Supratentorial convexity schwannoma unrelated to cranial nerves: Case report and review of the literature
- Department of Neurosurgery, Osaka Police Hospital, Tennoji, Osaka, Japan.
Department of Neurosurgery, Osaka Police Hospital, Tennoji, Osaka, Japan.
DOI:10.25259/SNI_193_2020Copyright: © 2020 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Daisuke Wajima, Shuta Aketa, Taiji Yonezawa. Supratentorial convexity schwannoma unrelated to cranial nerves: Case report and review of the literature. 06-Jun-2020;11:143
How to cite this URL: Daisuke Wajima, Shuta Aketa, Taiji Yonezawa. Supratentorial convexity schwannoma unrelated to cranial nerves: Case report and review of the literature. 06-Jun-2020;11:143. Available from: https://surgicalneurologyint.com/surgicalint-articles/10071/
Background: Intracranial schwannoma not related to cranial nerves is rare entity, and difficult to be diagnosed preoperatively. Here, we experienced a case of convexity schwannoma mimicking convexity meningioma, and discuss about the characteristics of such cases based on the past published reports.
Case Description: A 48-year-old man presented with a sudden onset of seizures. Brain magnetic resonance image (MRI) revealed a small mass lesion in the peripheral aspect of the right parieto-frontal lobe. The mass was isointense on T1-weighted and hyperintense on T2-weighted MRI, with homogenous enhancement after contrast medium administration. After the feeder embolization on the previous day, removal of the tumor was performed. The tumor revealed a well-demarcated, firm, spherical tumor beyond, and beneath the dura and was relatively easy to be separated from the brain. Histologically, the tumor was observed to be in subarachnoid space extending to outer space of dura-mater, intimately attached to the pia mater. The histological diagnosis was schwannoma.
Conclusion: In our case, MRI findings are similar to convexity meningioma; however, the pathological diagnosis was schwannoma. Cerebral convexity is an extremely rare location for schwannoma. We emphasize that schwannoma, not related to cranial nerves, may arise in the subdural convexity space.
Keywords: Convexity schwannoma, Unrelated cranial nerve origin, Review
The majority of intracranial schwannomas arises from the cranial nerves and usually occurs in the middle decades of life. Intracranial schwannoma not associated with cranial nerves is infrequent and usually involves in neurofibromatosis, and occurs among children or young adults.[
A 48-year-old man experienced a sudden onset of seizures in his left lower limb. He had never previously experienced such an episode. Gadolinium-enhanced MRI (Gd-MRI) revealed a small, homogenous-enhancing mass in the peripheral aspect of the right parieto-frontal lobe. The patient was referred to our hospital for further evaluation. The results of the physical examination performed at the time of admission were unremarkable. No cutaneous stigmata of neurofibromatosis Type I was observed. A neurological examination revealed no significant findings.
The lesion appeared as a well-defined, isosignal intensity area on T1-weighted MRI [
Preoperative magnetic resonance images (MRI). Preoperative MRI showed right frontal mass lesion. The lesion was isointense in T1-weighted MRI (a), hyperintense in T2-weighted MRI (b), hyperintense in fluid attenuation inversion recovery image (c), and homogenous enhanced with gadolinium intravenous injection (d: Axial image, e: Coronal image, and f: Sagittal image).
Digital subtraction findings (DSA). Preoperative DSA showed some feeding arteries (right middle cerebral artery branch [Right carotid artery angiography (Rt CAG)], a: Axial view, b: Lateral view), right anterior cerebral artery branch (Lt CAG, c: Axial view, d: Lateral view), and right middle meningeal artery (MMA) branch (Rt external CAG, e: Axial view, f: lateral view). Preoperative feeder embolization targeted to right MMA branch was performed (Rt external CAG, g: Axial view, h: Lateral view).
