A Systematic Review of Imaging Studies in Olfactory Dysfunction Secondary to COVID-19

Rationale and Objectives: Hyposmia/anosmia is common among patients with coronavirus disease-2019 (COVID-19). Various imaging modalities have been used to assess olfactory dysfunction in COVID-19. In this systematic review, we sought to categorize and summarize the imaging data in COVID-19-induced anosmia. Material and Methods: Eligible articles were included after a comprehensive review using online databases including Google scholar, Scopus, PubMed, Web of science and Elsevier. Duplicate results, conference abstracts, reviews, and studies in languages other than English were excluded. Results: In total, 305 patients undergoing MRI/functional MRI (177), CT of paranasal sinuses (129), and PET/CT or PET/MRI scans (14) were included. Out of a total of 218 findings reported on MRI, 80 were reported on early (< 1 month) and 85 on late (>1 month) imaging in relation to the onset of anosmia. Overall, OB morphology and T2-weighted or FLAIR signal intensity were normal in 68/218 (31.2%), while partial or complete opacification of OC was observed in 60/218 (27.5%). T2 hyperintensity in OB was detected in 11/80 (13.75%) and 18/ 85 (21.17%) on early and late imaging, respectively. Moreover, OB atrophy was reported in 1/80 (1.25%) on early and in 9/85 (10.58%) on late imaging. Last, among a total of 129 CT scans included, paranasal sinuses were evalualted in 88 (68.21%), which were reported as normal in most cases (77/88, [87.5%]). Conclusion: In this systematic review, normal morphology and T2/FLAIR signal intensity in OB and OC obstruction were the most common findings in COVID-19-induced anosmia, while paranasal sinuses were normal in most cases. OC obstruction is the likely mechanism for olfactory dysfunction in COVID-19. Abnormalities in OB signal intensity and OB atrophy suggest that central mechanisms may also play a role in late stage in COVID-19-induced anosmia.

Automated summary

This systematic review of imaging data in COVID-19-induced anosmia found that normal morphology and T2/FLAIR signal intensity in olfactory bulb and obstruction of olfactory cleft were common, while paranasal sinuses were mostly normal. Olfactory cleft obstruction may be the mechanism for olfactory dysfunction in COVID-19, and abnormalities in olfactory bulb signal intensity and atrophy suggest central mechanisms may also play a role in late stage COVID-19-induced anosmia.