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. 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 (. If the renal pelvis extends out of the renal sinus, it is considered to be an extrarenal pelvis (Fig. Since they are located deep retroperitoneally, the easiest way to examine them is from the patients back. Ultrasound permits real-time optimization of imaging relative to the axis of each kidney. The kidneys are bilateral organs placed retroperitoneally in the upper left and right abdominal quadrants and are part of the urinary system. The presence of significant renal parenchyma may justify surgical repair to maximize the functional contribution of that kidney. The normal appearance of the calyx is created by the impression of the renal papilla. Each segmental branch of the renal artery divides into multiple interlobar arteries that course along the periphery of the medullary pyramids and causes small interlobular branches (Fig. The cortex of a normal kidney is usually less echogenic than the adjacent normal liver. Kidneys are located just below your ribcage and behind your belly. Technetium 99m dimercaptosuccinic acid (DMSA) and glucoheptonate (GHA) are both used for evaluation of renal parenchyma. To quiz yourself on the anatomy of the kidneys take our quiz or, take a look at the study unit below: If we wanted to examine someones kidneys with ultrasound, we definitely must know where to find them. Static-fluid (T2-weighted) MR urography and phase-contrast MR angiography are useful techniques that do not require intravenous contrast material. The renal pelvis then tapers like a funnel to join the ureter. Chronic glomerulonephritis usually causes bilateral increased renal echogenicity with smooth atrophy, whereas renal artery stenosis usually causes a similar but unilateral appearance (Fig. 18-4). Jana Vaskovi MD Coronal reformation from contrast-enhanced computed tomography performed for renal donation demonstrates a retroaortic left renal vein crossing the aorta well inferior to the level of the renal hila. 18-15). Reading time: 23 minutes. 18-13). A furosemide challenge is often administered after initial excretion is observed to measure the impact of diuresis on the clearance of radiotracer from the renal pelvis. Look for retroaortic or circumaortic left renal vein. Technetium 99m-mercaptoacetyltriglycin (MAG3) is excreted by the kidneys (mainly through secretion by proximal tubules) and provides evaluation of renal function, particularly in cases of suspected obstruction. More tenuous vascular supply to the renal medulla makes it more susceptible to ischemia. Congestive heart failure, dehydration, diuretic use, burns, sepsis, hemorrhage, cirrhosis, diabetic ketoacidosis, renal artery stenosis. For most of the students, the nephron is a mystical complexed structure that may be hard to understand. But more often, kidney cysts are a type called simple kidney cysts. Some centers use diuretics or fluid bolus, or both, during CT urography to dilute the excreted contrast to improve assessment of the urothelium. Axial images of the left kidney from a three-phase renal computed tomographic scan demonstrate improved conspicuity of low-attenuation lesions of the renal medulla during the nephrographic phase. The left kidney (not shown) had a similar appearance. The segmental arteries then branch into the interlobar arteries, which further branch into the arcuate arteries. Most radiologists consider 10 to 12 cm to be an approximate reference range for renal length in adults, allowing for an additional 1 cm in either direction for patients at the extremes of height. C, More severe hydronephrosis results in more pronounced shortening of the papilla. This plexus provides input from: The sensory nerves from the kidney travel to the spinal cord at the levels T10-T11, which is why the pain in the flank region always rises suspicions that something is wrong with the corresponding kidney. 18-1). Other malfunctions of the kidney are presented through acute kidney failure, a serious and urgent medical condition. Each end of the kidney is commonly called a pole. If, however, a vessel crosses the UPJ at the level of obstruction, a blind incision made from the inside of the ureteral lumen can result in severe hemorrhage. Causes. B, A curved planar reformation of the crossing vein demonstrates its course. In order to understand the functions of the kidney, we must first learn its anatomy. Figure 18-18 Single-detector computed tomographic images from ureteropelvic junction deformity in the right side of a horseshoe kidney. 