|Year : 2014 | Volume
| Issue : 4 | Page : 1098-1100
Large oculomotor nerve schwannoma - Rare entity: A case report with review of literature
L Pavan Kumar1, I Monica1, Megha S Uppin2, V Jagannathrao naidu Kotiyala1
1 Department of Radiation Oncology, Nizam's Institute of Medical Sciences, Hyderabad, Telangana, India
2 Department of Pathology, Nizam's Institute of Medical Sciences, Hyderabad, Telangana, India
|Date of Web Publication||9-Jan-2015|
L Pavan Kumar
Department of Radiation Oncology, Nizam's Institute of medical Sciences, Hyderabad - 500 082, Telangana
Source of Support: None, Conflict of Interest: None
Schwannomas commonly arise from peripheral nerves. Intracranial schwannomas are comparatively rare and are seen commonly as vestibular tumors. Oculomotor nerve schwannomas are extremely rare tumors, these are usually symptomatic. A 29 year aged male presented with diplopia and blurring of vision in left eye and found to have an extra-axial lesion at left cavernous sinus involving oculomotor nerve. The excised tumor showed classic morphology of a schwannoma. Postoperatively patient developed complete oculomotor nerve palsy. The tumor recurred after 2 years. It was re-excised followed by radiotherapy.
Keywords: Oculomotor nerve schwannoma, radiation therapy, cranial nerve schwannoma
|How to cite this article:|
Kumar L P, Monica I, Uppin MS, Kotiyala V J. Large oculomotor nerve schwannoma - Rare entity: A case report with review of literature. J Can Res Ther 2014;10:1098-100
|How to cite this URL:|
Kumar L P, Monica I, Uppin MS, Kotiyala V J. Large oculomotor nerve schwannoma - Rare entity: A case report with review of literature. J Can Res Ther [serial online] 2014 [cited 2019 Nov 20];10:1098-100. Available from: http://www.cancerjournal.net/text.asp?2014/10/4/1098/146111
| > Introduction|| |
Schwannomas commonly arise from peripheral nerves. Intracranial schwannomas are comparatively rare and are seen commonly as vestibular tumors. Among nonvestibular schwannomas, trigeminal nerve involvement is common followed by glossopharyngeal, vagal, facial, accessory, hypoglossal, oculomotor, trochlear, and abducens nerve schwannomas, in descending order of frequency. II and V nerve involvement is reported common in neurofibromatosis 2.  Oculomotor nerve schwannomas are extremely rare tumors, these are usually symptomatic. At present, there is no standard treatment for these tumors. In this case report, we highlight a large sporadic oculomotor schwannoma in a 29-year-old patient.
| > Case report|| |
A 29 years aged male presented with diplopia and blurring of vision in left eye of 2 months duration. Examination revealed impaired extraocular movements - up going, down gage and intorsion in left eye, right eye was normal, no other neurological deficit was noted. According to Snellen's chart patients, visual acuity was 6/60. Magnetic resonance imaging (MRI) plain and contrast showed a 3 cm × 2.5 cm × 3 cm well defined, extra-axial lesion at left cavernous sinus lateral wall extending into middle cranial fossa, isointense on T1 and T2, suggestive of giant oculomotor schwannoma [Figure 1]. Patient underwent left orbitozygomatic craniotomy, intraoperatively tumor was protruding superiorly and laterally from cavernous sins, cystic portion decompressed by giving incision over dura lateral to oculomotor the nerve on superior wall of cavernous sinus. Tumor was soft suckable, moderately vascular and arising from the oculomotor nerve before its entry into oculomotor cistern. Near total excision of the tumor was done.
|Figure 1: Magnetic resonance imaging brain postcontrast T1 image showing well defined intensely enhancing, extra-axial lobulated lesion situated posterior to the left orbit apex|
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Postoperative histology showed lesion composed of hypercellular (Antoni A) and hypocellular areas (Antoni B). The hypercellular areas are composed of spindle cells with elongated nuclei arranged in fascicles. Nuclear palisading with verocay bodies was present. Hypocellular areas show loose network of cells in a myxoid background. Thickened and hyalinized vessels are seen. There was no evidence of atypical mitosis or necrosis. These features were consistent with a diagnosis of schwannoma [Figure 2]. The cells showed strong immunohistochemical positivity for S100.
