Table 18-5 summarizes a checklist approach to the ultrasound examination. In cases of unilateral obstruction with acute renal failure, sonographic evaluation may show evidence of chronic renal parenchymal disease in the unobstructed kidney. Table 18-6 lists the most common causes of bilateral smooth renal atrophy. 18-18). However, T1-weighted images provide good corticomedullary differentiation. Each end of the kidney is commonly called a pole. The kidneys are a pair of bean-shaped organs located below the rib cage, one on each side of the spine. Obstruction can cause renal failure if it is bilateral (Box 18-3) or if there is preexisting disease in the unobstructed kidney. If the renal pelvis extends out of the renal sinus, it is considered to be an. Radiologists divide the kidney into three parts: the upper pole, lower pole, and the interpole (whi. In fact, evaluation of the renal collecting system during the excretory phase often requires window and level settings approaching those used for evaluating the osseous structures (Fig. Their shape resembles a bean, where we can describe the superior and inferior poles, as well as the major convexity pointed laterally, and the minor concavity pointed medially. The main unit of the medulla is the renal pyramid. The urinary system comprises the upper urinary tracts (kidneys and ureters), the urinary bladder, and the urethra. Note origin of inferior accessories near inferior poles on each side. Figure 18-20 Axial image from unenhanced computed tomography of the kidneys performed 2 days after an angiographic procedure demonstrates stasis of contrast in the renal cortex, resulting in a persistent corticomedullary phase of enhancement. Extraaortic origin of the renal arteries and accessory renal arteries are common. The ureters are the tubes that carry urine from the renal pelvis to the bladder. If this appearance were present bilaterally, chronic renal disease such as chronic glomerulonephritis would be a more likely explanation. Note origin of inferior accessories near inferior poles on each side. Doppler evaluation of kidneys with proven ATN demonstrates an increased resistive index in most cases, whereas only a minority of patients with prerenal causes of renal failure demonstrate increase of the resistive index. Furthermore, since the left renal vein passes between the superior mesenteric artery and the abdominal aorta, an enlargement of the superior mesenteric artery can compress the left renalvein and cause an obstruction of drainage from all three structures that use the left renal vein for drainage (left suprarenal gland, left kidney, and left testicle). The fused kidneys can have a variety of orientations, including side by side, in-line, or perpendicular. Renal cysts become fairly common as people age and usually do not cause symptoms or harm. The nephrons within the cortex comprise some of the most highly perfused parenchymal tissue in the body. When echogenicity of the renal cortex equals that of the liver, renal function is abnormal in approximately 38% of cases. Advantages of scintigraphy include accurate quantitative measurement of function. BOX 18-3 Causes of Bilateral Hydronephrosis. If the renal pelvis extends out of the renal sinus, it is considered to be an extrarenal pelvis (Fig. In addition to the renal artery, accessory renal arteries are present too. "Angio" indicates blood vessels, "myo" indicates muscle, and "lipoma" indicates fat. The cortex of a normal kidney is usually less echogenic than the adjacent normal liver. Read More Created for people with ongoing healthcare needs but benefits everyone. Read more. In this region, the anterior and posterior hilar lip is identified (Fig. The anteromedial, aspect of the interpolar region is interrupted by the renal hilum to make a C shape. 18-7). There are 8-18 renal pyramids in each kidney, that on the coronal section look like triangles lined next to each other with their bases directed toward the cortex and apex to the hilum. Let's see what is nephron and how it is structured,so you can remember it for good. 18-26). Figure 18-18 Single-detector computed tomographic images from ureteropelvic junction deformity in the right side of a horseshoe kidney. Note that there is no contrast in the aorta. On the superior aspect of each kidney is the adrenal gland. When multiple clefts in the renal cortex are present throughout the kidney, it is described as fetal lobulation. Localized means that the tumor has not spread out from where it first started. In adults, the normal kidney is 10-14 cm long in males and 9-13 cm long in females, 3-5 cm wide, 3 cm in antero-posterior thickness and weighs 150-260 g. The left kidney is usually slightly larger than the right. 18-28). Axial maximum intensity projection image from the arterial phase of a contrast-enhanced computed tomographic scan from a prospective renal donor demonstrates early prehilar branching of the left renal artery. Curated learning paths created by our anatomy experts, 1000s of high quality anatomy illustrations and articles. Kenhub. The presence of significant renal parenchyma may justify surgical repair to maximize the functional contribution of that kidney. Log In or, Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on Google+ (Opens in new window), Estimated Creatinine Clearance and Glomerular Filtration Rate, Cockroft and Gault Equation for Calculating Estimated Creatinine Clearance, The Modification of Diet in Renal Disease (MDRD) is another method for estimating renal function that yields a value often called, The kidneys can be divided into three main regions from cranial to caudal. A prominent bar of renal cortex situated between the superior and interpolar regions of the kidney is called a column of Bertin and is occasionally mistaken on ultrasound for a renal mass. The visible contrast seen in the excretory phase has been concentrated many-fold. Sagittal ultrasound image of the left kidney demonstrates a unilateral small, smooth, echogenic kidney in a patient with renal artery stenosis. Renal size and cortical thickness can be assessed in a manner similar to ultrasound. Kidney stones are most often treated by ultrasound shock therapy, during which high-frequency radio waves