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CC BY-NC-ND 4.0 · Indian J Radiol Imaging
DOI: 10.1055/s-0045-1811932
Original Article

Exploring Olfactory Bulb Volume and Its Shrinkage in Aging and Neurodegeneration: A Systematic Review and Meta-Analysis of Observational Studies

Authors

  • Adil Asghar

    1   Department of Anatomy, All India Institute of Medical Sciences, Patna, Bihar, India

  • Ravi Kant Narayan 

    2   Department of Anatomy, All India Institute of Medical Sciences, Bhubaneshwar, Odisha, India

  • Rajesh Kumar 

    1   Department of Anatomy, All India Institute of Medical Sciences, Patna, Bihar, India

  • Pradosh Kumar Sarangi 

    3   Department of Radiodiagnosis, All India Institute of Medical Sciences, Deoghar, Jharkhand, India

  • Apurba Patra 

    4   Department of Anatomy, All India Institute of Medical Sciences, Bathinda, Punjab, India

  • Ashutosh Kumar

    1   Department of Anatomy, All India Institute of Medical Sciences, Patna, Bihar, India

  • Md Zabihullah

    5   Department of Physiology, All India Institute of Medical Sciences, Patna, Bihar, India

Funding None.
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Abstract

Background

The olfactory bulb (OB) plays a crucial role in processing smells and has significant neuroplasticity throughout life. Age-related changes in OB volume (OBV) are associated with declining olfactory function, potentially impacting quality of life and serving as an early marker of neurodegenerative diseases. This study conducted a meta-analysis to assess OBV changes across diverse age groups in healthy individuals, explored its association with olfactory function, and further examined OB atrophy in Parkinson's disease (PD) and Alzheimer's disease (AD).

Materials and Methods

A systematic review and meta-analysis were conducted following PRISMA guidelines. Studies evaluating OBV through MRI in healthy individuals and patients with PD or AD were included. Data were extracted on age, sex, olfactory function, and OBV. Meta-regression was performed to assess the correlation between OBV and age, while subgroup analyses examined the effects of sex and laterality.

Results

Twenty-nine studies were analyzed, including 12 on healthy individuals, 7 on AD, and 11 on PD. The pooled mean OBV was 54.5 mm3 (95% CI, 42.03–66.98) for the right OB and 55.56 mm3 (95% CI, 42.96–68.15) for the left OB, with no significant sex or laterality differences. OBV showed a moderate negative correlation with age (r = −0.53 to −0.59, p < 0.05), suggesting progressive atrophy with aging. Olfactory function, assessed through the Threshold, Differentiation, and Identification (TDI) and the University of Pennsylvania Smell Identification Test (UPSIT) scores, was also moderately correlated with OBV (r = 0.48, p < 0.01). In neurodegenerative diseases, OBV reduction was greater, with shrinkage of 0.9 to 0.93 SD in PD and 1 to 1.05 SD in AD, primarily attributed to pathological degeneration.

Conclusion

Age-related OBV reduction is a normal physiological process with a moderate impact on olfactory function. While neurodegenerative diseases exacerbate OB atrophy, at least 40% of OB shrinkage observed in PD appears to be age-related. OBV could serve as a potential biomarker for aging and early neurodegeneration.

Keywords

olfactory bulb - olfactory dysfunction - aging - magnetic resonance imaging - neurodegenerative diseases - Parkinson's disease - Alzheimer's disease

Data Availability Statement

All available data have been included in the manuscript.


Ethical Approval

Not applicable.


Patients' Consent

Patient consent is not required.


Supplementary Material



Publikationsverlauf

Artikel online veröffentlicht:
16. September 2025

© 2025. Indian Radiological Association. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/)

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