A Comparative Olfactory MRI, DTI and fMRI Study of COVID-19 Related Anosmia and Post Viral Olfactory Dysfunction

Abstract

Rationale and Objective: To evaluate how COVID-19 anosmia imaging findings resembled and differed from postinfectious olfactory Material and Methods: A total of 31 patients presenting with persistent COVID-19 related OD and 97 patients with post-infectious OD were included. Olfactory bulb MRI, DTI and olfactory fMRI findings in both groups were retrospectively assessed. Results: All COVID-19 related OD cases were anosmic, 18.6\% of post-infectious OD patients were hyposmic and remaining 81.4\% were anosmic. Mean interval between onset of OD and imaging was 1.5 months for COVID-19 related OD and 6 months for post-infectious OD. Olfactory bulb volumes were significantly higher in COVID-19 related OD than post-infectious OD. Deformed bulb morphology and increased olfactory bulb signal intensity was seen in 58.1\% and 51.6\% with COVID-19 related OD

and 63.9\% - 46.4\% with post-infectious OD

without significant difference. Significantly higher rate of olfactory nerve clumping and higher QA values at orbitofrontal and entorhinal regions were observed in COVID-19 related OD than post-infectious OD. Absence of orbitofrontal and entorhinal activity showed no statistically significant difference between COVID-19 related OD and postinfectious OD, however trigeminosensory activity was more robust in COVID-19 related OD cases. Conclusion: Olfactory bulb damage may play a central role in persistent COVID-19 related anosmia. Though there is decreased olfactory bulb volume and decreased white matter tract integrity of olfactory regions in COVID-19 related anosmia, this is not as pronounced as in other post-infectious OD. Trigeminosensory activity was more robust in COVID-19 related OD. These findings may reflect better preserved central olfactory system in COVID-19 related OD compared to COVID-19 related OD. (c) 2021 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.