Olfactory Nerve Schwannoma: a case series with a systematic review of the literature focusing risk factors, etiology, clinical presentation, and management

Objective: Olfactory Nerve Schwannomas (ONS) affect cranial nerve I (CN I), responsible for the sense of smell. This systematic review aims to comprehensively examine the risk factors, etiology, clinical presentation, and management of ONS by analyzing 44 case reports/series published from 1978 to 2022. Methods: Our systematic review utilized a comprehensive search strategy across various scientific databases, including PubMed, Scopus, and Web of Science in March 2023. The inclusion and exclusion criteria included minimum information on demographics (i.e., age), clinical presentation, syndrome, area involved, and extent of resection. The selected articles were case reports, so there is no question about bias. Articles were meticulously reviewed for the above information and underwent both qualitative and quantitative analysis. Results: A total of 44 case reports/series, consisting of 45 patients, were included in this study (mean: 38.45). The anterior cranial fossa was the most frequently involved area (48 %). The most common surgical procedure was bifrontal craniotomy (n=16), followed by left frontal craniotomy (n=7). Approximately 95.5 % of patients underwent Gross Total Resection (GTR), while 4.5 % had Subtotal Resection (STR). Radiotherapy was applied to two patients. Olfactory function varied, with 35.5 % preserving it and 28.88 % experiencing damage or loss. Positive outcomes were observed in approximately 66.6 % of cases, with complications reported in 15 % of instances, including cerebrospinal fluid (CSF) rhinorrhea and diplopia. Conclusions: Long-term follow-up and regular screening of patients are imperative. Further research is essential to elucidate the precise pathogenesis and to develop improved treatment modalities for ONS. This review provides a comprehensive overview of the current state of knowledge regarding ONS; however, as the disease is very rare, only case reports are available as a primary study, making it difficult to reach a strong conclusion.