Neurol India Home 

Year : 2004  |  Volume : 52  |  Issue : 2  |  Page : 261--262

Cystic olfactory groove schwannoma

SN Shenoy, A Raja 
 Department of Neurosurgery, Kasturba Medical College and Hospital, Manipal, India

Correspondence Address:
S N Shenoy
Department of Neurosurgery, Kasturba Medical College and Hospital, Manipal - 576119. Udupi


Intracranial schwannoma not related to cranial nerves are unusual and rarely found in the subfrontal region. We report a case of cystic olfactory groove schwannoma in a 55-year- old male, who presented with late onset seizure without raised intracranial pressure. The tumor was excised completely.

How to cite this article:
Shenoy S N, Raja A. Cystic olfactory groove schwannoma.Neurol India 2004;52:261-262

How to cite this URL:
Shenoy S N, Raja A. Cystic olfactory groove schwannoma. Neurol India [serial online] 2004 [cited 2021 Sep 27 ];52:261-262
Available from:

Full Text


Intracranial schwannomas not associated with cranial nerves account for less than 1% of surgically treated schwannomas of the central and peripheral nervous system.[1],[2] Subfrontal schwannomas are rare and less than 20 cases have been reported in the literature.[1],[2],[3],[4],[5] We report a case of cystic olfactory groove schwannoma and briefly review the literature.

 Case Report

A 55-year-old man had an episode of generalized seizures. There were no symptoms of raised intracranial pressure or focal neurological deficit. Neurological examination revealed preserved olfaction and no other abnormality. The T1-weighted magnetic resonance (MR) image revealed a well-defined hypointense lesion situated in the midline anterior cranial fossa, elevating and minimally compressing the frontal lobe. The lesion was homogenously hyperintense in the T2-weighted image and isointense in the flair images [Figure:1]. The Gadolinium injection caused a heterogeneous enhancement giving it a honeycomb appearance [Figure:2].

He underwent left fronto-temporal craniotomy and total excision of the tumor. The tumor was grayish, well-defined and contained multiple cysts filled with xanthochromic fluid. The intervening tissue was grayish, containing thin blood vessels. The tumor was attached to the dura just lateral to the left cribriform plate with a narrow pedicle. The ipsilateral olfactory bulb was flattened and markedly thinned out and could not be separated from the surrounding gliotic cortex. However, the contralateral olfactory tract was preserved. The histopathological features were suggestive of typical schwannoma. The tumor cells exhibited a strongly positive staining pattern for S-100 protein.


Schwannomas commonly arise from the nerve sheaths of the peripheral and the cranial nerves and represent approximately 8% of all intracranial tumors.[5] Even though schwannomas have been reported to originate from all the cranial nerves, except the optic nerve, most arise from the vestibular nerve.[5] Very few cases of intracranial schwannomas without a cranial nerve or dural attachment have been reported in the literature.[1],[2],[3],[4] The pathogenesis of these intracranial schwannomas is puzzling as the central nervous system is devoid of the Schwann cells.[1],[2] Various theories regarding the possible origin of these tumors are centered around developmental and non-developmental origins.[1],[2],[5] The developmental theories suggest either transformation of mesenchymal pial cells into ectodermal Schwann cells or migration of the neural crest cells within the substance of the central nervous system.[5] On the other hand, the proponents of the non-developmental theories postulate that intracranial schwannomas arise from Schwann cells normally present in the adjacent structures such as the perivascular nerve plexus and the meningeal branches of the trigeminal and anterior ethmoidal nerves innervating the anterior cranial fossa.[5] In our case, the tumor was arising from the basal dura at the site of olfactory bulb. The attachment of the tumor was very narrow, suggesting that the schwannoma might have originated from the small nerves in the basal dura matter.

About 50% of patients with subfrontal schwannomas are younger than 30 years with a 3:1 male predominance.[1],[6] The clinical manifestation varies from features of raised intracranial pressure to focal neurological deficits such as anosmia.[1],[4] These tumors vary from homogeneously enhancing solid lesions to sparsely enhancing cystic lesions as seen in our case.[1],[4],[6],[7] Radiologically, these lesions are often mistaken for olfactory groove meningiomas.[1],[3],[4],[6] The presence of hyperostosis and the dural tail sign suggest meningioma whereas bone erosion is more consistent with a schwannoma.3 Surgery remains the main therapeutic modality and due to the benign nature of the tumor, complete excision is associated with cure.


1Huang PP, Zagzag D, Benjamim V. Intracranial schwannoma presenting as a subfrontal tumour: Case report. Neurosurgery 1997;40:194-7.
2Goel A, Bhayani R, Nagpal RD. Unattached intracranial extra-axial schwannoma. Br J Neurosurg 1996;10:405-7.
3Amador AR, Santonja C, Del Pozo JM, Ortiz L. Olfactory schwannoma. Eur Radiol 2002;12:742-4.
4Praharaj SS, Vajramani GV, Santosh V, Shankar SK, Kolluri S. Solitary olfactory groove schwannoma: Case report with review of the literature. Clin Neurol Neurosurg 1999;101:26-8.
5Russell DS, Rubinstein LJ. Pathology of tumors of the nervous system. 5th (Ed). London: Arnold 1989:776-7.
6de Souza HL, Ramos AM, Ramos CC, Melo SP, Pereira HS, Madureira JF, et al. Olfactory groove schwannoma: Case report. Arq Neuropsiquiatr 2003;61:125-8.
7Tali ET, Yuh WT, Nguyen HD, Feng G, Koci TM, Jinkins JR, et al. Cystic acoustic schwannomas: MR characteristics. Am J Neuroradiol 1993;14:1241-7.