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Pontine extension of a tentorial schwannoma without cranial nerve involvement: a case report
© D'Urso et al; licensee BioMed Central Ltd. 2011
Received: 9 July 2011
Accepted: 28 December 2011
Published: 28 December 2011
Intracranial schwannomas unrelated to the cranial nerves are uncommon. We report a new case of tentorial schwannoma unrelated to the cranial nerves, with extension into the pons. A literature review with discussion of the most relevant pathogenetic aspects is also performed.
A 42-year-old Caucasian man was admitted with right-sided paresthesias and weakness of his upper and lower extremities. The neurological examination revealed right hemiparesis and hemi-hypoesthesia. A brain magnetic resonance imaging scan revealed a cerebellopontine lesion, arising from the left free edge of the tentorium, and extending into his pons. A piecemeal removal was performed through a retrosigmoid approach. The lesion was not found to be associated with any cranial nerves. The histological examination revealed a schwannoma Antoni type A. His postoperative course was uneventful. At one year follow-up, the patient was neurologically intact and the magnetic resonance imaging of his brain performed at that time showed complete removal without signs of recurrence.
Tentorial schwannomas are rare clinical entities. Knowledge of their clinical, radiological and anatomical characteristics is very important for the correct diagnosis and management.
Schwannomas constitute about 8% of primary intracranial tumors and account for almost 80% to 90% of cerebellopontine angle tumors. Most cases are related to the eighth cranial nerve, and less commonly to other cranial nerves. Intracranial schwannomas not associated with cranial nerves are uncommon [1, 2]. To date, only 11 cases of intracranial schwannomas arising from the tentorium have been reported [1, 3–12].
We report a new case of a tentorial schwannoma unrelated to the cranial nerves, with extension into the pons. A literature review with the discussion of the most relevant pathogenetic aspects has also been performed.
Surgery was performed using a retrosigmoid approach. After retraction of the hemispheric cerebellar lobe, a yellowish extra-axial lesion of the cerebellopontine angle was discovered. The tumor was strongly attached to the superior surface and the free edge of the tentorium, extending into the pons parenchyma. An endocapsular piecemeal removal was performed by means of an ultrasonic aspirator; the lesion appeared friable and vascularized. The cranial nerve complexes V, VII, VIII, IX, × and XI were all identified and preserved, and the mass was not found to be associated with these cranial nerves. The intraparenchymal portion was carefully dissected by the brain stem. After dissection from the surrounding structures, the lesion was mobilized and its implantation on the left free edge and superior surface of the tentorium exposed and resected. After tumor removal, the IV cranial nerve was exposed in its arachnoid cistern. At the end of the procedure, coagulation and resection of the implantation were achieved.
His postoperative course was uneventful and our patient fully recovered from his preoperative deficits.
Summary of the reported cases of tentorial schwannoma
MRI dural tail
Schwannoma (Antoni A)
Dizziness, headache, vomiting, unsteadiness
MRI: no residual/recurrent tumor (12 months)
Truncal ataxia, unsteadiness
MRI: no residual/recurrent tumor (16 months)
Headache, transient diplopia.
Schwannoma (Antoni A and B)
IV cranial nerve deficit (2 months)
Headache, diplopia, nystagmus
MRI: no residual tumor
Dizziness, swallowing difficulty
Schwannoma (Antoni A)
Headache, neck pain, vomiting, unsteadiness; right facial paresis; right facial paresthesia; neurofibromatosis
Recovery, except for residual facial paresthesia (1 month)
Good (at 6 months)
MRI: small residual tumor
Transient global amnesia
MRI: residual tumor
Schwannoma (Antoni A & B)
stable residual tumor (24 months)
Paresthesia and weakness of the four extremities
Schwannoma (Antoni A)
MRI: no residual/recurrent tumor (12 months)
Typically, tentorial-based schwannomas appear on radiology as a heterogeneous enhancing cystic lesion, occasionally encased in the surrounding brain parenchyma, but without peritumoral edema; as in our case, a dural tail sign is often present .
Several surgical approaches have been reported to remove this kind of tumor (Table 1). In our case, we used a retrosigmoid approach. An alternative approach could be a subtemporal route, because of the tumor location in the middle incisural space. However, dealing with a left-sided lesion in a right-handed patient, we preferred a retrosigmoid approach to avoid a temporal venous infarction secondary to brain retraction, a complication reported as symptomatic in 2.6% to 13% of these approaches .
There are several hypotheses about the origin of intracranial schwannomas unrelated to the cranial nerves . Interestingly, some authors have suggested that these lesions could arise from Schwann cells normally present within the perivascular nerve plexuses surrounding arteries in the subarachnoid space, or from Schwann cells of meningeal branches of the trigeminal and anterior ethmoid nerves . The absence of cranial nerve deficits and the frequent presence of a unilateral headache strongly suggest a possible origin of the thin branches of the trigeminal ganglion or of the sensorial branches of the first division of the trigeminal nerve which supplies the tentorium. These branches were first described by Arnold in 1826 .
Although the absence of postoperative cranial nerves deficits has been advocated as proof that these lesions do not arise from cranial nerves, this observation has been questioned by some authors, since a lack of postoperative symptoms could be related to the compensative mechanism of ocular movements .
Tentorial schwannomas are rare clinical entities, but the knowledge of their clinical, radiological and anatomical characteristics is very important for a correct diagnosis and management.
Written informed consent was obtained from the patient for publication of this manuscript and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
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