The site at

which the carotid-oculomotor membrane is located does not adhere to the

arterial wall and, therefore, creates an additional space within the cistern.

Ant. indicates anterior; Cav., cavernous; Oph., ophthalmic; Pit., pituitary;

Seg., segment; V1, ophthalmic nerve; V2, maxillary nerve.

Histopathological examination confirmed the diagnosis

of schwannoma. The postoperative course was uneventful,

and the patient was discharged on fourth operative day.

At 5 months follow-up, her third nerve paresis had

improved dramatically.

3. Discussion

3.1. Surgical anatomy—oculomotor cistern

The oculomotor nerve arises in the interpeduncular

cistern from the midbrain on the medial side of the cerebral

N. Tanriover et al. / Surgical Neurology 67 (2007) 83–8886

peduncle and courses between the posterior cerebral and

superior cerebellar arteries [39]. The nerve courses medial to

the uncus before piercing the dura at the roof of the CS. The

oculomotor nerve enters the roof of the CS approximately

5 mm posterior to the initial supraclinoidal segment of the

ICA and slightly lateral to the posterior clinoid process

(Fig. 3) [7,31]. A short length of the oculomotor nerve is

surrounded by a dural cuff to create an arachnoid filled

space at the roof of the CS, the oculomotor cistern. The

oculomotor nerve extends forward in its cistern to the point

where the nerve reaches the posteroinferior edge of the

anterior clinoid process and eventually travels anteriorly in

the lateral wall of the CS toward the superior orbital fissure.

The medial border of the oculomotor cistern, the carotid-

oculomotor membrane, is adjacent to the clinoidal segment

of the ICA. The carotid-oculomotor membrane (Fig. 3)

separates the upper surface of the oculomotor nerve from the

lower surface of the anterior clinoid. The membrane does

not densely fuse to the wall of the clinoidal segment of the

ICA and, therefore, provides an additional arachnoidal space

within the oculomotor cistern for further tumor growth.

The oculomotor cistern provides a sufficient space

for a lateral mobilization of the third nerve because of its

loose medial connection with the ICA. The opening of

the oculomotor cistern has been proposed to obtain

enough area for removing the posterior clinoid process

through the carotid-oculomotor space during the trans-

cavernous approaches into interpeduncular and prepontine

cisterns [31,39,41].

3.2. Oculomotor schwannoma—located mainly within the

oculomotor cistern

The first report of an isolated oculomotor nerve sheath

tumor was published by Kovacs [20] at an autopsy in 1927.

Clinical findings in OSs occur almost always with a certain

degree of oculomotor palsy [16,39]. Cavernous OSs can

lead to paresis of any nerve of the CS or a clinicoradio-

logical orbital apex syndrome, whereas cisternocavernous

OSs often cause symptoms of intracranial hypertension

[5,13]. These findings were consistent with the present case.

Magnetic resonance imaging is considered the diagnostic

method of choice for visualization and evaluation of cranial

nerve abnormalities. Because of the close proximity of the

cranial nerve schwannomas to critical structures, preopera-

tive localization with accurate evaluation of the extent

and growth pattern of the lesion is crucial for operative

planning. The cranial nerve schwannomas appear iso- or

hypointense to brainstem on both T1-weighted images and

hypointense T2-weighted images, along with a marked

contrast enhancement [23]. The preoperative diagnosis in

our case was challenging because of lack of marked contrast

enhancement. The lesion was hypointense in T1- and

T2-weighted images and showed only minor enhancement

after contrast administration.

Because the cavernous OSs are extremely rare, they can

easily be misinterpreted as a meningioma, trochlear or

trigeminal schwannoma, chordoma, lymphoma, metastasis,

or inflammatory condition, such as sarcoidosis [13,16,23].

Although the roof of the CS may be affected in most of

these other pathologies, the oculomotor cistern would not be

the primary site of focus. Careful preoperative examination

of the pattern of tumor growth along the roof of the CS and

its relation with the oculomotor cistern may be helpful in

preoperative evaluation.

