Clinical and Imaging Evaluation of COVID-19-Related Olfactory Dysfunction

Abstract

Background Olfactory dysfunction has been reported in 47.85% of COVID patients. It can be broadly categorized into conductive or sensorineural olfactory loss. Conductive loss occurs due to impaired nasal air flow, while sensorineural loss implies dysfunction of the olfactory epithelium or central olfactory pathways. Objectives The aim of this study was to analyze the clinical and imaging findings in patients with COVID-related olfactory dysfunction. Additionally, the study aimed to investigate the possible mechanisms of COVID-related olfactory dysfunction. Methods The study included 110 patients with post-COVID-19 olfactory dysfunction, and a control group of 50 COVID-negative subjects with normal olfactory function. Endoscopic nasal examination was performed for all participants with special focus on the olfactory cleft. Smell testing was performed for all participants by using a smell diskettes test. Olfactory pathway magnetic resonance imaging (MRI) was done to assess the condition of the olfactory cleft and the dimensions and volume of the olfactory bulb. Results Olfactory dysfunction was not associated with nasal symptoms in 51.8% of patients. MRI showed significantly increased olfactory bulb dimensions and volume competed to controls. Additionally, it revealed olfactory cleft edema in 57.3% of patients. On the other hand, radiological evidence of sinusitis was detected in only 15.5% of patients. Conclusion The average olfactory bulb volumes were significantly higher in the patients’ group compared to the control group, indicating significant edema and swelling in the olfactory bulb in patients with COVID-related olfactory dysfunction. Furthermore, in most patients, no sinonasal symptoms such as nasal congestion or rhinorrhea were reported, and similarly, no radiological evidence of sinusitis was detected. Consequently, the most probable mechanism of COVID-related olfactory dysfunction is sensorineural loss through virus spread and damage to the olfactory epithelium and pathways.

A Comprehensive Review of COVID-19-Related Olfactory Deficiency: Unraveling Associations with Neurocognitive Disorders and Magnetic Resonance Imaging Findings

“…Additionally, we have investigated cognitive and mood deficits associated with post-COVID OD and possible available treatments. The MRI studies for COVID-19-related OD employed various methodologies, assessing structural and functional aspects of the olfactory system through various parameters [2,4,[34][35][36][37][38][39][40][41][44][45][46]. Evaluation of OBV and the OS depth, common parameters in different studies, revealed a consistent reduction in OBV and OS depth in post-COVID-19 patients with OD, suggesting direct damage to olfactory neural pathways [2,35,[37][38][39][40]44,46].…”

“…In fact, they found significant decreases in the values of both OBV and OS depth. Instead, Abdou et al [41], in a study that compared 110 patients with post-COVID-19 OD and a control group of 50 normal subjects, showed significantly increased OB dimensions (length × width × height) and volume compared with controls. They hypothesize that the mechanism underlying COVID-related OD is sensorineural loss through virus spread and damage to the OE and pathways.…”

Neuropsychiatric consequences of COVID-19 related olfactory dysfunction: could non-olfactory cortical-bound inputs from damaged olfactory bulb also contribute to cognitive impairment?

“…OB is transmitting ascending olfactory sensation as well as mechanoceptive signal of rhythmic nasal airflow and is receiving “top-down” information related to olfactory processing (from ctx, HPC, Amygdala) as well as oscillatory drive (e.g. theta, gamma from HPC); reports of its possible COVID-19 inflammatory damage are not fully consistent (Sherif et al, 2022 ; Abdou et al, 2023 ; Muccioli et al, 2023 ). Piriform cortex is the primary target of the olfactory tract where cortical processing of olfactory information involves RRO-driven local gamma oscillations (Gonzalez et al, 2023 ) and is transmitted to other cortical structures, oscillatory coupled at different frequencies [including RRO (Mofleh and Kocsis, 2021a )], for further processing in the context of different cognitive functions.…”

Assessment of chorda tympani function after endoscopic and microscopic middle ear surgery

“…Olfactory and taste dysfunction have been reported in up to 47% of COVID-19 patients [ 11 – 13 ]. Regarding the concern of COVID-19 affecting taste among the study population, this confounding factor was excluded.…”