The COVID-19 pandemic has affected millions worldwide, causing mortality and multi-organ morbidity. Neurological complications have been recognized. This study aimed to assess brain structural, microstructural, and connectivity alterations in patients with COVID-19-related olfactory or cognitive impairment using post-acute (time from onset: 264[208-313] days) multi-directional diffusion-weighted MRI (DW-MRI). The study included 16 COVID-19 patients with cognitive impairment (COVID-CM), 35 COVID-19 patients with olfactory disorder (COVID-OD), and 14 controls. A state-of-the-art processing pipeline was developed for DW-MRI pre-processing, mean diffusivity and fractional anisotropy computation, fiber density and cross-section analysis, and tractography of white-matter bundles. Brain parcellation required for probing network connectivity, region-specific microstructure and volume, and cortical thickness was based on T1-weighted scans and anatomical atlases. Compared to controls, COVID-CM patients showed overall gray matter atrophy (age and sex corrected p = 0.004), and both COVID-19 patient groups showed regional atrophy and cortical thinning. Both groups presented an increase in gray matter mean diffusivity (corrected p = 0.001), decrease in white matter fiber density and cross-section (corrected p < 0.05), , and COVID-CM patients also displayed an overall increased diffusivity (p = 0.022) and decreased anisotropy (corrected p = 0.038) in white matter. Graph-based analysis revealed reduced network modularity, with an extensive pattern of connectivity increase, in conjunction with a localized reduction in a few connections, mainly located in the left hemisphere. The left cingulate, anterior cingulate, and insula were primarily involved. Expanding upon previous findings, this study further investigated significant alterations in brain morphology, microstructure, and connectivity in COVID-19 patients with olfactory or cognitive disfunction. These findings suggest underlying neurodegeneration, neuroinflammation, and concomitant compensatory mechanisms. Future longitudinal studies are required to monitor the alterations over time and assess their transient or permanent nature.

COVID-19 neurological manifestations have been progressively recognized. Among available MRI techniques, diffusion weighted imaging (DWI) shows promise to study microstructure, inflammation, and edema. Previous DWI studies reported alterations in brain diffusivity in COVID-19 patients, as assessed by morphologic evaluation of brain DWI scans only. The aim of this study was to assess and quantify brain diffusion alterations in COVID-19 patients with neurological manifestations. 215 COVID-19 patients with neurological manifestations (olfactory and/or other neurological disorders) and 36 normal controls were compared and studied with DWI and T1-weighted MRI scans. MRI scans were processed by a semi-automatic processing procedure specifically developed for the purpose of this study, and the Apparent Diffusion Coefficient (ADC) was quantified in different brain tissues and individual white matter (WM) and gray matter (GM) regions. Differences in ADC values were assessed between COVID-19 patients and normal controls, as well as in the COVID-19 patient population grouped by hospitalization and neurological symptoms. Among COVID-19 patients (median [IQR] = 52 [42 - 60] years of age, 58 % females), 91 were hospitalized and 26 needed intensive care. 84 patients had hyposmia/ageusia only, while 131 ones showed other neurological disorders. COVID-19 patients showed significantly increased ADC values in the WM and in several GM regions (p < 0.001). ADC values were significantly correlated with MRI time from disease onset (p < 0.05). Hospitalized patients showed significantly higher ADC alteration than non-hospitalized patients in all brain tissues; similarly, COVID-19 patients with neurological disorders showed significantly higher ADC values than those with olfactory loss only. ADC alteration was highest in patients with cognitive or memory disorder and in those with encephalitis or meningitis. ADC values were neither associated with the duration of hospitalization nor with the need for intensive care. Current findings suggest DWI potential as a non-invasive marker of neuroinflammation in COVID-19, and the transient nature of the same. Future longitudinal studies are needed to confirm our findings.

Objective: The aim of this study was to assess COVID‐19‐related gray matter (GM) structural alterations in two distinct groups of patients presenting with the prevailing and distinctive COVID‐19‐related neurological symptoms – isolated olfactory disorders as sole neurological manifestation (COVID‐OD) and cognitive disorders (COVID‐CD) – as compared to a control group of unaffected individuals.Methods: The study included 61 COVID‐CD patients (57 [60–63] years, 62% females), 84 COVID‐OD patients (49 [35–57] years, 60% females), and 17 controls (51 [41–52] years, 41% females). Region‐based morphometry (RBM) and voxel‐based morphometry (VBM) were performed on T1‐weighted MRI scans to assess GM regional volume and voxel‐wise density differences between COVID‐19 patients and controls. Surface‐based morphometry (SBM) was applied to investigate cortical thickness alterations. The statistical models built to assess GM structural differences among groups included total intracranial volume and age as nuisance variables.Results: The multi‐morphometric analysis revealed statistically significant (p < 0.05 corrected for multiple comparisons) reduction in GM regional volumes, in voxel‐wise GM density and in cortical thickness in both COVID‐CD and COVID‐OD patient groups as compared to controls. Across all three analyses, COVID‐CD patients showed more distributed and severe GM loss than COVID‐OD patients. The most prominently affected GM regions in the COVID‐CD group included the hippocampus, putamen, cingulate gyrus, precuneus, precentral and postcentral gyri, amygdala, lingual gyrus, and caudate nucleus.Interpretation: Our MRI findings show that COVID‐19‐related olfactory and cognitive disorders both induce GM atrophy, although at different degrees of severity, likely indicative of neurodegeneration and neuroinflammation.