|Figure 2: (a) Lesion composed of spindle-shaped cells arranged in hypercellular (Antoni A) and hypocellular areas (Antoni B) with elongated vesicular nuclei and buckling of nuclei. (b) Interspersed hyalinized thickened blood vessels|
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Postoperatively patient developed complete oculomotor nerve palsy leading to restricted eyeball movements, and complete ptosis left eye. Two years following the surgery, patient came back with diminished vision in the right eye and headache. On examination he had complete ptosis of left eye, visual acuity in right eye - counting finger at 3 m, left eye - counting finger at 1 m distance, left eye oculomotor nerve palsy was present. MRI showed large extra-axial lesion involving left parasellar, medial temporal and basifrontal region measuring 5.5 cm × 5.5 cm × 6.9 cm in size. It was hypointense on T1 and heterogeneous on T2 with mass effect suggesting recurrence of the tumor [Figure 3]. He underwent reexploration, intraoperatively large extra-axial tumor with both cystic and solid component noted and subtotal excision of the tumor was done.
|Figure 3: Two-year postoperative magnetic resonance imaging image showing intensely enhancing lesion t the same site with multiple nonenhancing hypointense areas within it|
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Postoperative histology was similar to that described with first excision. Postoperative radiotherapy was given to residual disease on a linear accelerator by three-dimensional radiotherapy 2 Gy/fraction to a total dose of 54 Gy.
| > Discussion|| |
Schwannomas arise from Schwann cells of the myelin sheath of the peripheral nerve. Schwannomas constitute 7% of all intracranial neoplasms.  These may be sporadic or hereditary. Sporadic schwannomas are usually unilateral and common in the fourth or fifth decade of life. Hereditary schwannomas usually develop in second or third decade of life. These tumors are usually well circumscribed, grow in an expansible fashion, displacing the adjacent structures rather than invading them.
The majority of schwannomas arise from cranial nerve VIII (CN VIII) (vestibulocochlear nerve) and less commonly from CN V (trigeminal nerve), other CNs involvement are very rare. Schwannomas of the oculomotor nerve are extrememly rare. Celli et al.; divided oculomotor nerve schwannomas into three groups; cisternal, cisternocavernous and cavernous lesions.  This classification based on the preferred extension of these tumors. Oculomotor nerve schwannomas are most often in the interpeduncular cistern and less often in the cavernous sinus or orbit.
In our literature review we found that approximately 33 cases of well-documented oculomotor nerve schwannomas are reported in the literature, of which 12 cases are larger than 2.5 cm in diameter and largest measuring 5.5 cm in diameter.  Now we are reporting the case of oculomotor nerve schwannoma measuring 6.9 cm in diameter and will be the largest case in the literature to document till date.
Duration of symptoms before diagnosis are typically shorter than for other group of schwannomas, averaging 9-13 months. Most common presenting symptoms are diplopia and headache, other symptoms include visual loss due to compression of the optic nerve. 
Differential diagnosis of oculomotor schwannoma would include, parasellar or sellar lesions involving cavernous sinus, like meningioma which appears homogenous, hyperdense with hyperostosis of adjacent bones on plain computed tomography (CT) with an intense uniform enhancement contrast-enhanced CT and may calcify (25%). On MRI the lesion is isointense on T1-weighted, hyperintense on T2-weighted and will show rapid enhancement, with enhancing dural tail on contrast administration or pituitary macroadenoma, with lateral extension into cavernous sinus showing mixed signal intensity with uniform enhancement on MRI and is associated with enlarged sella turcica, supra-sellar extension, and diaphragmatic constriction.
Occulomotor schwannoma is difficult to differential from cisternal trochlear or trigeminal Schwannoma. Partially thrombosed aneurysm which will show variable signal on T1-weighted and T2-weighted sequences due to blood products in different stages of clot evolution.
Lymphoma and metastasis often involve adjacent bone with replacement of fatty bone marrow, with soft tissue of decreased signal intensity. Lymphoma often also shows leptomeningeal spread.
Para-midline chordomas are rare and are markedly hyperintense on T2-weighted sequences. 
Morphology and IHC
The histopathology showed characteristic features of the tumor with Antoni A and Antoni B areas. Nuclear palisading and verrcoy bodies were identified. There was mild cellular pleomorphism however mitosis was not seen. Immunohistochemistry with S-100 showed intense positivity within the tumor cells, and Ki-67 index was <1%.
These rare tumors are many options in their management. Very small lesions detected incidentally can be observed, symptomatic lesions can be managed with surgery or radiation therapy. A very high-incidence of complete oculomotor nerve palsy was reported in the literature after radical surgery, hence, a near total excision followed by radiotherapy provides a safer alternative compared to radical surgery. 
| > References|| |
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[Figure 1], [Figure 2], [Figure 3]