OBJECTIVE: To investigate whether olfactory bulb (OB) morphology is associated with olfactory recovery following olfactory training (OT) in individuals with COVID-19-related smell loss.

STUDY DESIGN: Prospective observational study.

SETTING: University hospital and research center.

METHODS: Twenty women with COVID-19-associated olfactory dysfunction and 19 healthy controls underwent OT for 3 months. OB shape (oval vs non-oval) was classified using high-resolution magnetic resonance imaging (MRI), and bilateral OB volumes were manually segmented before and after OT. Olfactory performance was assessed with the Sniffin' Sticks test. Statistical analyses included independent t tests, multimodal analysis of covariance, correlation analyses, and generalized estimating equations.

RESULTS: At baseline, OB volume correlated significantly with olfactory performance. Changes in left OB volume were positively correlated with changes in odor threshold. Following OT, patients with non-oval OB shapes showed greater improvement in Threshold + Discrimination + Identification (TDI) scores and enlargement of left OB volume compared to those with oval-shaped OB. However, OB morphology did not significantly change over time in both patients and controls.

CONCLUSION: OB shape may provide a novel perspective for predicting prognosis after OT. Further studies with larger cohorts and extended training durations are warranted to validate these preliminary observations.