Comprehensive MRI analysis of olfactory bulb morphology and olfactory sulcus depth in chronic rhinosinusitis, migraine, and post-COVID patients

OBJECTIVE: This study aimed to provide a comprehensive MRI-based assessment of olfactory bulb (OB) morphology and olfactory sulcus (OS) depth in patients with chronic rhinosinusitis (CRS), post-COVID, and migraine, representing distinct etiologies of olfactory dysfunction. METHODS: High-resolution T2-weighted MRI scans were analyzed in 88 participants (20 post-COVID, 30 migraine, 18 CRS; mean age = 41.32 ± 13.91). OB volume, height, width, and anterior-posterior diameter (APD), as well as OS depth, were measured bilaterally. OB shape was classified as oval, flat, or irregular. Group differences were assessed using ANOVA, and correlations with olfactory performance (Sniffin' Sticks threshold, discrimination, identification, and TDI scores) were examined. RESULTS: OB volume, height, and width were generally larger in controls than in patient groups, with no significant differences between patient groups. Olfactory performance was preserved in migraine but reduced in post-COVID and CRS. Positive correlations between OB volume/width and olfactory function were observed in controls, migraine, and CRS, whereas post-COVID patients showed a negative association with OB width. Shape analysis revealed reduced symmetry and more atypical forms, particularly in CRS. CONCLUSIONS: OB atrophy was present across patient groups, but its relationship with olfactory function differed by condition. While OB volume remains a sensitive marker, additional measures such as width, shape, and OS depth provide complementary insights. Structural alterations may reflect underlying olfactory system impairment rather than direct functional loss. Increased asymmetry, especially left-sided atypical forms in CRS, suggests potential lateralized vulnerability. Overall, a multidimensional structural assessment enhances understanding of olfactory dysfunction.