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. Of all, 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.

Keywords: Anosmia; COVID-19; MRI; Olfactory bulb; Olfactory cleft; Olfactory nerve; Paranasal sinus CT.

Figure 1

(a) Normal J-shaped configuration of the olfactory bulb can be seen on the left side (delineated with dashed arrows) in a normal 20-year-old-female patient with no olfactory dysfunction. (b) An 18-year-old female patient with COVID-19 anosmia rectangular deformation of the olfactory morphology (delineated with dashed arrows).

Figure 2

A 52-year-old male patient with COVID-19 anosmia. Foci of hyperintensity is noted in the lateral part of right olfactory bulb (long arrow) and dorsolateral part of left olfactory bulb (short arrow) are noted.

Figure 3

A 22-year-old male patient with COVID-19 anosmia. Coronal T2-WI shows increased signal intensity in bilateral olfactory bulbs (arrow depicting the left sided signal abnormality). There is also surrounding incomplete hypointense halo surrounding the left sided signal abnormality (delineated on b).

Figure 4

A 30-year-old female patient with COVID-19 anosmia. Coronal T2-WI (a) show scattered foci of hypointensities. Sagittal image (b) better demonstrates the extent of the hypointense focus, consistent with microhemorrhages.

Figure 5

Representative image of a normal olfactory bulb on a sagittal T2 space image. Note the biconvex contours and regular signal intensity. The olfactory nerve filia are barely discernible with no clumping or replacement along the inferior margin by CSF signal intensity regions.

Figure 6

A 30-year-old male patient with COVID-19 anosmia. Sagittal T2-WI shows thickening and clumped appearance of the olfactory nerve filia (arrow).

Figure 7

A 37-year-old female patient with COVID-19 anosmia. Coronal 3D FLAIR image (a) shows diffuse increased in bilateral olfactory bulbs (more prominent on the right side, marked with arrow). More posterior coronal FLAIR image (b) at the level of olfactory stria shows subtle increased cortical signal intensity at primary olfactory cortex (arrow).