break the stone into smaller pieces that can be passed naturally into the urine. While migrating superiorly, the kidneys rotate medially along their long axes and the inferior supplying mesonephric arteries degenerate. As the lobules of metanephric blastema coalesce to form each kidney, they do not always result in a smooth, uniform band of cortex. Each kidney should always be evaluated in long axis (coronal, sagittal, or both, depending on sonographic window) and axial to the kidney. Blood supply is variable and often includes extraaortic and multiple vessel origins. Look for retroaortic or circumaortic left renal vein. The renal corpuscle has two components: the glomerular (Bowmans) capsule in which sits the glomerulus. Urine that is concentrated in the renal papilla is subsequently excreted into a lumen lined with transitional epithelium. These are chronic processes that lead to a loss of renal cortex gradually and uniformly. Size disparity greater than 1.5 cm between kidneys should raise suspicion that one kidney is abnormal. 18-3). urinary system quizzes and labeled diagrams. Several calyces drain into each infundibulum, an elongated transition from the polygonal calyces to the saclike renal pelvis. The upper pelvis is the most common ectopic location for the kidney; most cases are also associated with abnormalities of rotation. Lets start with the right kidney anterior surface. Some forms of congenital UPJ obstruction are now treated with transureteroscopic endopyelotomy in which an incision is made from within the ureter using a ureteroscope. For most of the students, the nephron is a mystical complexed structure that may be hard to understand. The anterior surface faces towards the anterior abdominal wall, whereas the posterior surface is facing the posterior abdominal wall. Figure 18-19 Sagittal ultrasound image of the right kidney demonstrates increased size and echogenicity of the kidney, findings typical of human immunodeficiency virus nephropathy. IVC, Inferior vena cava. Chronic glomerulonephritis usually causes bilateral increased renal echogenicity with smooth atrophy, whereas renal artery stenosis usually causes a similar but unilateral appearance (Fig. This refers to the forming of the stones within the system of calyces because of too much calcium or uric acid into the filtrate. BOX 18-2 Crossing Vessels in Ureteropelvic Junction Obstruction. Note diameter of arteries because small accessory arteries may be sacrificed in many cases. Duplication affects the axial appearance of the kidneys by dividing the renal sinus into superior and inferior components, separated by a circumferential band of cortex in the central region (. In most kidneys, the renal hilum faces more anteromedial in the upper half of the kidney and more directly medial in the lower half. Some of them are congenital, such as a third kidney, which is usually atrophic. Always include unenhanced computed tomographic images to look for renal stones. Each nephron contains a renal corpuscle, which is the initial component that filters the blood, and a renal tubule that processes and carries the filtered fluid to the system of calyces. It's not clear what causes simple kidney cysts. Many clinical laboratories now provide computer-generated calculations of estimated creatinine clearance or eGFR using patient data in the medical information system. The renal cortex and medulla both have high signal intensity on T2-weighted images resulting in poor corticomedullary differentiation. At one end of each nephron, in the cortex of the kidney, is a cup-shaped structure called the Bowman's capsule. Because repeat imaging does not expose the patient to additional radiation, multiple phases including delayed images may be obtained and allow the creation of quantitative curves that define the initial filling and then clearing of dilated collecting system structures. The normal appearance of the calyx is created by the impression of the renal papilla. impression is preserved. 18-4). Chronic glomerulonephritis usually causes bilateral increased renal echogenicity with smooth atrophy, whereas renal artery stenosis usually causes a similar but unilateral appearance (Fig. An acute change in renal cortical echogenicity is occasionally seen with pyelonehritis. Hypotension is a stimulus for the kidneys to increase the retention of fluid and thus increase blood pressure. B, Low-attenuation lesion in the late nephrographic/early excretory phase is less suspicious in appearance. Hydronephrosis is important to detect, because obstructive uropathy is often reversible if identified early. However, T1-weighted images provide good corticomedullary differentiation. Supernumerary kidneys are quite rare and have been associated with aortic coarctation, vaginal atresia, and urethral duplications. But here is a neat little mnemonic to help. Of course, if the situation is the other way around (less than 5 liters of blood), blood pressure is too low (hypotension). It doesn't have to be that way. However, sometimes ureteroscopy is required to confirm the diagnosis in patients with hematuria. Imaging must provide detailed images of the renal parenchyma and a survey of arterial, venous, and ureteral anatomy. Renal size can be measured in several ways. Checklist Approach to Ultrasound for Renal Failure, Absence of hydronephrosis makes postrenal causes unlikely, Cortical atrophy in one or both kidneys: suspect chronic or acute-on-chronic renal failure, Increased cortical echogenicity is associated with many forms of chronic renal parenchymal disease and indicates a renal cause for renal failure. The glomerular membrane is designed in a way in which it is not permeable for big and important molecules in blood, such as plasma proteins, but it is permeable to the smaller substances such as sodium, potassium, amino acids and many others. The Modification of Diet in Renal Disease (MDRD) is another method for estimating renal function that yields a value often called estimated glomerular filtration rate (eGFR). 18-16). 18-6). Solid masses are more likely to be cancerous but they are not all cancerous. Table 18-7 lists causes of unilateral smooth renal atrophy. 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