Correlation Between Apparent Diffusion Coefficient Values of the Renal Parenchyma and Estimated Glomerular Filtration Rates on 3-T Diffusion-Weighted Echo-Planar Magnetic Resonance Imaging

Fibrosis in Chronic Kidney Disease: Pathophysiology and Therapeutic Targets

Chronic kidney disease (CKD) is a slowly progressive condition characterized by decreased kidney function, tubular injury, oxidative stress, and inflammation. CKD is a leading global health burden that is asymptomatic in early stages but can ultimately cause kidney failure. Its etiology is complex and involves dysregulated signaling pathways that lead to fibrosis. Transforming growth factor (TGF)-β is a central mediator in promoting transdifferentiation of polarized renal tubular epithelial cells into mesenchymal cells, resulting in irreversible kidney injury. While current therapies are limited, the search for more effective diagnostic and treatment modalities is intensive. Although biopsy with histology is the most accurate method of diagnosis and staging, imaging techniques such as diffusion-weighted magnetic resonance imaging and shear wave elastography ultrasound are less invasive ways to stage fibrosis. Current therapies such as renin-angiotensin blockers, mineralocorticoid receptor antagonists, and sodium/glucose cotransporter 2 inhibitors aim to delay progression. Newer antifibrotic agents that suppress the downstream inflammatory mediators involved in the fibrotic process are in clinical trials, and potential therapeutic targets that interfere with TGF-β signaling are being explored. Small interfering RNAs and stem cell-based therapeutics are also being evaluated. Further research and clinical studies are necessary in order to avoid dialysis and kidney transplantation.

Multiparametric quantitative renal MRI in children and young adults: comparison between healthy individuals and patients with chronic kidney disease

PURPOSE

Multiparametric quantitative renal MRI may provide noninvasive radiologic biomarkers of chronic kidney disease (CKD) based on investigations in animal models and adults. We aimed to (1) obtain normative multiparametric quantitative MRI data from the kidneys of healthy children and young adults, (2) compare MRI measurements between healthy control participants and patients with CKD, and (3) determine if MRI measurements correlate with clinical and laboratory data as well as histology.

METHODS

This was a prospective, case-control study of 20 healthy controls and 12 CKD patients who underwent percutaneous renal biopsy ranging from 12 to 23 years of age between October 2018 and March 2020. Kidney function was documented and pathology assessed for fibrosis/inflammation. Utilizing a field strength of 1.5T, we examined renal T1, T2, and T2* relaxation mapping, MR elastography (MRE), and diffusion-weighted imaging (DWI). A single analyst made all manual measurements for quantitative MRI pulse sequences. Independent measurements from cortex, medulla, and whole kidney were obtained by drawing regions of interest on single slices from the upper, mid, and lower kidney. A weighted average was calculated for each kidney; if two kidneys, the right and left were averaged. Continuous variables were compared with Mann-Whitney U test; bivariate relationships were assessed using Spearman rank-order correlation.

RESULTS

Median estimated glomerular filtration rate (eGFR) was 112.3 ml/min/1.73 m² in controls (n = 20, 10 females) and 55.0 ml/min/m² in CKD patients (n = 12, 2 females) (p < 0.0001). Whole kidney (1333 vs. 1291 ms; p = 0.018) and cortical (1212 vs 1137 ms; p < 0.0001) T1 values were higher in CKD patients. Cortical T1 values correlated with eGFR (rho = - 0.62; p = 0.0003) and cystatin C (rho = 0.58; p = 0.0007). Whole kidney (1.87 vs. 2.02 10^-3 mm²/s; p = 0.007), cortical (1.89 vs. 2.04 10^-3 mm²/s; p = 0.008), and medullary (1.87 vs. 1.98 10^-3 mm²/s; p = 0.0095) DWI apparent diffusion coefficients (ADC) were lower in CKD patients. Whole kidney ADC correlated with eGFR (rho = 0.45; p = 0.012) and cystatin C (rho = - 0.46; p = 0.009). Cortical histologic inflammation correlated with DWI ADC (rho = - 0.71; p = 0.011).

CONCLUSION

Renal T1 relaxation and DWI ADC measurements differ between pediatric healthy controls and CKD patients, correlate with laboratory markers of CKD, and may have histologic correlates.

Evaluation of renal fibrosis in various causes of glomerulonephritis by MR elastography: a clinicopathologic comparative analysis

BACKGROUND

Renal parenchymal fibrosis is the most important determinant of kidney disease progression and it is determined via biopsy. The aim of this study is to evaluate the renal stiffness noninvasively by magnetic resonance elastography (MRE) and to compare it with clinicopathologic parameters in glomerulonephritis and AA amyloidosis patients.

METHODS

Thirty-four patients with glomerular filtration rate (GFR) over 20 ml/min/1.73m² had non-contrast MRE prospectively. Kidney stiffness values were obtained from whole kidney, cortex, and medulla. Values were correlated with GFR, albuminuria, proteinuria, and degree of fibrosis that are assessed via renal biopsy. Patients were grouped clinicopathologically to assess the relation between stiffness and chronicity.

RESULTS

Mean whole kidney, cortex, and medulla stiffnesses were 3.78 (± 1.26), 3.63 (± 1.25), and 4.77 (± 2.03) kPa, respectively. Mean global glomerulosclerosis was 22% (± 18%) and median segmental glomerulosclerosis was 4% (min-max: 0%-100%). Extent of tubulointerstitial fibrosis was less than 25% in 26 of the patients (76.5%), 25%-50% in 6 of the patients (17.6%), and higher than 50% in 2 of the patients (5.9%). Fourteen patients were defined to have chronic renal parenchymal injury. MRE-derived stiffness values correlated negatively with parameters of fibrosis. Lower stiffness values were observed in patients with chronic renal injury compared to those without (P < 0.05 for whole kidney and medulla MRE-derived stiffness).

CONCLUSION

MRE-derived stiffness values were lower in patients with chronic injury. Stiffness decreases as glomerulosclerosis and tubulointerstitial fibrosis progresses in patients with primary glomerulonephritis and AA amyloidosis. With future studies, there may be a role for MRE to assess renal function in concert with conventional markers.