Imaging in Chronic Kidney Disease.

Chronic kidney disease (CKD) diagnosis and staging are based on estimated or calculated glomerular filtration rate (GFR), urinalysis and kidney structure at renal imaging techniques. Ultrasound (US) has a key role in evaluating both morphological changes (by means of B-Mode) and patterns of vascularization (by means of color-Doppler and contrast-enhanced US), thus contributing to CKD diagnosis and to the follow-up of its progression. In CKD, conventional US allows measuring longitudinal diameter and cortical thickness and evaluating renal echogenicity and urinary tract status. Maximum renal length is usually considered a morphological marker of CKD, as it decreases contemporarily to GFR, and should be systematically recorded in US reports. More recently, it has been found to be a significant correlation of both renal longitudinal diameter and cortical thickness with renal function. Conventional US should be integrated by color Doppler, which shows parenchymal perfusion and patency of veins and arteries, and by spectral Doppler, which is crucial for the diagnosis of renal artery stenosis and provides important information about intrarenal microcirculation. Different values of renal resistive indexes (RIs) have been associated with different primary diseases, as they reflect vascular compliance. Since RIs significantly correlate with renal function, they have been proposed to be independent risk factors for CKD progression, besides proteinuria, low GFR and arterial hypertension. Despite several new applications, US and color Doppler contribute to a definite diagnosis in <50% of cases of CKD, because of the lack of specific US patterns, especially in cases of advanced CKD. However, US is useful to evaluate CKD progression and to screen patients at risk for CKD. The indications and the recommended frequency of color Doppler US could differ in each case and the follow-up should be tailored.