Magnetic resonance imaging findings in COVID-19-related anosmia.

BACKGROUND: The coronavirus disease 2019 (COVID-19) mostly manifests with fever, shortness of breath, and cough, has also been found to cause some neurological symptoms, such as anosmia and ageusia. The aim of the study was to present the magnetic resonance imaging (MRI) findings of patients with anosmia-hyposmia symptoms and to discuss potential mechanisms in light of these findings. METHODS: Of the 2412 patients diagnosed with COVID-19-related pneumonia (RT-PCR at least once + clinically confirmed) between March and December 2020, 15 patients underwent olfactory MRI to investigate the cause of ongoing anosmia/ hyposmia symptoms were included in the study. RESULTS: Eleven (73.3%) patients were female and four (26.7%) were male. A total of eight patients (53.3%) showed thickening in the olfactory cleft region, where the olfactory epithelium is located. In nine patients (60%), enhancement was observed in the olfactory cleft region. Diffusion-weighted imaging showed restricted diffusion in three patients (20%) (corpus callosum splenium in one patient, thalamus mediodorsal nucleus in one patient, and mesencephalon in one patient). DISCUSSION: This study revealed that there is a relationship between anosmia and MRI findings. Larger studies can enlighten the pathophysiological mechanism and shed light on both diagnosis and new treatments.

Transient modifications of the olfactory bulb on MR follow-up of COVID-19 patients with related olfactory dysfunction.

BACKGROUND: Olfactory dysfunction (OD) has been reported with a high prevalence on mild to moderate COVID-19 patients. Previous reports suggest that volume and signal intensity of olfactory bulbs (OB) have been reported as abnormal on acute phase of COVID-19 anosmia, but a prospective MRI and clinical follow-up study of COVID-19 patients presenting with OD was missing, aiming at understanding the modification of OB during patients'follow-up. METHODS: A prospective multicenter study was conducted including 11 COVID-19 patients with OD. Patients underwent MRI and psychophysical olfactory assessments at baseline and 6-month post-COVID-19. T2 FLAIR-Signal intensity ratio (SIR) was measured between the average signal of the OB and the average signal of white matter. OB volumes and obstruction of olfactory clefts (OC) were evaluated at both evaluation times. RESULTS: The psychophysical evaluations demonstrated a 6-month recovery in 10/11 patients (90.9%). The mean values of OB-SIR significantly decreased from baseline (1.66±0.24) to 6-month follow-up (1.35±0.27), reporting a mean variation of -17.82±15.20 % (p<0.001). The mean values of OB volumes significantly decreased from baseline (49.22±10.46 mm3) to 6-month follow-up (43.70±9.88 mm3), (p=0.006). CONCLUSION: Patients with demonstrated anosmia reported abnormalities in OB imaging that may be objectively evaluated with the measurement of SIR and OB volumes. SIR and OB volumes significantly normalized when patient recovered smell. This supports the underlying mechanism of a transient inflammation of the OB as a cause of Olfactory Dysfunction in COVID-19 patients.

Olfactory loss and brain connectivity after COVID-19.

To address the impact of COVID-19 olfactory loss on the brain, we analyzed the neural connectivity of the central olfactory system in recently SARS-CoV-2 infected subjects with persisting olfactory impairment (hyposmia). Twenty-seven previously SARS-CoV-2 infected subjects (10 males, mean age ± SD 40.0 ± 7.6 years) with clinically confirmed COVID-19 related hyposmia, and eighteen healthy, never SARS-CoV-2 infected, normosmic subjects (6 males, mean age ± SD 36.0 ± 7.1 years), were recruited in a 3 Tesla MRI study including high angular resolution diffusion and resting-state functional MRI acquisitions. Specialized metrics of structural and functional connectivity were derived from a standard parcellation of olfactory brain areas and a previously validated graph-theoretic model of the human olfactory functional network. These metrics were compared between groups and correlated to a clinical index of olfactory impairment. On the scanning day, all subjects were virus-free and cognitively unimpaired. Compared to control, both structural and functional connectivity metrics were found significantly increased in previously SARS-CoV-2 infected subjects. Greater residual olfactory impairment was associated with more segregated processing within regions more functionally connected to the anterior piriform cortex. An increased neural connectivity within the olfactory cortex was associated with a recent SARS-CoV-2 infection when the olfactory loss was a residual COVID-19 symptom. The functional connectivity of the anterior piriform cortex, the largest cortical recipient of afferent fibers from the olfactory bulb, accounted for the inter-individual variability in the sensory impairment. Albeit preliminary, these findings could feature a characteristic brain connectivity response in the presence of COVID-19 related residual hyposmia.

18F-FDG brain PET hypometabolism in post-SARS-CoV-2 infection: substrate for persistent/delayed disorders?

