Diffusion-weighted imaging measurements of central smell regions in COVID-19 patients: insular gyrus, corpus amygdala, and thalamus

OBJECTIVE: The aim of this study was to investigate central smell centers with cranial magnetic resonance imaging (MRI) diffusion-weighted imaging (DWI) in COVID-19. PATIENTS AND METHODS: This retrospective study evaluated cranial MRI images of 54 adults. The experimental group (Group 1), consisting of 27 patients with positive COVID-19 real-time polymerase chain reaction (RT-PCR) assays, was compared to the control group (Group 2), comprising 27  healthy controls without COVID-19. The apparent diffusion coefficient (ADC) values were measured in the corpus amygdala, thalamus, and insular gyrus in both groups. RESULTS: Thalamus ADC values of the COVID-19 group were significantly lower compared to the control group bilaterally. However, no differences were found in the insular gyrus and corpus amygdala ADC values between the two groups. Positive correlations were observed between the insular gyrus and corpus amygdala ADC values and the thalamus ADC values. Insular gyrus ADC values (right) were higher in females. Left insular gyrus and corpus amygdala ADC values were higher in COVID-19 patients with smell loss. Right insular gyrus and left corpus amygdala ADC values were lower in COVID-19 patients with lymphopenia. CONCLUSIONS: Diffusion restriction in olfactory areas can be considered an obvious indicator that the COVID-19 virus affects and damages the immune system at the neuronal level. Given the urgency and lethality of the current pandemic, acute onset odor loss should be considered a high suspicion-adhesive index for patients with SARS-CoV-2 infection. Therefore, the sense of smell should be considered and evaluated simultaneously with other neurological symptoms. DWI should be widely used as an early imaging method for central nervous system (CNS) infections, especially in relation to COVID-19