Olfactory Bulb MRI and Paranasal Sinus CT Findings in Persistent COVID-19 Anosmia

Abstract

Background and purpose There is limited literature consisting of case reports or series on olfactory bulb imaging in COVID-19 olfactory dysfunction. An imaging study with objective clinical correlation is needed in COVID-19 anosmia in order to better understand underlying pathogenesis. Material and methods We evaluated 23 patients with persistent COVID-19 olfactory dysfunction. Patients included in this study had a minimum 1-month duration between onset of olfactory dysfunction and evaluation. Olfactory functions were evaluated with Sniffin’ Sticks Test. Paranasal sinus CTs and MRI dedicated to olfactory nerves were acquired. On MRI, quantitative measurements of olfactory bulb volumes and olfactory sulcus depth and qualitative assessment of olfactory bulb morphology, signal intensity and olfactory nerve filia architecture were performed. Results All patients were anosmic at the time of imaging based on olfactory test results. On CT, Olfactory cleft opacification was seen in 73.9% of cases with a mid and posterior segment dominance. 43.5% of cases had below normal olfactory bulb volumes and 60.9% of cases had shallow olfactory sulci. 54.2% of cases had changes in normal inverted J shape of the bulb. 91.3% of cases had abnormality in olfactory bulb signal intensity in the forms of diffusely increased signal intensity, scattered hyperintense foci or microhemorrhages. Evident clumping of olfactory filia was seen in 34.8% of cases and thinning with scarcity of filia in 17.4%. Primary olfactory cortical signal abnormality was seen in 21.7% of cases. Conclusion Our findings indicate olfactory cleft and olfactory bulb abnormalities are seen in COVID-19 anosmia. There was a relatively high percentage of olfactory bulb degeneration. Further longitudinal imaging studies could shed light on the mechanism of olfactory neuronal pathway injury in COVID-19 anosmia.

The temporal course of COVID-19 anosmia and relation to other clinical symptoms

“…Available literature supports spontaneous improvement with a mean duration of 2-3 weeks [23,24]. However, cases with symptoms lasting more than 1 month, so called persistent anosmia, have also been reported [25][26][27]. Considering the fact that olfactory epithelium undergoes regeneration over 6-8 weeks, SARS-COV2 may result in anosmia longer than 2-3 weeks due to the epithelia damage caused [28].…”

A narrative review on characterization of acute respiratory distress syndrome in COVID-19-infected lungs using artificial intelligence

“…Future research should look for a way to quickly determine the COVID-19 severity using a global positioning system in target lung regions in 2-D and 3-D images, while considering comorbidity and time constraints [ 236 ] [ 237 ] [ 238 ]. This fundamental study can also be further developed in several other directions, covering the fields of neurology [ 239 ], cardiology, diabetology [ 240 ], and ophthalmology [ 241 ].…”

Neurological infections in 2020: COVID-19 takes centre stage

“…Subsequently, hypotheses emerged regarding the potential for viral neurotropism and a direct route of entry into the CNS from the olfactory bulbs. In an imaging study 6 of 23 patients with confirmed SARS-CoV-2 infection with clinical anosmia, SARS-CoV-2-related olfactory dysfunction was differentiated from other viral olfactory dysfunction in several crucial ways. Post-viral anosmia in the setting of upper respiratory tract infections is usually related to mucosal congestion and nasal obstruction, resulting in a conductive olfactory loss; however, few patients with SARS-CoV-2-related anosmia had sinonasal symptoms, suggesting that mucosal congestion is an unlikely aetiology for anosmia in these cases.…”

“…Post-viral anosmia in the setting of upper respiratory tract infections is usually related to mucosal congestion and nasal obstruction, resulting in a conductive olfactory loss; however, few patients with SARS-CoV-2-related anosmia had sinonasal symptoms, suggesting that mucosal congestion is an unlikely aetiology for anosmia in these cases. 6 Olfactory epithelium support-cells residing in the olfactory cleft express the angiotensin-converting enzyme 2 receptor, identified as the binding antigen for SARS-CoV-2. 6 Imaging of the olfactory cleft showed olfactory cleft opacification in 17 (74%) of cases.…”

“… 6 Olfactory epithelium support-cells residing in the olfactory cleft express the angiotensin-converting enzyme 2 receptor, identified as the binding antigen for SARS-CoV-2. 6 Imaging of the olfactory cleft showed olfactory cleft opacification in 17 (74%) of cases. 6 Moving proximally, olfactory nerve filia clumping, suggestive of inflammation, was observed in eight (35%) of patients, and olfactory bulb signal abnormalities, indicating degeneration or microhaemorrhage, were seen in 21 (91%) individuals.…”