Literature review revealed 32 cases of OSs, most of

which were located in the interpeduncular cistern and the

CS [1-5,7-10,12-19,21-30,33-35,37-41]. However, parasel-

lar and suprasellar extensions have been reported for large

lesions [23]. These tumors can also occur in the prepontine

cistern, parasellar region, or the orbital apex [13]. Celli et al

[5] categorized OSs into cisternal, cavernous, and cisterno-

cavernous groups.

Previous reports do not delineate the exact location of the

schwannoma within the CS. The maximum bulge of the

tumor in the present case was within the oculomotor cistern.

The color change on the oculomotor nerve as it pierces the

dura along the roof of the CS was apparent, and the most

prominent part of the tumor was located within a centimeter

from this point. Opening the oculomotor cistern exposed the

tumor, and an anterior extension toward the anterior clinoid

was also noted. As in the present case, the oculomotor

cistern may provide a convenient space for OS to expand at

the region of the CS. Therefore, the OSs previously

categorized within the cavernous group and the cavernous

part of the tumors within the cisternocavernous group may,

in fact, be primarily located within the oculomotor cistern.

Any damage to the fourth and sixth cranial nerves can

better be tolerated than the third nerve because of multiple

functions of the nerve that innervates multiple muscles

[6,36]. Even when the third nerve is damaged because of an

expanding aneurysm, in which the nerve remains in

anatomic continuity, aberrant or misdirected regeneration

occurs in up to 84% of patients [6,36]. The third nerve

seems to be more susceptible to permanent damage during

microsurgical removal of the cranial nerve schwannomas

because the oculomotor nerve provides highly differentiated

function to multiple ocular muscles compared to that of the

fourth and sixth cranial nerves, which innervate only one

ocular muscle [1,6,36].

Surgical treatment is indicated for large OSs that present

in association with consciousness disturbance, other cranial

nerve signs, or hemiparesis due to mass effect [1]. Although

a wait-and-see policy is recommended in asymptomatic

cases, symptomatic cavernous OSs may be appropriate for

microsurgical excision [16,33]. Given the results of previous

reports, the functional results after radical resection are

limited, and total resection of the cavernous OSs is often not

possible without nerve sacrifice. The resection of the tumor

within the oculomotor cistern, where the third nerve is

clearly separated from the adjacent neurovascular structures,

and a follow-up for the more anterior residual part of the

tumor would be an appropriate treatment modality. Another

N. Tanriover et al. / Surgical Neurology 67 (2007) 83–88 87

alternative would be the radiosurgical treatment for the

remaining tumor. Because the radiobiological mechanism

for growth control of schwannomas via radiosurgery is

believed to be a combination of direct tumoricidal effects

and delayed intratumoral vascular obliteration, radiosurgery

should also be effective in OSs, which originate from

Schwann cells, as in vestibular schwannoma [11]. Both of

these treatment modalities may increase the chance of

functional preservation of the oculomotor nerve.

4. Conclusions

In conclusion, isolated OSs are very rare, and the

oculomotor cistern creates a favorable site for these tumors

to expand for those cases with CS involvement. The part of

the OS within the cistern can be removed while preserving

the anatomical continuity of the nerve. OSs should be

considered in the differential diagnosis among lesions along

the roof of the CS.

Acknowledgments

The anatomical dissections have been performed by one

of the authors (NT) in the Microsurgical Anatomy Labora-

tory at the University of Florida, Department of Neurosur-

gery. The authors thank Ozlem Tanriover, MD, for her

assistance in preparation of the manuscript.

References

[1] Asaoka K, Sawamura Y, Murai H, Satoh M. Schwannoma of the

oculomotor nerve: a case report with consideration of the surgical

treatment. Neurosurgery 1999;45:630-3.

[2] Barat JL, Marchal JC, Bracard S, Auque J, Martin-Beuzart S, Hepner

H. Neurinoma of the oculomotor nerves. A propos of two cases.

Neurochirurgie 1992;38:183-7.

[3] Bataille B, Muckensturm B, Roualdes G, Maissin F, Deglaire R,

Desbordes JM. Neurinome du nerf oculomoteur. A propos d’un cas.

