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Neurology India, Vol. 59, No. 5, September-October, 2011, pp. 756-760 Case Report Posterior fossa vermian cystic schwannoma mimicking as pilocytic astrocytoma: A case report and literature review Alok Umredkar1, Sunil Kumar Gupta1, Bishan Radotra2 1 Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India PMID: 22019665 DOI: 10.4103/0028-3886.86555 Keywords: Cerebellar tumor, intraparenchymal schwannoma, schwannoma vermian tumor Introduction 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. Case Report 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. Discussion 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
Copyright 2011 - Neurology India The following images related to this document are available:Photo images[ni11225f1.jpg] [ni11225.jpg] [ni11225t1.jpg] [ni11225f2.jpg] |
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