Olfactory function after nasoseptal flap reconstruction in skull base surgery: a systematic review and meta-analysis.

BACKGROUND: Endoscopic skull base surgery is widely used for various skull base pathologies. The nasoseptal flap (NSF) is considered the gold-standard reconstructive technique to reduce postoperative cerebrospinal fluid (CSF) leaks. However, its impact on olfactory function remains unclear. OBJECTIVE: To systematically compare olfactory outcomes between NSF and no-NSF reconstruction following skull base surgery. METHODS: PubMed, Embase, and Cochrane databases were searched for randomized controlled trials and observational studies comparing olfactory function in patients undergoing skull base surgery with NSF versus no-NSF reconstruction. Outcomes included: (1) number of patients with any degree of postoperative decline in olfaction at ≥ 6 months, (2) mean olfactory scores at 3 months, and (3) mean olfactory scores at ≥ 6 months. Heterogeneity was assessed using I² statistics. RESULTS: Seven studies (n = 1,289) were included; 392 patients (30.4%) underwent NSF reconstruction. NSF was associated with a greater number of patients who experienced postoperative olfactory decline compared to no-NSF (RR 1.77; 95% CI 1.20-2.62; p = 0.004). At 3 months, NSF patients had worse olfactory scores (SMD - 0.32; 95% CI - 0.60 to - 0.05; p = 0.02). However, no significant difference in olfactory scores was observed at ≥ 6 months (SMD - 0.43; 95% CI - 1.63 to 0.77; p = 0.33). CONCLUSION: NSF reconstruction is associated with worse short-term olfactory test scores and a higher proportion of patients with olfactory decline at ≥ 6 months. However, the severity of dysfunction at longer-term follow-up is comparable between groups, suggesting delayed but eventual olfactory recovery.