Our preoperative diagnosis was an extra-axial tumor, such as convexity meningioma or other tumors. A whole-body evaluation revealed no evidence of malignancy. The patient underwent a parietal craniotomy, with total resection of the tumor. During surgery, tumoral invasion beyond the dura mater was observed [
Intraoperative findings and postoperative MRI findings. During surgery, tumoral invasion beyond the dura mater was observed (a). When the dura was opened, a well-demarcated, firm, spherical tumor was observed beneath the arachnoid membrane. The tumor was elastic, hard, grayish in color, and loosely adherent to but separable from the dura mater (b). The tumor was totally removed piece by piece, with the adjacent brain tissue and dura (c). Postoperative MRI showed the total removal of the tumor (d: Axial view, e: Coronal view, f: sagittal view).
In light-microscopic assessments, the tumor was composed predominantly of Antoni Type A, and intermingled with Antoni Type B [
Histology findings. Compact bundles of thin, elongated, finely fibrillated cells, which tend to exhibit nuclear palisading (Antoni Type A) and which are intermingled with a looser pattern of Antoni Type B, can be observed. The adjacent cortex contained no tumor cells (a: hematoxylin and eosin (HE); original magnification, ×10). Immunohistochemical staining was positive for S-100 protein (b) but negative for glial fibrillary acidic protein (GFAP), cluster of differentiation (CD) 34, epithelial membrane antigen (EMA) (c), signal transducer and activator of transcription 6 (STAT 6) (d), progesterone receptor (PgR), and synaptophysin. The histopathological diagnosis was schwannoma. The tumor was observed to be in the subarachnoid space extending to the outer space of dura-mater, intimately attached to the pia mater (e: HE staining, f: Synaptophysin immunostaining).
Intracranial schwannoma are benign tumors that typically arise from the Schwann cells en-sheathing the axons beginning at the point of their exit from the pia mater. They usually develop among middle-age adults. Intracranial schwannomas comprise 6 to 8% of intracranial tumors.[
Intracranial schwannomas not related to cranial nerves are relatively rare; 74 cases have been reported.[
It is reasonable to consider the possibility that intracranial schwannomas not related to cranial nerves may develop from ectopic Schwann cells, because there are no Schwann cells in the central nervous system. Proposed hypotheses include: (1) the presence of Schwann cells in the autonomic nerves of the subarachnoid vessels, (2) the conversion of pial cells into Schwann cells, and (3) the presence of sensory nerves in the meninges of the convexity.
Although several hypotheses have been proposed to explain the origin of ectopic Schwann cells within the central nervous system, the histological origin of these tumors remains controversial. Proposed hypotheses include:
Schwann cell hyperplasia
Riggs and Clary proposed Schwann cell hyperplasia as the origin of intracranial neurinomas;[
The term “Schwannosis” was introduced by Russell and Rubinstein,[
Reactive changes after injury
Nelson and Rennels[
The possible differentiation of multipotent mesenchymal cell into Schwann cells (Neural crest origin)
Feigin and Ogata[
In our case, the tumor was present not within the brain parenchyma but in the subarachnoid space, extending to epidural space. It is possible that schwannomas could arise from small nerves in the subarachnoid space or the leptomeninges. Although several cases of schwannomas attached to the dura have been reported[
The imaging findings in our case were similar to convexity meningioma; however, there were no evident findings of “dural tail sign,” but the enhanced lesion extending along the meningeal or subarachnoid space; this location for schwannomas is exceedingly rare.
The differential diagnosis includes subdural, epidural, or leptomeningeal nodular brain metastasis, meningioma, glioma, and some granulomatous lesions (such as tuberculoma, fungal infections, and parasitic infections) when a well-demarcated spherical lesion associated with ring enhancement is observed adjacent to the cerebral convexity.
These lesions are uncommon, except for meningiomas, gliomas, and metastases.
We have reported on a middle-age man with a schwannoma located in the subarachnoid space and have presented computed tomography and MRI findings. Although there was no diagnostic clue indicating a convexity schwannoma (because of the rarity and nonspecific imaging features of such tumors), it should be recognized that schwannomas may arise in such rare locations as the subarachnoid space.
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