Neurochirurgie 1987;33:405-7.

[4] Broggi G, Franzini A. Value of serial stereotactic biopsies and

impedance monitoring in the treatment of deep brain tumors. J Neurol

Neurosurg Psychiatry 1981;44:397 -401.

[5] Celli P, Ferrante L, Acqui M, Mastronardi L, Fortuna A, Palma L.

Neurinoma of the third, fourth and sixth cranial nerves: a survey and

report of a new fourth nerve case. Surg Neurol 1992;38:216-24.

[6] Forster RK, Schatz NJ, Smith JL. A subtle eyelid sign in aberrant

regeneration of the third nerve. Am J Ophthalmol 1969;67:696-8.

[7] Harris FS, Rhoton Jr AL. Anatomy of the cavernous sinus.

A microsurgical study. J Neurosurg 1976;45:169 -80.

[8] Hashimoto M, Ohtsuka K, Sone A, Nakamura Y, Nakagawa T, Uede

T. A case of neurinoma developing from the oculomotor nerve in

cavernous sinus. Neuroopthalmology (Jpn) 1996;13:299-303.

[9] Hatakeyama H, Saito K, Nagatani T, Patel SJ, Yoshida J. Schwan-

noma in the crural cistern removed without permanent functional

deficits. Case report. Neurol Med Chir (Tokyo) 2003;43:95 -9.

[10] Hiscott P, Symon L. An unusual presentation of neurofibroma of the

oculomotor nerve. Case report. J Neurosurg 1982;56:854 -6.

[11] Huang CF, Kondziolka D, Flickinger JC, Lunsford LD. Stereo-

tactic radiosurgery for trigeminal schwannomas. Neurosurgery 1999;

45:11 -6.

[12] Ishige N, Ito C, Sacki N, Oka N. Neurinoma with intrasellar

extension. A case report. No Shinkei Geka 1985;13:79 -84.

[13] Kachhara R, Nair S, Radhakrishnan VV. Oculomotor nerve

neurinoma: report of two cases. Acta Neurochir (Wien) 1998;140:

1147-51.

[14] Kadota T, Miyawaki Y, Nakagawa II, Ishiguro S, Kuroda C. MR

imaging of oculomotor nerve neurilemmoma. Magn Reson Imaging

1993;11:1071-5.

[15] Kansu T, Ozcan OE, Ozdirim E, Onol B, Gurcay O. Neurinoma of

the oculomotor nerve: case report. J Clin Neuro-ophtalmol 1982;2:

271 -2.

[16] Katoh M, Kawamoto T, Ohnishi K, Sawamura Y, Abe H. Asymp-

tomatic schwannoma of the oculomotor nerve: case report. J Clin

Neurosci 2000;7:458 -60.

[17] Katsumata Y, Maehara T, Noda M, Shirouzu I. Neurinoma of the

oculomotor nerve: CT and MRI features. J Comput Assist Tomogr

1990;14:658-61.

[18] Kawasaki A. Oculomotor nerve schwannoma associated with oph-

thalmoplegic migraine. Am J Ophthalmol 1999;128:658-60.

[19] Kaye-Wilson LG, Gibson R, Bell JE, Steers AJW, Cullen JF.

Oculomotor nerve neurinoma. Early detection by magnetic resonance

imaging. Neuroophtalmology 1994;14:37-41.

[20] Kovacs W. Ueber ein solitares neurinom des nervus oculomotorius.

Zentralbl Allg Pathol 1927;40:518 -22.

[21] Kurokawa Y, Uede T, Honda O, Honmou O. Successful removal of

intracavernous neurinoma originating from the oculomotor nerve.

Case report. Neurol Med Chir (Tokyo) 1992;32:225-8.

[22] Leunda G, Vaquero J, Cabezudo J, Garcia-Uria J, Bravo G.

Schwannoma of the oculomotor nerves: report of four cases.

J Neurosurg 1982;57:563 -5.

[23] Lingawi SS. Oculomotor nerve schwannoma: MRI appearance. J Clin

Imaging 2000;24:86 -8.

