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Introduction: Ultrasound and colorDoppler technique, which is relatively inexpensive, rapid, non-invasive and repeatable is a powerful tool used for early diagnosis of vascular access (VA) complications in hemodialysis patients. To date a standard and widely comprehensible echocolorDoppler (ECD) protocol is not available. Materials and Methods: A simple step-by-step protocol based on anatomical and hemodynamic parameters of VA has been developed during a 3-years VA ECD follow-up. It consists of an ECD study scheme. The algorithm created involves the calculation of brachial artery flow, description of artero-venous and/or graft-vascular anastomosis and efferent vessel and/or graft. Results: The algorithm allows to formulate a medical report that takes into account both anatomic and hemodynamic parameters of the VA. Reduction of complications and the prevention of chronic complications as well as the early detection of acute problems were achieved. Discussion and Conclusion: The creation of a step-by-step protocol may simplify the multidisciplinary management of VA, its monitoring and the early diagnosis of its complications.

Acute cortical necrosis and hemolytic uremic syndrome (HUS) are 2 clinical scenarios of parenchymal acute kidney injury (AKI) related to renal microvascular injury. Acute cortical necrosis is a rare condition related to an ischemic necrosis of renal cortex. Necrotic lesions can be due to several injuries and may be focal, multifocal or diffuse. Renal necrotic lesions become visible with ultrasound only after renal recovery. HUS is a rare disease characterized by hemolytic anemia, thrombocytopenia and AKI. Color Doppler ultrasound is useful during diagnostic and follow-up phase. Renal artery thrombosis and renal vein thrombosis may also cause parenchymal AKI. Acute renal infarction is a rare pathological condition that occurs due to clots or cholesterol aggregates occluding renal artery or its branches. Several causes may lead to partial or massive kidney ischemic necrosis. Contrast-enhanced CT allows definitive diagnosis in 80% of cases and, at present, it is the first imaging technique used. Ultrasound (US) sensitivity and specificity significantly increases with color Doppler and contrast-enhanced US (CEUS). In AKI patients, in whom the use of iodinated contrast media is contraindicated, color Doppler and CEUS may be valid alternatives for the diagnosis of acute renal infarction. Renal vein thrombosis may be primary or secondary to retroperitoneal neoplasm or inflammatory diseases. It rarely causes an acute worsening of renal function because of the presence of several anastomosis that prevent parenchymal necrosis due to venous congestion. Color Doppler US could detect thrombus within the lumen and document the absence of venous flow.

Secondary nephropathies can be associated with disreactive immunological disorders or with a non-inflammatory glomerular damage. In systemic lupus erythematosus (SLE), scleroderma and rheumatoid arthritis as in other connective tissue diseases, kidney volume and cortex echogenicity are the parameters that best correlate with clinical severity of the disease, even if the morphological aspect is generally non-specific. Doppler studies in SLE document the correlation between resistance indexes (RIs) values and renal function. Acquired immunodeficiency syndrome (HIV) causes different types of renal damage. At ultrasound (US), kidneys have almost a normal volume, while during superinfection they enlarge (coronal diameter >13 cm) and become globular, loosing their normal aspect. Cortex appears highly hyperechoic, uniform or patchy. Microcalcifications of renal cortex and medulla are a US sign that can suggest HIV. In amyloidosis, kidneys appear normal or increased in volume in the early stages of disease. Renal cortex is diffusely hyperechoic and pyramids can show normal size and morphology, but more often they appear poorly defined and hyperechoic. RIs are very high since the early stages of the disease. Nephromegaly with normal kidney shape is the first sign of lymphoma or multiple myeloma. In systemic vasculitis, renal cortex is diffusely hyperechoic, while pyramids appear hypoechoic and globular due to interstitial edema. When vasculitis determines advanced chronic kidney disease stages, kidneys show no specific signs. Microcirculation damage is highlighted by increased RIs values >0.70 in the chronic phase.

Acute tubular necrosis (ATN) is the most common type of acute kidney injury (AKI) related to parenchymal damage (90% of cases). It may be due to a direct kidney injury, such as sepsis, drugs, toxins, contrast media, hemoglobinuria and myoglobinuria, or it may be the consequence of a prolonged systemic ischemic injury. Conventional ultrasound (US) shows enlarged kidneys with hypoechoic pyramids. Increased volume is largely sustained by the increase of anteroposterior diameter, while longitudinal axis usually maintains its normal length. Despite the role of color Doppler in AKI still being debated, many studies demonstrate that renal resistive indexes (RIs) vary on the basis of primary disease. Moreover, several studies assessed that higher RI values are predictive of persistent AKI. Nevertheless, due to the marked heterogeneity among the studies, further investigations focused on timing of RI measurement and test performances are needed. Acute interstitial nephritis is also a frequent cause of AKI, mainly due to non-steroidal anti-inflammatory drugs and antibiotics administration. The development of acute interstitial nephritis is due to an immunological reaction against nephritogenic exogenous antigens, processed by tubular cells. In acute interstitial nephritis, as well as in ATN, conventional US does not allow a definitive diagnosis. Kidneys appear enlarged and widely hyperechoic due to interstitial edema and inflammatory infiltration. Also, in this condition, hemodynamic changes are closely correlated to the severity and the progression of the anatomical damage.

