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Table of Contents    
Year : 2011  |  Volume : 59  |  Issue : 5  |  Page : 756-760

Posterior fossa vermian cystic schwannoma mimicking as pilocytic astrocytoma: A case report and literature review

1 Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India
2 Department of Histopathology, Postgraduate Institute of Medical Education and Research, Chandigarh, India

Date of Submission18-May-2011
Date of Decision27-May-2011
Date of Acceptance28-May-2011
Date of Web Publication22-Oct-2011

Correspondence Address:
Alok Umredkar
Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0028-3886.86555

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Intraparenchymal schwannomas are rare and most of the reported cases are in supratentorial region with frontal lobe being most common. Infratentorial location is very rare. We report a posterior fossa midline large cystic schwannoma with mural nodule mimicking as pilocytic astrocytoma. The pathogenesis and neuroradiological findings of intraparenchymal schwannomas are discussed with review of the related literature.

Keywords: Cerebellar tumor, intraparenchymal schwannoma, schwannoma vermian tumor

How to cite this article:
Umredkar A, Gupta SK, Radotra B. Posterior fossa vermian cystic schwannoma mimicking as pilocytic astrocytoma: A case report and literature review. Neurol India 2011;59:756-60

How to cite this URL:
Umredkar A, Gupta SK, Radotra B. Posterior fossa vermian cystic schwannoma mimicking as pilocytic astrocytoma: A case report and literature review. Neurol India [serial online] 2011 [cited 2021 Dec 6];59:756-60. Available from:

  Introduction Top

Schwannomas account for approximately 8% of all intracranial tumors, predominantly arising from the vestibular portion of the VIII th cranial nerve and less commonly from the V th , IX th , X th , and VII th cranial nerves. [1] While, schwannomas arising from other cranial nerves are rare and usually associated with Von Recklinghausen's disease, [2] intracranial schwannomas not arising from cranial nerves are extremely rare. [1] Most of the 70 reported cases of intraparenchymal schwannomas were supratentorial in location, either in the cerebral hemispheres or lateral ventricles. [1],[2],[3] Of the 26 reported cases with infratentorial location: 11 were in cerebellum and 6 were in vermis, and 9 were in brain stem [Table 1]. [3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16] All cases were benign except 2 malignant cases. We report a rare verminan cystic schwannoma which was mistake for a cystic glial tumor.
Table 1: Cases with cerebellar/vermian schwannoma during the study

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  Case Report Top

A 35-year-old woman presented with a 6-month history of progressive headaches, vomiting and gait ataxia. Neurological examination performed at admission showed papillaedema and bilateral cerebellar signs and gait ataxia. No cutaneous stigmata of neurofibromatosis Type 1 was observed. Computerized tomography (CT) scans of head revealed a large, cystic tumor in midline posterior fossa (vermian location), with obstructive hydrocephalous. Magnetic resonance imaging (MRI) of brain revealed a large, cystic tumor which was hypointense on T1-weighted [Figure 1]a and hyperintense on T2-weighted [Figure 1]b sequence, with solid enhancing nodule in inferior wall of cyst blocking the outlet of fourth ventricle [Figure 1]c and d. The initial diagnosis included primary intracranial tumor, including pilocytic astrocytoma, haemangioblastoma, and metastasis. She underwent midline suboccipital craniotomy with gross total resection of the tumor. Pale xanthochromic clear fluid was aspirated from the tumor. The cyst wall was then gently dissected off the cerebellar surface and completely excised. The cyst was found to be free from cranial nerves or blood vessels. The solid component was soft, suckable, and vascular in inferior part of cyst wall without attachments to any cranial nerve and blocking the fourth ventricular outlet causing obstructive hydrocephalous. Histopathological examination revealed schwannoma, and the tumor was composed of compact interlacing fascicles of spindle cells, characterized by elongated, hyperchromatic, and irregular nuclei, and occasional intranuclear inclusions, with scattered foci of nuclear palisading and hyalinised blood vessels [Figure 2]a. Tumor cells were reactive for S100 protein, neuron specific enolase (NSE) and vimentin and nonreactive for epithelial membrane antigen (EMA), glial fibrillary acidic protein (GFAP) and synaptophysin. The postoperative course was uneventful, and the patient was discharged on fourth post-operative day without neurological deficits. Follow-up MRI performed one year post-surgery showed no evidence of residual tumor [Figure 2]b-d. Patient remains asymptomatic at 2-year follow-up.
Figure 1: (a) T1 weighted magnetic resonance imaging scan of brain showing cystic hypoinense tumor with solid nodule isointense to cortex at periphery. (b) Magnetic resonance imaging of brain showing same cystic tumor hyperinsense on T 2 weighted scan with hypointense nodule. (c) Magnetic resonance imaging of brain showing dense contrast enhancement of solid nodule after gadolinium. (d) Contrast Magnetic resonance imaging of brain showing enhancing solid part of tumor at outlet of fourth ventricle

