Combined Interhemispheric and Endoscopic Endonasal Resection of a Rare Olfactory Schwannoma with Preservation of Olfactory Function.

INTRODUCTION: Olfactory groove schwannomas (OGSs) are exceptionally rare intracranial tumors, with fewer than 80 cases reported. Their imaging features often mimic meningiomas or esthesioneuroblastomas, complicating preoperative diagnosis. Their origin remains debated due to the absence of Schwann cells in the olfactory nerve. RESEARCH QUESTION: To describe a rare case of olfactory groove schwannoma with ethmoidal extension, successfully treated through a combined interhemispheric and endoscopic endonasal approach, and to discuss its diagnostic and surgical implications in light of the current literature. Furthermore, to measure the respective olfactory function before and after surgery. MATERIAL AND METHODS: A 52-year-old man presented with transient visual disturbances, headache, lexical access difficulties, slight executive dysfunction with impaired inhibition, and anterograde verbal memory impairment. He had no olfactory complaints but olfactory testing revealed unilateral, left-sided anosmia. Preoperative MRI demonstrated a large left olfactory groove mass with solid-cystic components, bone erosion, and inferior ethmoidal extension. A combined transcranial interhemispheric and endoscopic endonasal approach was performed to achieve total resection and ensure skull base reconstruction. RESULTS: Gross total tumor removal was achieved. Histopathological examination confirmed a WHO grade I schwannoma. Postoperative recovery was uneventful, with improvement in neuropsychological and left-sided olfactory function. There was no residual lesion on follow-up MRI. DISCUSSION AND CONCLUSIONS: OGS should be included in the differential diagnosis of anterior skull base tumors with cystic or sinonasal extension. In selected cases, a combined cranio-endoscopic approach allows safe and radical resection while minimizing morbidity. Accurate histopathological evaluation remains essential for definitive diagnosis, as radiological features alone may be misleading. Olfactory function should be systematically measured since preservation and even improvement of olfactory function are possible. This supports a non-olfactory origin of the tumor, suggesting secondary compression rather than primary involvement of the olfactory system.