Normative Parameters of Olfactory Bulbs Based on Magnetic Resonance Imaging and Olfactory Function.

Background: Olfactory dysfunction is a frequently encountered sensory disorder that increases with aging, assessed magnetic resonance imaging (MRI); however, reference quantitative values for associated anatomical structures have rarely been suggested. The aim of this study was to assess the parameters of the olfactory bulbs (OBs) and olfactory sulcus (OS) in Korean adults according to age, along with their olfactory function.

Methods: We retrospectively evaluated 217 consecutive patients (104 men, 113 women; mean age, 52.4 ± 15.6 years) who underwent sellar MRI and olfactory function testing before transsphenoidal approach at a single tertiary center from March 2022 to December 2023. Based on the T2-weighted MRI, we evaluated the quantitative size parameters and morphological features of patients' OB and OS, along with their olfactory function test scores. We assessed the relationship between OB volume and age in pairwise correlations.

Results: The mean OB volume was 45.6 ± 15.3 mm³ in all patients. The patients' mean Korean version of the Sniffin' Sticks (KVSS) test II score was 26.8 ± 4.1. OB volume (P < 0.001), height (P < 0.001), and anteroposterior diameter (APD) (P < 0.001) differed significantly among the different age groups. Reduced OB volume was significantly associated with aging (r = -0.58, P < 0.001) and a decline in olfactory function scores (r = 0.34, P < 0.001).

Conclusion: Based on MRI, we proposed reference OB and OS values in adults of different age groups, highlighting the reduction in OB parameters, especially height and APD along with volume associated with aging and olfactory decline. These values can be useful for evaluating adult patients undergoing MRI for olfactory dysfunction.