Hippocampal Volume Shown on MRI Correlates with Olfactory Performance in Patients with Cognitive Impairment

by Linda Kossoff •

What neurodegenerative changes can be observed with magnetic resonance imaging (MRI) in patients with olfactory impairment and mild cognitive impairment (MCI) or dementia?

BOTTOM LINE

Hippocampal volume appears to correlate with olfactory performance in individuals with cognitive impairment, and olfactory functional MRI (fMRI) may improve early detection of Alzheimer’s disease (AD).

BACKGROUND: The association between olfactory and cognitive impairment is well established. Neurogenerative changes detected on structural MRI or changes to the olfactory network or activation volume seen on fMRI may help explain the underlying mechanism behind this association. With other screening tools, MRI may improve prediction of future cognitive decline.

STUDY DESIGN: Systematic review.

SETTING: Department of Otolaryngology–Head and Neck Surgery, Johns Hopkins School of Medicine, Baltimore, Md.

SYNOPSIS: Researchers conducted a literature search for studies with MRI and olfactory testing among participants diagnosed with MCI or dementia. They identified 24 studies that met their criteria, including four case series, 16 cross-sectional reviews, and four prospective cohorts. Combined population size totaled 3,150. Of the studies, 18 included participants with MCI and 16 with AD dementia. Nineteen studies included cognitively normal controls. Seventeen studies reported hippocampal volume findings, with the majority noting a relationship between atrophy and olfactory performance. Five studies reported olfactory fMRI findings, highlighting the utility of olfactory fMRI to identify individuals in the early stages of cognitive decline. Hippocampal volume atrophy was the most reported neurodegenerative find that correlated with olfactory testing scores among cross-sectional studies, but prospective studies showed mixed evidence regarding hippocampal volume as a predictor of cognitive decline. Authors concluded that the correlation between olfactory impairment and neurodegenerative markers on MRI supports odor identification tests as a cost-effective screening tool for progression to dementia and suggests a potential near-term use of MRI for treatment trials in high-risk patients.

CITATION: Yi JS, Hura N, Roxbury CR, et al. Magnetic resonance imaging findings among individuals with olfactory and cognitive impairment. Laryngoscope. 2022;132:177-187.