Vascular chronic diseases represent one of the leading causes of end-stage renal disease in incident dialysis patients. B-Mode ultrasound (US) and color Doppler (CD) have a high sensitivity and specificity in the diagnosis of vascular chronic diseases. US and CD should be used to identify subjects in the high risk population who are affected by main renal artery stenosis (RAS) and to identify and characterize patients without RAS who have chronic ischemic nephropathy caused by nephroangiosclerosis and/or atheroembolic disease. The most important CD parameters in the work-up of suspected RAS are increased peak systolic velocity and diastolic velocity, spectral broadening, high renal:aortic ratio and lateralization of renal resistive indexes (RIs). In the absence of direct or indirect signs of RAS, increases in intraparenchymal RIs, associated with systemic atherosclerotic disease, are indicative of microcirculation damage related to nephroangiosclerosis or atheroembolic 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

Acquired cystic kidney disease (ACKD) and renal cell carcinoma (RCC) are the most important manifestations of end-stage kidneys' structural changes. ACKD is caused by kidney damage or scarring and it is characterized by the presence of small, multiple cortical and medullary cysts filled with a fluid similar to preurine. ACKD prevalence varies according to predialysis and dialysis age and its pathogenesis is unknown, although it is stated that progressive destruction of renal tissue induces hypertrophy/compensatory hyperplasia of residual nephrons and may trigger the degenerative process. ACKD is almost asymptomatic, but it can lead to several complications (bleeding, rupture, infections, RCC). Ultrasound (US) is the first level imaging technique in ACKD, because of its sensitivity and reliability. The most serious complication of ACKD is RCC, which is stimulated by the same growth factors and proto-oncogenes that lead to the genesis of cysts. Two different histological types of RCC have been identified: (1) RCC associated with ACKD and (2) papillary renal clear cell carcinoma. Tumors in end-stage kidneys are mainly small, multifocal and bilateral, with a papillary structure and a low degree of malignancy. At US, RCC appears as a small inhomogeneous nodule (

Kidneys' imaging provides useful information in acute kidney injury (AKI) diagnosis and management. Today, several imaging techniques give information on kidneys anatomy, urinary obstruction, differential diagnosis between AKI and chronic kidney disease (CKD), renal blood flow and glomerular filtration rate. Ultrasound is a safe, non-invasive and repeatable imaging technique so it is widely used in the first level work-up of AKI. The utility of contrast-enhanced computed tomography and magnetic resonance imaging in AKI or in AKI during CKD is limited because of renal toxicity associated with contrast agents used.

Chronic tubulointerstitial diseases are a common final pathway toward chronic renal failure regardless the primary damage (glomerular, vascular or directly the tubulointerstitium). Chronic tubulointerstitial nephritis (CTN) is characterized by interstitial scarring, fibrosis and tubule atrophy, resulting in progressive chronic kidney disease. Most frequent causes of CTN are drugs, heavy metals, obstructive uropathy, nephrolithiasis, reflux disease, immunologic diseases, neoplasia, ischemia, metabolic diseases, genetics and miscellaneous. At ultrasound (US), kidneys' morphological aspect is similar in all forms of chronic interstitial nephropathy and only chronic pyelonephritis with or without reflux shows distinguishing characteristics. In interstitial nephropathy, kidneys' profiles are finely irregular and corticomedullary differentiation is altered because of a diffused hyperechogenicity. The only indirect sign of chronic interstitial damage can be derived from the value of intrarenal resistive indexes that hardly overcome 0.75. US is mandatory in clinical chronic pyelonephritis work-up because it provides information on kidney's diameter and on growth nomogram in children. Renal profiles can be more or less altered depending on the number of cortical scars and the presence of pseudonodular areas of segmental compensatory hypertrophy. In the early stages, US diagnosis of renal tuberculosis is difficult because parenchymal lesions are non-specific. US sensitivity in the diagnosis of hydronephrosis is very high, close to 100% and, finally, US is the first choice imaging technique in the diagnosis of urinary lithiasis.

