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LETTER TO EDITOR
Year : 2014  |  Volume : 62  |  Issue : 1  |  Page : 99-100

Sixth nerve schwannoma


1 Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
2 Department of Neuropathology, All India Institute of Medical Sciences, New Delhi, India

Date of Submission14-May-2013
Date of Decision15-May-2013
Date of Acceptance26-Jan-2014
Date of Web Publication7-Mar-2014

Correspondence Address:
Rajinder Kumar
Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.128355

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How to cite this article:
Kumar R, Kothiwala A, Ghosh R. Sixth nerve schwannoma. Neurol India 2014;62:99-100

How to cite this URL:
Kumar R, Kothiwala A, Ghosh R. Sixth nerve schwannoma. Neurol India [serial online] 2014 [cited 2019 Sep 16];62:99-100. Available from: http://www.neurologyindia.com/text.asp?2014/62/1/99/128355


Sir,

Schwannomas represent approximately 7-10% of all primary intracranial tumors. The most frequent are in eight and fifth cranial nerves. [1] Schwannoma arising from the sixth cranial nerve is exceedingly rare. Due to its close proximity to fifth and eight nerves and similar clinical and radiological findings, it is difficult to diagnose sixth nerve schwannoma preoperatively. [2],[3]

A 42-year-old male presented with a history of diplopia on the left lateral gaze and intermittent headache for 6 months. There was no family history suggestive of neurofibromatosis. Neurological examination revealed left 6 th nerve paralysis [Figure 1]a. Magnetic resonance imaging (MRI) brain revealed a left cerebellopontine angle lesion iso to hypointense on T1-WI [Figure 2]a hyperintense on T2-WI [Figure 2]b enhancing heterogeneously on contrast [Figure 2]c. The internal acoustic meatus was of normal size. A small enhancing component of the tumor was seen going toward the Dorello's canal [[Figure 2]c arrow head]. Patient underwent left retromastoid suboccipital craniotomy and gross total excision of tumor under intraoperative cranial nerve monitoring. The tumor was arising from 6 th cranial nerve. He had an uneventful recovery. At 3 months follow-up, the MRI brain was normal [Figure 2]d and sixth nerve paralysis improved to normal [Figure 1]b. Histopathological examination revealed a cellular tumor composed of spindle-shaped cells with oval-to-spindle nuclei and a moderate amount of cytoplasm. The tumor cells were arranged in palisading pattern and formed verocay bodies [Figure 3].
Figure 1: (a) Pre-operative and (b) post-operative clinical photograph

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Figure 2: (a) T1-WI, (b) T2-WI, (c) post contrast magnetic resonance imaging (MRI) and (d) post-operative MRI (arrow heads showing tumor entering Dorello's canal)

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Figure 3: Histopathological slide showing spindle-shaped cells arranged in palisading pattern with Verocay bodies

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All the cranial nerves except first and second have covering myelin sheath composed of Schwann cells and are potential sites for developing schwannoma. Most common location of intracranial schwannoma is in the cerebello-pontine angle where they arise from the vestibular division of the eighth nerve. Other common sites of origin are lower cranial nerves, fifth nerve and in the region of cavernous sinus. [1],[2],[4] First case of sixth nerve schwannoma was reported by Chen in 1981. [5] Tung has classified them into two types according to location. [6] Type 1 schwannomas are present in the cavernous sinus region and type 2 are present in prepontine cistern. In the absence of neurofibromatosis the isolated prepontine location is extremely rare. The exact site of origin is difficult to ascertain before surgery. However, this patient was diagnosed to be sixth nerve schwannoma before surgery. Isolated sixth nerve involvement in the absence of involvement of fifth, seventh and eight nerves, extension of tumor toward the Dorello's canal seen in 3-Tesla MRI, helped in diagnosis. However sixth nerve involvement as a presenting feature could be seen in clival chordoma and cavernous sinus lesions. [1],[6] Clinically and radiologically it may mimic vestibular schwannoma. However symptoms starting with diplopia due to sixth nerve involvement is the most important clinical feature to suspect the isolated sixth nerve involvement and tumor going anteriorly toward Dorello's canal [[Figure 2]b and c arrow head] is an important finding in favor of sixth nerve schwannoma.

The goal of the surgery is to preserve function and achieve complete excision. These tumors arise from nerve sheath of a fascicle, hence complete excision sparing the main nerve is possible. This patient had complete recovery of the 6 th nerve function at 3 months follow up. This fact emphasizes the importance of meticulous dissection and excision of the tumor. Hence excision of tumor in the accessible location is recommended.

 
  References Top

1.Sarma S, Sekhar LN, Schessel DA. Nonvestibular schwannomas of the brain: A 7-year experience. Neurosurgery 2002;50:437-48.  Back to cited text no. 1
    
2.Suetake K, Kurokawa Y, Uede T, Momota H, Hashi K. A case of abducens neurinoma mimicking acoustic neurinoma. Comput Med Imaging Graph 1998;22:257-61.  Back to cited text no. 2
    
3.Beppu T, Yoshida Y, Wada T, Arai H, Suzuki M, Kuroda K, et al. Trochlear and abducens nerve neurinomas accompanied by a cerebellopontine angle meningioma: Case report. Neurol Med Chir (Tokyo) 1997;37:416-21.  Back to cited text no. 3
    
4.Erlich SA, Tymianski M, Kiehl TR. Cellular schwannoma of the abducens nerve: Case report and review of the literature. Clin Neurol Neurosurg 2009;111:467-71.  Back to cited text no. 4
    
5.Chen BH. Neurinoma of the abducens nerve. Neurosurgery 1981;9:64-6.  Back to cited text no. 5
    
6.Tung H, Chen T, Weiss MH. Sixth nerve schwannomas. Report of two cases. J Neurosurg 1991;75:638-41.  Back to cited text no. 6
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]

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