Radiological findings of intracranial subfrontal schwannoma: A case report

Abstract

We report a case of intracranial subfrontal schwannoma. A 27-years-old male suffered from a headache and visual disturbance. Neurological examination revealed left-sided anosmia and choked discs bilaterally. The patient had no pigmentation of von Recklinghausen's disease. Pre-contrast computed tomography (CT) showed a low-density mass about 8 cm in diameter in the left frontal region. Axial T2-weighted magnetic resonance imaging (MRI) revealed a hyperintensity mass in left anterior cranial fossa, with a deflecting falx to the right, and peritumoral cerebrospinal fluid collection and minimum surrounding edema. Sagittal T1-weighted MRI with Gd-DTPA enhancement showed a heterogenously enhanced mass without dural tail. No lesions were noted in the nasal cavity. The tumor was totally resected. Histological examination revealed schwannoma. Among the reported 14 cases of subfrontal schwannomas, only 7 were fully located in the intracranial cavity without any relation to von Recklinghausen's disease. Most of them were preoperatively diagnosed as olfactory groove meningioma, since it is the most common tumor in the anterior cranial fossa. We reviewed radiological images of previously reported cases and our own, and found some valuable findings to diagnose intracranial subfrontal schwannomas. Anterior floor changes on X-ray films and tumor stains on cerebral angiograms were rarely noted. CT showed low or iso-density on pre-contrast scans and high-density on post-contrast scans. MRI demonstrated hypointensity on T1-weighted image (WI) and hyperintensity on T2 WI. Gd-DTPA enhanced the tumor heterogenously rather than homogenously. No dural tail signs were seen. The angle between the tumor and anterior cranial base was acute. Some of these findings resemble those of acoustic neurinomas. Moreover, intracranial subfrontal schwannomas grew asymmetrically unlike olfactory groove meningiomas. To make differential diagnosis between intracranial subfrontal schwannoma and olfactory groove meningioma, we emphasize: 1) subfrontal schwannomas occurred at a relatively younger age; 2) radiological findings, especially no dural tail sign, an acute angle between the tumor and the anterior cranial base, asymmetrical growth, and absence of tumor stain, are important, and; 3) we should keep in mind that schwannoma grows even in the frontal base.