18FDG PET/CT Scan Reveals Hypoactive Orbitofrontal Cortex in Anosmia of COVID-19

Abstract

During the current nascent pandemic, anosmia has been increasingly reported among patients with coronavirus disease-2019 (COVID-19) (1). While postviral olfactory loss secondary to nasal congestion or conductive pathway alteration is a known sequela of sinonasal viral infections (2), anosmia of COVID-19 is less commonly associated with rhinorrhea or nasal congestion (3). This may indicate sensory neural loss as the underlying cause of the olfactory dysfunction rather than the conductive mechanism in most cases of postviral olfactory loss. We have recently reported normal morphology of the olfactory bulb on magnetic resonance imaging in anosmia of COVID-19 (4). Whether there is decreased neural activity in olfactory pathways despite normal morphology is unknown. We sought to assess the neural metabolic activity in anosmia of COVID-19 by 18fluoro-2-deoxy-d-glucose (18FDG) positron emission tomographyÀcomputed tomography (PET-CT). We included a 27-year-old healthy, right-handed woman, diagnosed with COVID-19 by polymerase chain reaction assay. The patient had persistent isolated anosmia for 6 weeks. She had no history of alcohol intake or tobacco smoking and no background of psychiatric problems. The patient was asked to fast for 6 hours prior to imaging. We performed 18FDG-PET/CT in a neutral environment using 5 ml of aerosolized 0.9% NaCl delivered with O 2 at 3.5 ml/min via facial mask for 9 minutes. The patient was instructed to breath normally without sniffing. After 3 minutes, the patient received intravenous 18FDG (4.6 Megabecquerel/kg, Masih Daneshvari Hospital, Tehran), and the neutral olfactory condition continued for another 6 minutes. The patient laid down in a semi-darkened,

Prevalence of hyposmia and hypogeusia in 390 COVID-19 hospitalized patients and outpatients: a cross-sectional study

“…Therefore, there could be a direct contact and interaction with a possible cytopathic effect of SARS-CoV-2 on ACE2-expressing neurosensory receptor cells [28]. Given the prevalence of hyposmia in COVID-19 and the higher frequency in non-severe patients that appears in our study, damage to olfactory receptors in the epithelium of the nasal mucosa or in the olfactory bulbs seems more likely than central cortical involvement [25].…”

“…Four reports of the findings on nasal cavity and brain magnetic resonance imaging (MRI) in patients with COVID-19 and sudden olfactory loss found various results: no abnormality [21], bilateral obstructive inflammation of olfactory clefts without anomalies of the OB and tracts [22], bilateral transient OB edema [23], and transient cortical hyperintensity in the right gyrus rectus and in the OB [24]. Furthermore, a report of a decreased metabolic activity in the orbitofrontal cortex on a 18− FDG PET/CT scan of a patient with COVID-19-related anosmia suggested that there could be an impaired neural activity in olfactory pathways despite normal morphology [25].…”

Coronavirus Disease 2019 (COVID-19) in Molecular Imaging: A Systematic Review of Incidental Detection of SARS-CoV-2 Pneumonia on PET Studies

“…In this era, a unique advantage of whole-body PET/CT over competing for imaging modalities is the potential for detection of additional incidental metabolically active lesions throughout the rest of the body in a single acquisition. Karimi et al 18 (no. 34) have reported reduced activity in the orbitofrontal cortex in COVID-19-associated anosmia, which might indicate an impaired neural function as the underlying pathology of anosmia, due to SARS-CoV-2 neurotropism.…”

“…Moreover, we reported one patient in our center ( Fig. 2 ) and a series of PET/CT images from three included studies 16 , 17 , 18 via formal permissions obtained from their publishers. ( Fig 3 - 5 )

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“…The uptake of temporal lobes was symmetric and normal (arrows, D). Images obtained from Karimi-Galougahi et al, 18 Academic Radiology , July 2020, Vol. 27(7):1042-1043, and permission to use granted by Elsevier and Copyright Clearance Center …”