Olfactory Groove Schwannoma: A Case Report and Literature Review

Introduction: Schwannomas are benign, slow-growing tumors which derive their name and origin from Schwann cells and occur most frequently in the cranial nerves. The optic and olfactory nerves, however, lack Schwann cells and so CN I or CNII schwannomas are therefore not possible. This case demonstrates an intra-axial schwannoma of the olfactory groove extending into the sinus cavity.

Clinical Case: A 56-year old male presented to our rhinology clinic for evaluation of a known intra-axial anterior skull base mass that had been present for at least five years and monitored clinically at an outside hospital. Surveillance MRI demonstrated an expansile mass approximately 2.1 cm × 1.4 cm in size centered over the cribriform plate with expansion into the ethmoid sinus ([Figs. 1] [2] [3] [4]). Given interval growth of the mass as compared with prior imaging, biopsy was performed in the operating room, with histopathologic evaluation demonstrating spindle cell proliferation. Cells were diffusely positive for S100, SOX10, and INI-1 and negative for SSTR2A on immunohistochemistry. According to these observations the mass was defined as a schwannoma, CNS WHO Grade I.

Discussion: Schwannomas of the anterior cranial fossa, and specifically of the olfactory groove, are exceedingly rare tumors, with less than 100 cases described in the literature. The pathogenesis of olfactory groove schwannoma is not fully known, though it is generally agreed upon that given the lack of Schwann cells of CNI, the olfactory bulb is not the nerve of origin. The most plausible sites of origin, rather, are the nearby structures whose myelin sheath is produced by Schwann cells. These include the dural branches off of the first division of the trigeminal nerve, the filia olfactoria (which connect olfactory bulb to olfactory epithelium and acquire Schwann cells 0.5 mm beyond the olfactory bulb), and the nervus terminalis. Less obvious hypotheses based in developmental pathogenesis suggest the growth of schwannoma from Schwann cells atypically present in the central nervous system (CNS) due to aberrant differentiation of neural crest cells or multipotent mesenchymal cells; these theories are more likely to explain intraparenchymal than extraparenchymal schwannomas. Definitive diagnosis consists of histopathologic evaluation revealing spindle cells in either Antoni A (palisading spindle cells) or Antoni B (loose myxoid stoma with small amount spindle cells) configuration; these cells stain strongly with S-100 on immunohistochemistry. Treatment consists of complete surgical excision. This patient underwent a uninarial endoscopic endonasal transcribiform approach for resection with a fascia button graft and nasoseptal flap for closure.

Conclusion: Olfactory groove schwannomas are benign, rare tumors often presenting nonspecifically, making them difficult to diagnose without tissue sample. They should be considered in the differential diagnosis of sinonasal masses with cribriform plate involvement.

Fig. 1 Sagittal CT image without contrast.

Fig. 2 Coronal CT image without contrast.

Fig. 3 Sagittal MRI image with contrast.

Fig. 4 Sagittal MRI image with contrast.

 

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No conflict of interest has been declared by the author(s).

Publication History

Article published online:
07 February 2025