British Journal of Radiology (2003) 76, 421-424
© 2003 British Institute of Radiology
doi: 10.1259/bjr/20106153
Tentorial schwannoma: a case report
N Ozawa, MD1,
K Nakayama, MD1,
K Ohata, MD2,
T Okamura, MD1 and
Y Inoue, MD1
Departments of Radiology and 2 Neurosurgery, Osaka City University Medical School, 1-5-7 Asahimachi Abeno-ku Osaka 545 8585 Japan
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Abstract
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A rare case of tentorial schwannoma in a 29-year-old male is described. The schwannoma was located within the leaves of the tentorium. MRI showed a wedge-shaped enhancing tumour. Exact nerve of origin of the tumour could not be identified. We speculate that the tumour arose from the tentorial branch of the trigeminal nerve. The literature concerning intracranial schwannoma unrelated to a major cranial nerve is reviewed.
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Introduction
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Intracranial schwannomas comprise approximately 8% of all intracranial tumours [1]. Schwannomas arise most commonly from the vestibular nerve and less frequently from the trigeminal nerve. Rarely they arise from the vagus or the glossopharyngeal nerves. Schwannomas arising unrelated to a major cranial nerve are extremely rare. We present a case of a cerebellar tentorial schwannoma. Probable histogenesis of the tumour and radiographic findings are discussed.
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Case report
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A 29-year-old man was admitted with a 5-year history of occasional mild headache. 3 months before admission he had transient diplopia which subsided spontaneously. There was no other symptom. Neurological examination was normal. No family history or cutaneous stigmata of von Recklinghausen's disease were found. CT scan revealed a well-defined isodense partly cystic mass without calcification in the right ambient cistern that displaced the midbrain medially. The mass was approximately 20 mm in diameter. The lesion showed heterogeneous enhancement after intravenous contrast injection (Figure 1
). MRI showed the mass to be of heterogeneous signal intensity. The solid portion of the mass was isointense to grey matter both on T1 weighted images and on T2 weighted images, and enhanced homogeneously after contrast administration. There was no significant peritumoural oedema (Figure 2a, b). Linear enhancement was observed in the tentorial edge, which was in continuity with the mass mimicking the so-called "dural tail" sign (Figure 2c, d). A contrast-enhanced sagittal T1 weighted image revealed an enhanced wedge-shaped tentorial edge adjacent to the mass (Figure 2d). Transpetrosal approach was adopted for surgery. The tumour was found within the two leaves of the tentorium. The tentorium was of normal texture and vascularity. The tumour was well encapsulated, soft and yellowish. The trochlear nerve was identified medial to the mass (Figure 3). No definite nerve could be identified in relationship to the tumour. Histological examination showed that the tumour had the characteristic appearance of a schwannoma, with bipolar spindle shaped cells and loose-textured area, which represented Antoni type A and Antoni type B cells. Pallisading of the cells was partially seen (Figure 4). There was no mitosis or necrosis.
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Figure 1. Axial contrast-enhanced CT scan at the level of the Pons reveals a heterogeneously enhanced mass approximately 20 mm in diameter at the right ambient cistern.
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Figure 2. Axial T1 weighted MRI at the level of the Pons. The mass is isointense to hypointense to brain on T1 weighted image (a). On T2 weighted image mixed signal intensity, composed of an isointense solid portion and a hyperintense cystic portion compared with brain was noted (b). The lesion enhances homogeneously after intravenous administration of contrast media (c). The midbrain is displaced medially and deformed. Wedge-shaped dural enhancement (arrow) which tapers backward is seen on the contrast-enhanced T1 weighted sagittal image (d).
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Figure 3. Schematic illustration of the cerebellar tentorial schwannoma (axial plane). The mass was located between the two leaves of the cerebellar tentorium, compressing and displacing the right trochlear nerve and midbrain.
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Figure 4. Photomicrograph of the surgical specimen, H&E, original magnification x 200. Photomicrograph of the surgical specimen shows long bipolar spindle cells with sporadic pallisading (a) and cells containing eosinophilic matrix (b), consistent with schwannoma.
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Post-operatively the patient had paresis of the right oculomotor, trochlear and trigeminal nerve. At follow-up after 2 months all cranial nerves improved, except for the right trochlear nerve palsy, which persisted.
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Discussion
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Schwannomas arising within the central nervous system unrelated to a major cranial nerve are extremely rare. Approximately 50 such schwannomas have been reported [2–16]. Most of the reported cases were located in the cerebral hemispheres and presented as an intra-axial tumour. About 14 cases have been documented as extra-axial schwannomas. Two of these reported schwannomas were attached to the falx [4, 5], one to the dura in the region of tuberculum sellae [6], one in the intrasellar region [7], one in the petroclival intradural region without attachment to dura and neural tissue [8] and the remainder in the subfrontal region [5, 9].
A variety of hypotheses have been proposed regarding the possible mode of origin of schwannoma unrelated to cranial nerves. These include possible origin from schwann cells in perivascular plexuses [10], conversion of pial cells to schwann cells [1], origin from misplaced myelinated nerve fibres [11] and from displaced neural crest cells in the developing nervous system [12], or origin from multipotential mesenchymal cells [13]. Redekop supported the theory of distorted embryogenesis [14].
In our case, it is possible that the origin of the schwannoma is from the normally-existing schwann cells in the tentorium. It is possible that the tumour could have arisen from the tentorial branches of the trigeminal nerve or from one of the multiple perivascular nerve fibrils.
CT and MRI findings were compatible with schwannoma, although the location of the tumour was unusual. Differential diagnosis of an enhancing and well-circumscribed mass in the region of the ambient cistern includes trochlear nerve schwannoma, cystic meningioma arising from the tentorial edge and exophytic glioma of the midbrain. Linear enhancement of the tentorium suggested that there was some anatomical relation between the tumour and the tentorium, but it was difficult to predict the precise tumour location before surgery. Retrospectively, the wedge-shaped tentorial enhancement adjacent to the tumour best demonstrated on the enhanced T1 weighted sagittal images seems to be a clue of the tumour location in the two leaves of the cerebellar tentorium.
Recently, two cases of schwannoma attached to the cerebellar tentorium have been reported in the neurosurgical journals. Oikawa et al [15] have described a 41-year-old female, in who MRI revealed an extra-axial mass mixed cystic and solid component in the left anteromedial cerebellar region. Jabbour et al [16] have reported a 9-year-old girl, in who MRI revealed a large infratentorial solid mass attached to the cerebellar tentorium with homogeneous enhancement. Tentorial dural tail sign was seen in both cases. In our case, tentorial dural tail sign was also observed. Tentorial schwannoma, although unusual in location, should be considered as differential diagnosis of a mixed cystic and solid mass with tentorial dural tail sign adjacent to the mass.
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Acknowledgments
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The authors thank for Professor Atul Goel, MD, in India for helpful valuable comments and editing of this manuscript.
Received for publication July 25, 2002.
Accepted for publication October 21, 2002.
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References
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Abstract
Introduction