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Figure 2: (a) Photomicrograph of tissue specimen showing a schwannoma, spindle cell tumour composed of hypercellular area (Antoni A) with multiple hyalinizedd blood vessels. (hematoxylin and eosin; original magnification, ×100). (b) Contrast Magnetic resonance imaging of brain scan showing total excision of tumor. (c) Contrast Magnetic resonance imaging scan of brain showing total excision of solid nodule of shwannoma (d) Contrast sagital Magnetic resonance imaging scan of brain showing no residue or recurrence of schwannoma at 1 year post operative period

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  Discussion Top

There was no specific age predilection in the 17 published cases of intracerebellar schwannomas and 8 were males [Table 1]. [3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16] In the majority of cases, the tumor was located in the vermis, extending to either cerebellar hemispheres. In all the patients tumors were treated by total excision. The postoperative outcome and long-term follow-up were good in the majority of the reported cases except in the two patients with malignant tumors. [3],[12] As Schwann cells are normally not present in the cerebellar parenchyma, it is difficult to explain the origin of intracranial parenchymal schwannomas. Schwann cells have been detected around arteries in the subarachnoid space and within the periphery of the brain along the perivascular nerve plexus. [1] Several hypotheses have been proposed regarding the possible origin of schwannoma unrelated to cranial nerves. [17] These include possible origin from Schwann cells in perivascular plexuses, [18] conversion of pial cells to Schwann cells, [17] origin from misplaced myelinated nerve fibres, [19] from displaced neural crest cells in the developing nervous system, [20] or origin from multipotential mesenchymal cells. [21] Redekop and Elisevich proposed the theory of distorted embryogenesis. [22] All these theories can broadly be grouped under two categories: Developmental and non-developmental. [1] According to the developmental theory, aberrant Schwann cells in the brain parenchyma may occur due to the transformation of the mesenchymal pial cells or from displaced neural crest cells that form the foci of Schwann cells. [19] Non-developmental theories base their assumption on the fact that Schwann cells are present within the perivascular nerve plexi and large arteries in the subarachnoid spaces, although the existence of these structures deep in the brain parenchyma is doubted. [18] However, Schwann cells are clearly present in the adrenergic nerve fibres innervating the cerebral arterioles. These nerve plexi are common in tela choroidea, which may explain their predilection for periventricular location. [1] In our patient, we also correlate origin of schwannoma to these Schwann cells in adrenergic nerves supplying choroid plexus of fourth ventricle.

The differential diagnosis of an intracerebellar cystic schwannoma in middle age includes: pilocytic astrocytoma, hemangioblastoma, medulloblastoma, and mestastasis. The specimens should be examined using immunohistochemistry to make a correct diagnosis. [1],[3] Microscopic differential diagnosis includes fibroblastic meningioma and solitary fibrous tumor (Antoni type A predominant schwannoma), and pilocytic/pilomyxoid astrocytoma (Antoni type B predominant schwannoma). It is sometimes very difficult to differentiate between these neoplasms based on the histological examination alone, as there is an overlap in the histological features. Thus, either immunohistochemical or electron microscopic examination is crucial for the differential diagnosis. [23] In our patient, beside typical Antoni A and Antoni B areas, tumor cells were reactive for S100 protein, neuron specific enolase (NSE) and vimentin and negative for GFAP, supporting diagnosis of schwannoma.

The neuroradiological characteristics of intracerebellar schwannoma include: High frequency of calcifications, cystic formations, peritumoral edema, and angiographical vascularization. [1],[17] On CT, the tumors present as isodense or hypodense intra-parenchymal lesions either in cerebellar hemisphere or midline vermian region. They show uniform contrast enhancement and often have a cystic component. MRI characteristics are variable, with T1 isointensity and hypointensity and mixed T2 isointensity and hyperintensity. [1],[3],[17] Microcysts and edema are common with intracerebellar schwannomas. However, our patient is atypical and has one large cystic wall with solid mural component in inferior wall which mimics pilocytic astrocytoma.

Surgical treatment includes gross total excision. As most of these tumours are benign, no adjuvant therapy is needed. No recurrences were recorded after total excision. Few cases of malignant schwannoma were reported in which radiotherapy was given. [3],[12] In conclusion, intracerebellar schwannoma is a rare, benign neoplasm. It is usually located near midline adjacent to a vermis. Cystic nature of tumor may be confused with pilocytic astrocytoma or haemangioblastoma. These tumors cannot be preoperatively differentiated from other parenchymal tumors. Surgical excision is curative and the long term prognosis is good.

