The correlation between olfactory bulb volume and T&T odor threshold: a systematic review and meta-analysis.

This meta-analysis aims to quantitatively assess the correlation between olfactory bulb (OB) volume measured by magnetic resonance imaging (MRI) and the T＆T olfactometer identification threshold, with subgroup analyses conducted in patients with neurodegenerative disorders and healthy individuals. We searched PubMed, Web of Science, Embase, Cochrane Library, China Biology Medicine Disc (CBM), China National Knowledge Infrastructure (CNKI), Wanfang, and VIP databases for relevant studies. The procedure was under the guidance of the Preferred Systematic Reviews and Meta-Analyses Reporting Items (PRISMA) checklist. English or Chinese cross-sectional studies concerned with OB volume and olfactory function published before January 31, 2025, were searched in the data sources mentioned above. After study selection, data extraction, and the assessment of study quality, this meta-analysis was performed independently performed by two reviewers. Correlation coefficients were pooled using Fisher’s z transformation. Random- or fixed-effects models were applied according to heterogeneity. Subgroup analyses were conducted for neurodegenerative disorder patients and healthy controls. Fifteen studies concerning 1289 subjects were qualified for the study, including 824 patients who suffered from olfactory deficiency and 465 healthy individuals. Fourteen studies were of high quality, and one study was of medium quality. An overall correlation between OB volume and T＆T olfactory test score (r=-0.64, P= 0.01) was detected. Further subgroup analysis showed significant correlations among cognitive syndrome patients (mild cognitive impairment (MCI) and Alzheimer’s disease (AD)) (r=-0.84,P=0.82), Parkinson’s disease patients (PD) (r=-0.70,P=0.01), healthy subjects (r=-0.61,P=0.97). According to meta-regression analysis, age was not a source of heterogeneity. The result supported a significant correlation between OB volume and T＆T odor identification threshold. OB volume measurement may be a potential alternative for the T＆T odor identification test, especially in neurodegenerative individuals.