PURPOSE: Several brain complications of SARS-CoV-2 infection have been reported. It has been moreover speculated that this neurotropism could potentially cause a delayed outbreak of neuropsychiatric and neurodegenerative diseases of neuroinflammatory origin. A propagation mechanism has been proposed across the cribriform plate of the ethmoid bone, from the nose to the olfactory epithelium, and possibly afterward to other limbic structures, and deeper parts of the brain including the brainstem. METHODS: Review of clinical examination, and whole-brain voxel-based analysis of 18F-FDG PET metabolism in comparison with healthy subjects (p voxel < 0.001, p-cluster < 0.05, uncorrected), of two patients with confirmed diagnosis of SARS-CoV-2 explored at the post-viral stage of the disease. RESULTS: Hypometabolism of the olfactory/rectus gyrus was found on the two patients, especially one with 4-week prolonged anosmia. Additional hypometabolisms were found within amygdala, hippocampus, parahippocampus, cingulate cortex, pre-/post-central gyrus, thalamus/hypothalamus, cerebellum, pons, and medulla in the other patient who complained of delayed onset of a painful syndrome. CONCLUSION: These preliminary findings reinforce the hypotheses of SARS-CoV-2 neurotropism through the olfactory bulb and the possible extension of this impairment to other brain structures. 18F-FDG PET hypometabolism could constitute a cerebral quantitative biomarker of this involvement. Post-viral cohort studies are required to specify the exact relationship between such hypometabolisms and the possible persistent disorders, especially involving cognitive or emotion disturbances, residual respiratory symptoms, or painful complaints.

Olfactory bulb magnetic resonance imaging in SARS-CoV-2-induced anosmia in pediatric cases.

In this paper, we report three cases of pediatric patients with COVID-19 infection who presented with different symptoms and also anosmia and/or ageusia. The common feature of these 3 patients is that the smell and / or taste disorder developed without nasal symptoms such as nasal congestion, nasal obstruction or rhinorrhea. Although 40% of anosmies contains viral etiologies, COVID- 19 differs from other viral anosmies by the lack of nasal congestion and runny nose. Coronaviruses could invade the brain via the cribriform plate close to the olfactory bulb and the olfactory epithelium. We may expect some structural changes in the olfactory bulb so we evaluated our patient with cranial imaging.

Olfactory Cleft Measurements and COVID-19-Related Anosmia.

OBJECTIVE: This study aimed to investigate the differences in olfactory cleft (OC) morphology in coronavirus disease 2019 (COVID-19) anosmia compared to control subjects and postviral anosmia related to infection other than severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). STUDY DESIGN: Prospective. SETTING: This study comprises 91 cases, including 24 cases with anosmia due to SARS-CoV-2, 38 patients with olfactory dysfunction (OD) due to viral infection other than SARS-CoV-2, and a control group of 29 normosmic cases. METHODS: All cases had paranasal sinus computed tomography (CT), and cases with OD had magnetic resonance imaging (MRI) dedicated to the olfactory nerve. The OC width and volumes were measured on CT, and T2-weighted signal intensity (SI), olfactory bulb volumes, and olfactory sulcus depths were assessed on MRI. RESULTS: This study showed 3 major findings: the right and left OC widths were significantly wider in anosmic patients due to SARS-CoV-2 (group 1) or OD due to non-SARS-CoV-2 viral infection (group 2) when compared to healthy controls. OC volumes were significantly higher in group 1 or 2 than in healthy controls, and T2 SI of OC area was higher in groups 1 and 2 than in healthy controls. There was no significant difference in olfactory bulb volumes and olfactory sulcus depths on MRI among groups 1 and 2. CONCLUSION: In this study, patients with COVID-19 anosmia had higher OC widths and volumes compared to control subjects. In addition, there was higher T2 SI of the olfactory bulb in COVID-19 anosmia compared to control subjects, suggesting underlying inflammatory changes. There was a significant negative correlation between these morphological findings and threshold discrimination identification scores. LEVEL OF EVIDENCE: Level 4.

Clinical and Radiological Evaluations of COVID-19 Patients With Anosmia: Preliminary Report.

OBJECTIVES/HYPOTHESIS: To investigate clinical and radiological features of olfactory clefts of patients with mild coronavirus disease 2019 (COVID-19). STUDY DESIGN: Prospective non controlled study. METHODS: Sixteen COVID-19 patients were recruited. The epidemiological and clinical data were extracted. Nasal complaints were assessed through the 22-item Sino-Nasal Outcome Test. Patients underwent psychophysical olfactory testing, olfactory cleft examination, and computed tomography (CT) scans. RESULTS: Sixteen anosmic patients were included. The mean Sniffin' Sticks score was 4.6 ± 1.7. The majority of patients had no endoscopical abnormality, with a mean olfactory cleft endoscopy score of 0.6 ± 0.9. The olfactory clefts were opacified in three patients on the CT scan. The mean radiological olfactory cleft score was 0.7 ± 0.8. There were no significant correlations between clinical, radiological, and psychophysical olfactory testing. CONCLUSIONS: The olfactory cleft of anosmic COVID-19 patients is free regarding endoscopic examination and imaging. The anosmia etiology is not related to edema of the olfactory cleft. LEVEL OF EVIDENCE: 4 Laryngoscope, 130:2526-2531, 2020.

Anosmia and olfactory tract neuropathy in a case of COVID-19.

Coronavirus Disease-19 (COVID-19) has been in a global pandemic currently and relating symptoms were reported variously around the world. We reported a previously healthy man of COVID-19 presenting with anosmia as the obvious symptom with relevant radiological findings on brain magnetic resonance imaging.