  References Top

1.Menkü A, Oktem IS, Kontaº O, Akdemir H. Atypical intracerebral schwannoma mimicking glial tumor: Case report. Turk Neurosurg 2009;19:82-5.  Back to cited text no. 1
2.Doi E, Ozaki F, Yabumoto M, Moriwaki H, Hayashi S, Komai N. Multiple malignant intracerebral schwannomas in von Recklinghausen's disease-report of a case. No Shinkei Geka [Article in Japanese] 1983;11:93-8.  Back to cited text no. 2
3.Maiuri F, Colella G, D'Acunzi G, De Caro Mdel B. Malignant intracerebellar schwannoma. J Neurooncol 2004;66:191-5.  Back to cited text no. 3
4.Komminoth R, Sokic P, Florange W, Komminoth J, Hartleyb H. Intracerebellar schwannoma. Neurochirurgie 1977;23:81-8.  Back to cited text no. 4
5.Kuhn JR, Neely JG, Pollay M. Cystic cerebellar schwannoma. Otolaryngol Head Neck Surg 1985;90:570-2.  Back to cited text no. 5
6.Sarkar C, Mehta VS, Roy S. Intracerebellar schwannoma. Case report. J Neurosurg 1987;67:120-3.  Back to cited text no. 6
7.Schwartz AM, Sotrel A. Intracerebral and intracerebellar neurilemoma. South Med J 1988;81:385-8.  Back to cited text no. 7
8.Benazza A, Houtteville JP, Chapon F, Khouri S, Hubert P. Intracerebellar schwannoma. Apropos of a case. Review of the literature. Neurochirurgie 1989;35:246-51.  Back to cited text no. 8
9.Tran-Dihn HD, Soo YS, O'Neil P, Chaseling R. Cystic cerebellar schwannoma: Case report. Neurosurgery 1991;29:296-300.  Back to cited text no. 9
10.Sharma MC, Newton G. Schwannoma of medulla oblongata. Br J Neurosurg 1993;7:427-9.  Back to cited text no. 10
11.Casadei GP, Komori T, Scheithauer BW, Miller GM, Parisi JE, Kelly PJ. Intracranial parenchymal schwannoma. A clinicopathological and neuroimaging study of nine cases. J Neurosurg 1993;79:217-22.  Back to cited text no. 11
12.Sing RV, Suys S, Campbell DA, Broome JC. Malignant schwannoma of the cerebellum: Case report. Surg Neurol 1993;39:128-32.  Back to cited text no. 12
13.Ranjan A, Chacko G, Chandi SM. Intracerebellar melanotic schwannoma: A case report. Br J Neurosurg 1995;9:687-9.  Back to cited text no. 13
14.Sharma MC, Karak AK, Gaikwad SB, Mahapatra AK, Mehta VS, Sudha K. Intracranial intraparenchymal schwannomas: A series of eight cases. J Neurol Neurosurg Psychiatr 1996;60:200-3.  Back to cited text no. 14
15.Tsuiki H, Kuratsu J, Ishimaru Y, Nakahara T, Kishida K, Takamaru M, et al. Intracranial intraparenchymal schwannoma: Report of three cases. Acta Neurochir (Wien) 1997;139:756-60.  Back to cited text no. 15
16.Bhatjiwale M, Gupta S. Midline cerebellar cystic schwannoma: A case report. Neurol India 1999;47:127-9.  Back to cited text no. 16
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17.Ozawa N, Nakayama K, Ohata K, Okamura T, Inoue Y. Tentorial schwannoma: A case report. Br J Radiol 2003;76:421-4.  Back to cited text no. 17
18.Riggs HE, Clary WU. A case of intramedullary sheath cell tumor of the spinal cord. Consideration of vascular nerves as a source of origin. J Neuropathol Exp Neurol 1957;16:332-6.  Back to cited text no. 18
19.Prakash B, Roy S, Tandon PN. Schwannoma of the brain stem; Case report. J Neurosurg 1980;53:121-3.  Back to cited text no. 19
20.Ramamurthi B, Anguili VC, Iyer CG. A case of intramedullary neurinoma. J Neurosurg Psychiatry 1958;21:92-4.  Back to cited text no. 20
21.Fegin I, Ogata J. Schwann cells and peripheral myelin within human central nervous tissue: The mesenchymal character of schwann cells. J Neuropathol Exp Neurol 1971;30:603-12.  Back to cited text no. 21
22.Redekop G, Elisevich K. Fourth ventricular schwannoma. J Neurosurg 1990;73:771-81.  Back to cited text no. 22
23.Takei H, Schmiege L, Buckleair L, Goodman JC, Powell SZ. Intracerebral schwannoma clinically and radiologically mimicking meningioma. Pathol Int 2005;55:514-9.  Back to cited text no. 23


  [Figure 1], [Figure 2]

  [Table 1]


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