Approximately 70% of community-acquired cases of acute kidney injury are attributed to pre-renal causes. In most of these cases, the underlying kidney function may be normal, but decreased renal perfusion associated with low intravascular volume or decreased arterial pressure can determine a reduced glomerular filtration rate (GFR). Autoregulatory mechanisms can partially compensate renal perfusion reduction in order to maintain GFR. In patients with pre-existing chronic kidney disease, however, these mechanisms are impaired, and the susceptibility to develop acute-on-chronic renal failure is higher.

Renal failure commonly occurs in patients affected by cirrhosis, especially when there is ascites. It is typically secondary to intercurrent events that can further compromise blood flow in conditions of relatively decreased renal perfusion. Hepatorenal syndrome (HRS) is a particular and common type of kidney failure that affects patients with liver cirrhosis or, less frequently, with fulminant hepatic failure. The syndrome is characterized by splanchnic vasodilation and renal vasoconstriction. The classification of HRS identifies 2 categories of kidney failure, known as type 1 and type 2 HRS, that occur in patients with either cirrhosis or fulminant hepatic failure.

Acute kidney injury (AKI), also known in the past as acute renal failure, is a syndrome characterized by the rapid loss of kidney excretory function. It is usually diagnosed by the accumulation of end products of nitrogen metabolism (urea and creatinine) or decreased urine output or both. AKI is the clinical consequence of several disorders that acutely affect the kidney, causing electrolytes and acid-base imbalance, hyperhydration and loss of depurative function. AKI is common in critical care patients in whom it is often secondary to extrarenal events. No specific therapies can attenuate AKI or accelerate renal function recovery; thus, the only treatment is supportive. New diagnostic techniques such as renal biomarkers might improve early diagnosis. Also ultrasonography helps nephrologists in AKI diagnosis, in order to describe and follow kidney alterations and find possible causes of AKI. Renal replacement therapy is a life-saving treatment if AKI is severe. If patients survive to AKI, and did not have previous chronic kidney disease (CKD), they typically recover to dialysis independence. However, evidence suggests that patients who have had AKI are at increased risk of subsequent CKD.

Cysts are frequently found in chronic kidney disease (CKD) and they have a different prognostic significance depending on the clinical context. Simple solitary parenchymal cysts and peripelvic cysts are very common and they have no clinical significance. At US, simple cyst appears as a round anechoic pouch with regular and thin profiles. On the other hand, hereditary polycystic disease is a frequent cause of CKD in children and adults. Autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are the best known cystic hereditary diseases. ADPKD and ARPKD show a diffused cystic degeneration with cysts of different diameters derived from tubular epithelium. Medullary cystic disease may be associated with tubular defects, acidosis and lithiasis and can lead to CKD. Acquired cystic kidney disease, finally, is secondary to progressive structural end-stage kidney remodelling and may be associated with renal cell carcinoma.

In diabetes, kidneys' morphological changes are non-specific at ultrasound (US) and they vary according to disease stage. In the earlier stages, kidneys are enlarged and diffusely hypoechoic due to hyperfiltration. Kidneys size decreases only in advanced stages whereas renal cortical echogenicity progressively increases due to glomerulosclerosis. Nephromegaly, as well as discrepancy between size and renal function, are typical features of diabetic nephropathy either in early or in advanced stages of the disease. Resistive indexes progressively increase together with serum creatinine levels and macro/microcirculation damage. Chronic glomerulonephritis (CGN) is the third leading cause of chronic kidney disease and it represents the clinical evolution of a variety of primary or secondary glomerular diseases. Kidneys in CGN are gradually reduced in volume, but remain symmetric, easily recognizable in renal space until the disease's later stages.

Renal failure commonly occurs in patients affected by cirrhosis, especially when there is ascites. It is typically secondary to intercurrent events that can further compromise blood flow in conditions of relatively decreased renal perfusion. Hepatorenal syndrome (HRS) is a particular and common type of kidney failure that affects patients with liver cirrhosis or, less frequently, with fulminant hepatic failure. The syndrome is characterized by splanchnic vasodilation and renal vasoconstriction. The classification of HRS identifies 2 categories of kidney failure, known as type 1 and type 2 HRS, that occur in patients with either cirrhosis or fulminant hepatic failure.

Serum oxalic acid (sOx) was determined with a new, specific enzymatic method in 73 uremic patients and the values were plotted against serum creatinine. 41 patients received a free mixed diet, and 32 similar patients were given a low-nitrogen diet supplemented with essential amino acids, ketoanalogues, and calcium carbonate (AD). A significant correlation was found between serum creatinine and sOx levels in patients following a free mixed diet, while no correlation appeared in patients on AD: The sOx concentrations were significantly lower and even normal in this group, and a significant reduction of sOx occurred in 10 patients with chronic renal failure, who changed from a free mixed diet to the AD. The lowering of sOx concentration in patients following AD is attributed both to low intake of its metabolic precursors and to the oral calcium carbonate supplementation.