Background and objective Despite olfactory disorders being among the most common neurological complications of coronavirus disease 2019 (COVID-19), their pathogenesis has not been fully elucidated yet. Brain MR imaging is a consolidated method for evaluating olfactory system’s morphological modification, but a few quantitative studies have been published so far. The aim of the study was to provide MRI evidence of olfactory system alterations in patients with COVID-19 and neurological symptoms, including olfactory dysfunction. Methods 196 COVID-19 patients (median age: 53 years, 56% females) and 39 controls (median age 55 years, 49% females) were included in this cross-sectional observational study; 78 of the patients reported olfactory loss as the only neurological symptom. MRI processing was performed by ad-hoc semi-automatic processing procedures. Olfactory bulb (OB) volume was measured on T2-weighted MRI based on manual tracing and normalized to the brain volume. Olfactory tract (OT) median signal intensity was quantified on fluid attenuated inversion recovery (FLAIR) sequences, after preliminary intensity normalization. Results COVID-19 patients showed significantly lower left, right and total OB volumes than controls (p < 0.05). Age-related OB atrophy was found in the control but not in the patient population. No significant difference was found between patients with olfactory disorders and other neurological symptoms. Several outliers with abnormally high OT FLAIR signal intensity were found in the patient group. Conclusions Brain MRI findings demonstrated OB damage in COVID-19 patients with neurological complications. Future longitudinal studies are needed to clarify the transient or permanent nature of OB atrophy in COVID-19 pathology. Graphical abstract

Background: Concern may exist that pulmonary lesions associated with cystic airspaces are at risk of increased biopsy complications or lower biopsy accuracy given challenges in targeting tissue abutting or intermingled with the cystic airspaces. Objective: To evaluate the safety and diagnostic performance of CT-guided core-needle biopsy (CNB) of pulmonary lesions with cystic airspaces. Methods: This retrospective study included 90 patients (median age, 69.5 years; 28 female, 62 male) who underwent CT-guided CNB of pulmonary lesions associated with cystic airspaces (based on review of procedural images) from February 2010 to December 2022 and a matched control group (2:1 ratio) of 180 patients (median age, 68.0 years; 56 female, 124 male) who underwent CNB of noncystic noncavitary lesions during the same period. The groups were compared in terms of complications, nondiagnostic biopsies (i.e., nonspecific benignities, atypical cells, or insufficient specimens), and CNB diagnostic performance for detecting malignancy using as reference the final diagnosis from a joint review of all available records. For lesions associated with cystic airspaces that underwent surgical resection after CNB, histologic slides were re-reviewed to assess cystic airspace etiology. Results: The final diagnosis was malignant in 90% (81/90) of lesions associated with cystic airspaces and 92% (165/180) of noncystic noncavitary lesions. Patients with lesions associated with cystic airspaces and patients with noncystic noncavitary lesions showed no significant difference in frequencies of complication (all: 40% [36/90] vs 38% [68/180], p=.79; major: 4% [4/90] vs 6% [10/180], p=.78; minor: 36% [32/90] vs 32% [58/180], p=.59), frequency of nondiagnostic biopsies (12% [11/90] vs 9% [16/180], p=.40), or diagnostic performance (accuracy: 94.% [85/90] vs 97% [175/180], p=.50; sensitivity: 94% [76/81] vs 97% [160/165], p=.50; specificity: 100% [9/9] vs 100% [15/15]; p>.99), respectively. All false-negative results for malignancy in both groups occurred in patients with nondiagnostic CNB results. Among lesions associated with cystic airspaces that were resected after CNB (all malignant), the cystic airspaces most commonly represented tumor degeneration (22/31, 71%). Conclusion: CT-guided CNB is safe and accurate for assessing pulmonary lesions associated with cystic airspaces. Clinical Impact: CNB may help avoid a missed or delayed cancer diagnosis in pulmonary lesions with cystic airspaces.

Despite extensive research, open questions about the biological underpinnings of Alzheimer’s disease (AD) remain. Neuroimaging biomarkers based on positron emission tomography (PET) and magnetic resonance imaging (MRI) offer in vivo insights into these complex biological changes and interactions. However, most evidence to date comes from cross-sectional studies, limiting our understanding of disease progression. Longitudinal studies enable the investigation of biological changes within individuals, revealing how pathology evolves over time. With this review, we provide an overview of how longitudinal imaging biomarker studies have advanced the field and how they can contribute to future research. We highlight longitudinal biomarker studies that have provided critical insights into disease trajectories, staging, and individual variability. We further assess longitudinal multimodal studies which have elucidated interactions between AD-specific pathology, amyloid-β and tau, and broader biological changes like neurodegeneration, neuronal dysfunction, vascular disease, and inflammation. Further, we discuss associations of brain changes with symptomatology and clinical outcomes and conclude with challenges and future directions.