Acute and Chronic Kidney Disease (CKD) are still important causes of morbi-mortality. Due to important limitations of laboratorial markers like microalbuminuria and serum creatinine, other techniques have been studied over the last decades. We provide a pictorial review with MR images from our institution, depicting the Diffusion-weighted imaging (DWI) features of acute kidney disease (including Acute Pyelonephritis (APN), hydronephrosis, abscesses, hematomas and sediment) and CKD. DWI assesses restriction to water molecules diffusion, as well as blood microcirculation and tubular flow, being a promising biomarker of the renal microstructure. Changes on renal perfusion, glomerular and tubular flow can thus modify both renal DWI signal and Apparent Diffusion Coefficient (ADC). APN, CKD, and obstruction typically exhibit restriction to water diffusion, with corresponding low cortical ADC values. Hematomas, abscesses and sediment also exhibit restriction and tend to appear particularly bright at high b values. In the set of acute infection, the lack of ionizing radiation makes DWI very attractive during pregnancy and childhood. Also, Diffusion Tensor Imaging (DTI), by measuring fractional anisotropy, provides an even better characterization of the renal microstructure, particularly in CKD, being able to depict alterations earlier than conventional blood biomarkers. After adequate standardization of these sequences, still under investigation, the need for biopsy and contrast administration can be obviated, highlighting DWI not only as a diagnostic tool but also as way to follow-up and guide treatment decisions. The importance of DWI goes well beyond tumor detection, particularly in the kidney. It is an increasingly recognized biomarker of renal function and fibrosis, namely in CKD. The role of DWI in APN and obstruction has also been explored and its imaging findings should figure in the checklist of the urogenital radiologist.
