Olfactory Groove Schwannoma: A Case Report

We would like to report a case of a 71-year-old woman who presented to the neurosurgery clinic due to an incidentally discovered olfactory groove schwannoma. Magnetic resonance image of the brain was obtained ([Fig. 1A–C]). Due to the patient's advanced age and the benign imaging features of the lesion, monitoring was decided upon. However, growth of the lesion was noted on follow-up and gross total resection was done ([Fig. 1D]). Histopathology revealed schwannoma ([Fig. 2]). At the 1-year follow-up, the patient had right-sided anosmia.

Fig. 1 Coronal (A), sagittal (B), and axial (C) T1-weighted, gadolinium-enhanced, brain MR image demonstrating a well-circumscribed, homogenously enhancing, extra-axial, anterior cranial fossa lesion eroding the ethmoid bone. Coronal (D) T1-weighted, gadolinium-enhanced, brain MR image showing gross total resection of the tumor.

Fig. 2 Histopathologic examination revealed pauci-cellular and more cellular regions (A) composed of spindle cells, without marked nuclear atypia or increased mitotic activity, with ill-formed nuclear palisading (B), diffusely immune-positive for S-100 (C).

Olfactory groove schwannomas are rare, extra-axial, benign tumors. In contrast to other intracranial schwannomas, they frequently affect young males.[1] [2] Moreover, since the olfactory bulb is devoid of Schwann cells,[1] [3] their pathogenesis is unclear with several theories proposed: The developmental theories suggest mesenchymal pial cell transformation into Schwann cell or aberrant neural crest cell migration.[1] [2] [4] The nondevelopmental theory suggests origin from Schwann cells present in adjacent structures.[1] [2] [4] Finally, reactive Schwann cell formation from multipotential mesenchymal cells has also been proposed.[1]

Histopathologic findings pathognomonic for schwannoma include densely packed elongated cells with palisading nuclei (Antoni A pattern) alternating with less cellular regions (Antoni B pattern).[3] On immunohistochemistry, schwannomas stain was positive for S-100[3] and CD-57 (Leu-7)[2] [4] and negative for smooth muscle α-actin.[4] Management should be individualized, and includes observation, surgical resection, and radiosurgery.[3]

In conclusion, the pathogenesis of olfactory groove schwannomas remains unclear. They should be included in the differential diagnosis of anterior cranial fossa neoplasms.

Funding

None.

• References

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• 3 Carron JD, Singh RVP, Karakla DW, Silverberg M. Solitary schwannoma of the olfactory groove: case report and review of the literature. Skull Base 2002; 12 (03) 163-166
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