An atypical case of intracerebral schwannoma

We report a case of intracerebral cystic schwannoma in the temporal fossa manifested as a gradually worsening headache in a 49-years-old woman. Computed Tomography (CT) and magnetic resonance imaging (MRI) showed a left temporal partly cystic, partly solid mass. The preoperative diagnosis was astrocytoma or glioblastoma multiforme (GBM), but microscopic examination of the mass showed the characteristic pattern with cellular Antony A component. Immunohistochemically, the tumor was positive for S-100 protein. These findings are consistent with a schwannoma. Intracerebral schwannomas not related to cranial nerves are rare and most reported cases involved young patients.


Introduction
Intracranial schwannomas account for 8% of central nervous system tumors [1]. Most of these schwannomas arise from the vestibular portion of the VIIIth cranial nerve and less commonly, with descending order of frequency, from the Vth, IXth, Xth, and VIIth cranial nervesn [2], intraparenchymal schwannomas not related to cranial nerves are very rare, it represent less than 1%. To our knowledge, about 70 cases have been reported so far since the first case reported by Gibson et al in 1966 [3,4].

Discussion
Intracranial schwannomas account for 8% of central nervous system tumors [1]. Most of these schwannomas arise from the vestibular portion of the VIIIth cranial nerve. Intraparenchymal schwannomas not related to cranial nerves are very rare, it represent less than 1%. To our knowledge, about 70 cases have been reported so far.
Intraparenchymal schwannomas are located in both supratentorial and infratentorial areas; 63% and 37% respectively. The frontal and temporal lobes are the most common reported sites to be involved.
They were reported to originate from the ventricular and periventricular structures. They have also been described in the cerebellar hemispheres,vermis and brain stem [4,5].
Unlike vestibular schwannomas, the intraparenchymal schwannomas exhibit slight male predominance or even no female: male predominance. However Sharma et al reported a significant male to female ratio (M: F 3:1). Furthermore, the majority of cases have occurred in children and young adults, with average ages at presentation less than 21 years, unlike the vestibular schwannomas which usually occur in 5th decade unless associated with neurofibromatosis [6,7].
The characteristic features of intraparenchymal schwannomas include calcification, cysts formation, peritumoral edema, gliosis and a solid enhancing component. A variety of contrast enhancement patterns were described, including those of a cyst with a mural nodule and peripheral enhancement [7]. According to Y. Haga et al in a review of 30 cases, calcification was found in 17%, cyst formation was found in 27%, and surrounding edema was found in 53% of the tumors. Khoo HM et al reported that calcification was noted in 29%, cyst formation in 68 % and peritumoral edema in 87.5% of the cases. These characteristics appear to be more Page number not for citation purposes 3 frequent in intracerebral schwannomas than in acoustic neurinomas and peripheral schwannomas [4].
However these findings are not specific and may be seen in other primary CNS tumors. Preoperative diagnosis is difficult. In fact, the preoperative diagnosis of our case was astrocytoma or GBM, and the final diagnosis of schwannoma was based on histological and immunochemistry examinations. In CT, these tumors show an isoattenuated or low-attenuation contrast-enhancing mass associated with a cystformation. The MRI characteristics are variable but usually they demonstrate a hypointense and hyperintense signal intensity on T1-and T2-weighted images, respectively. The salient radiological feature in the reported cases was a very frequent cystic component [5,8,9].
What make the presented case unique or unusual compared to the reviewed cases, is that it lacks calcification and peritumoral edema.
The age also not typical, it is 49 years old which is much older than schwannoma [13]. Also Singh RVet al had reported a case of malignant cerebellar schwannoma [14].

Conclusion
The intracerebral schwannoma are almost benign tumors with very rare incidence. It may resemble the astrocytoma or GBM. The treatment of choice for these tumors is total excision with complete relief of clinical symptoms and signs mostly achieved.

Competing interests
The authors declare no competing interest.

Authors' contributions
Author contributions to the manuscript preparation include the following: conception and design: Zakzouk. Acquisition of data: Albatly. Analysis and interpretation of data: Alhaidey