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.
