Oculomotor nerve schwannoma located in the oculomotor cistern

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    Keywords:

    1. Introduction rn and the CS.

    Surgical Neurology 67Abbreviations: CS, cavernous sinus; ICA, internal carotid artery;

    MRI, magnetic resonance imaging; OS, oculomotor schwannoma.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

    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 muscles0090-3019/$ see fro

    doi:10.1016/j.surneu.2

    Caddebostan, Istanbul

    216 578 0575.

    E-mail address: nfissure. 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.

    Cavernous sinus; Oculomotor cistern; Oculomotor nerve; Schwannoma

    segment within the interpeduncular cisteand the roof of the CS was opened just above the oculomotor nerve toward the superior orbitalnerve 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,for cavernous OSs.

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

    Necmettin Tanriover, MDa,4, Rahsan KSiyavus Muhammedreza

    aDepartment of Neurosurgery, Cerrahpasa MedicbAcVbadem BakVrkoy Hos

    Received 3 January 20

    Abstract Background: OSs are extremely rare tumors, m

    CS. We report an OS located predominantly w

    surrounds the nerve for a short distance in the rnt matter D 2007 Elsevier Inc. All rights reserved.

    006.06.012

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

    ctan27@yahoo.com (N. Tanriover).sm

    cated in the oculomotor cistern

    erdere, MDa, Ali M. Kafadar, MDa,

    Db, Ziya Akar, MDa,b

    ulty, Istanbul University, 34303 Istanbul, Turkey

    34303 Istanbul, Turkey

    ccepted 11 May 2006

    ften located in the interpeduncular cistern or the

    the oculomotor cistern, the arachnoid sac that

    f the CS. We discuss a possible growth pattern

    (2007) 8388

    www.surgicalneurology-online.comrevealed right oculomotor nerve palsy. The right pupil was

    irregularly shaped and mydriatic. The right optic disc4 Corresponding author. Mehtap sok. Cicek cVkmazV. UlaY Apt. No:2/6,appeared pale upon ophthalmoscopic examination. Exami-

    nation of her left eye was normal.

  • 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. 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.

    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

    N. Tanriover et al. / Surgical Neurology 67 (2007) 838884posterior 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.

  • 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

    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 anatomyoculomotor 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) 8388 85appeared 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.

  • al Nepeduncle 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 schwannomalocated 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.

    N. Tanriover et al. / Surgic86Because the cavernous OSs are extremely rare, they can

    easily be misinterpreted as a meningioma, trochlear ortrigeminal 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 c...

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