The Associations Between Olfactory Bulb Morphology, Volume Change, and Olfactory Recovery

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

Prospective observational study.

University hospital and research center.

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.

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.

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.