[24] Lunardi P, Rocchi G, Rizzo A, Missori P. Neurinoma of the

oculomotor nerve. Clin Neurol Neurosurg 1990;92:333 -5.

[25] Mariniello G, Horvat A, Dolenc V. En bloc resection of an

intracavernous oculomotor nerve schwannoma and grafting of the

oculomotor nerve with sural nerve. J Neurosurg 1999;91:1045-9.

[26] Mehta VS, Singh RVP, Misra NK, Chaudhary C. Schwannoma of the

oculomotor nerve. Br J Neurosurg 1990;4:69-72.

[27] Netuka D, Benes V. Oculomotor nerve schwannoma. Br J Neurosurg

2003;17:168-73.

[28] Niazi W, Boggan JE. Schwannoma of extraocular nerves: survey of

the literature and case report of an isolated third nerve schwannoma.

Skull Base Surg 1994;4:219 -26.

[29] Nogami K, Nishijima M, Endo S, Takaku A. Neurinoma of the

oculomotor nerve. Case report. No Shinkei Geka 1986;14:1237-41.

[30] Okamoto S, Handa H, Yamashita J. Neurinoma of the oculomotor

nerve. Surg Neurol 1985;24:275 -8.

[31] Rhoton Jr AL. The cavernous sinus, the cavernous venous plexus, and

the carotid collar. Neurosurgery 2002;51(Suppl 1):375-410.

[32] Russell DS, Rubinstein LJ. Pathology of tumors of the nervous

system. 5th ed. London7 Edward Arnold; 1989. p. 537.

[33] Sarma S, Sekhar LN, Schessel DA. Nonvestibular schwannomas of

the brain: a 7-year experience. Neurosurgery 2002;50:437-48.

[34] Schubiger O, Valavanis A, Hayek J, Dabir K. Neuroma of the

cavernous sinus. Surg Neurol 1980;13:313-6.

[35] Schultheiss R, Kristif R, Schramm J. Complete removal of an

oculomotor nerve neurinoma without permanent functional deficit.

Ger J Ophthalmol 1993;2:228 -33.

[36] Sekhar LN, Lanzino G, Sen CN, Pomonis C. Reconstruction of the

third through sixth cranial nerves during cavernous sinus surgery.

J Neurosurg 1992;76:935-43.

[37] Shen WC, Yang DY, Ho WL, Ho YJ, Lee SK. Neurilemmoma of the

oculomotor nerve presenting as an orbital mass: MR findings. AJNR

Am J Neuroradiol 1993;14:1253-4.

[38] Shuangshoti S. Neurilemmoma of the oculomotor nerve. Br J

Ophthalmol 1975;59:64-6.

N. Tanriover et al. / Surgical Neurology 67 (2007) 83–8888

[39] Sindou M, Pelissou I. Trigeminal neurinomas. A special type of

cavernous sinus tumors. In: Dolenc VV, editor. The cavernous sinus.

Wien7 Springer; 1987. p. 355 -76.

[40] Takano S, Endo M, Miyasaka Y, Yada K, Ohwada T, Takagi H.

Neurinoma of the oculomotor nerve. Case report. Neurol Med Chir

(Tokyo) 1990;30:132-6.

[41] Yasuda A, Campero A, Martins C, Rhoton Jr AL, Oliveira E, Ribas

GC. Microsurgical anatomy and approaches to the cavernous sinus.

Neurosurgery 2005;56(1 Suppl):4 -27.

Commentary

The authors present a nicely written and illustrated case

of an oculomotor nerve schwannoma. The presentation,

imaging, and relevant anatomy is well described. The

imaging features are not typical of a schwannoma and

therefore are especially useful. The authors have provided

the reader with a nice reminder to consider this unusual

lesion in their differential diagnosis in the parasellar area.

I agree with the treatment they performed. Aberrant

regeneration is a real problem in the oculomotor nerve,

which can render the patient quite disabled with diplopia

that is difficult to correct. Therefore, complete resection and

a nerve graft are not functionally useful to the patient.

Chandranath Sen, MD

Department of Neurosurgery

St. Luke’s-Roosevelt Hospital Center

New York, NY 10019, USA