Functional and structural olfactory changes in post-COVID-19 patients detected by 7 Tesla MRI

Persistent olfactory dysfunction after SARS-CoV-2 infection is common, yet its central neural profile remains poorly defined. We combined ultra-high-field 7 Tesla resting-state functional MRI with surface-based cortical morphometry to characterise olfactory-network organisation and cortical structure in long-term post-COVID dysosmia. Thirty adults (14 with persistent dysosmia; 16 normosmic controls) completed psychophysical olfactory testing and 7 Tesla imaging. Connectivity analyses across 56 olfaction-related regions revealed a coherent pattern centred on insular, orbitofrontal and thalamic nodes: connectivity was reduced between the insula and the orbitofrontal and entorhinal cortices, and between the ventral posterior thalamus and the ventral insula, and increased between interhemispheric orbitofrontal regions and among anterior thalamic nuclei. Significant connections were predominantly right-lateralised or interhemispheric. Morphometry showed no volumetric differences but selective left orbitofrontal thinning. Across the whole sample, greater orbitofrontal and insular thickness was associated with better olfactory performance; however, this reflected the difference between patients and controls rather than a graded relationship within the patient group, and did not persist after accounting for group and age. Together, these findings provide a preliminary, proof-of-concept characterisation of an orbitofronto-insular signature of long-term post-COVID dysosmia and nominate candidate imaging markers for testing in larger, multi-centre cohorts.