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 ureters are the tubes that carry urine from the renal pelvis to the bladder. The portion of the kidney between the poles is called the interpolar region and contains the renal hilum (Fig. The defect is the extension of sinus fat into the cortex, usually at the border of the upper pole and interpolar region of the kidney. In other cases, each renal unit has its own ureter. It is also permeable for the products of the metabolism, such are creatinine and drug metabolites. Note origin of inferior accessories near inferior poles on each side. It's not clear what causes simple kidney cysts. 18-6). The posterior branch supplies the posterior part of the kidney, whereas the anterior branch arborizes into five segmental arteries, each supplying a different renal segment. The most common indication for cortical scintigraphy is to evaluate kidneys that have been injured by vesicoureteral reflux, chronic obstruction, or severe or repeated urinary infections. Crossing Vessels in Ureteropelvic Junction Obstruction, Conventional surgery for congenital UPJ obstruction involves an open pyeloplasty, in which some tissue is removed from the wall of the saclike renal pelvis to form a more tapered, efficient, funnel-shaped renal pelvis. Read More Created for people with ongoing healthcare needs but benefits everyone. Normal parenchymal enhancement on CT or MRI allows definitive characterization. Figure 18-12 Axial sections of the right kidney from contrast-enhanced computed tomography demonstrate a bar of renal parenchyma separating renal hila in the superior and inferior poles, consistent with duplication. 18-19). The presence of significant renal parenchyma may justify surgical repair to maximize the functional contribution of that kidney. The kidneys are highly vascular (contain a lot of blood vessels) and are divided into three main regions: the renal cortex (outer region which contains about 1.25 million renal tubules), renal medulla (middle region which acts as a collecting chamber), and renal pelvis (inner region which receives urine through the major calyces). The visible contrast seen in the excretory phase has been concentrated many-fold. When abnormal echogenicity is detected, it is important to note whether it is unilateral or bilateral. A, Tips of the fornices are sharply defined. All content published on Kenhub is reviewed by medical and anatomy experts. Figure 18-9 Coronal computed tomographic image in the corticomedullary phase shows normal corticomedullary differentiation along the lobulated contour, consistent with fetal lobulation. However, this individual is more likely to show a decline in renal function from an additional insult. Learn more about the anatomy of the kidneys and the urinary system with our urinary system quizzes and labeled diagrams. Unlike the excretory phase of enhanced CT, signal intensity within the renal collecting systems is reduced on T1- and T2-weighted MR images once excreted gadolinium-based contrast media becomes sufficiently concentrated. A junctional cortical line is a common septum of capsule typically seen on ultrasound as an echogenic line at the site of fusion between the superior pole and middle third of the kidney (Fig. The parenchyma of the kidney consists of the outer renal cortex, and inner renal medulla. Although each kidney is about the size of a fist, the approximately one million nephrons per kidney require nearly 20% of the total cardiac output to perform this multitude of functions. Lets start with the right kidney anterior surface. Increasing pressure within the lumen initially distends the fornices (acutely angled portions of the calyx along the sides of the papillae), whereas the central portion of the papillary impression is preserved. D, If pressure on the papilla persists, the ischemic papilla undergoes necrosis, allowing the calyx to protrude outward toward the cortex. Figure 18-23 Axial image of the left kidney obtained in the excretory phase of a computed tomographic urogram demonstrates the effects of window settings on visualizing structures near excreted contrast. Register now Conventional surgery for congenital UPJ obstruction involves an open pyeloplasty, in which some tissue is removed from the wall of the saclike renal pelvis to form a more tapered, efficient, funnel-shaped renal pelvis. The bilateral small smooth kidney pattern describes most of what is often diagnosed on sonography as medical renal disease, although the authors prefer the term renal parenchymal disease. Because of this, the tubules are designed in a way that they reabsorb the necessary substances, (sodium, potassium, and amino acids as mentioned before) and carries them back to the blood; whereas they do not absorb but rather secrete unnecessary substances such as creatinine and drug metabolites for excretion from the body. Box 18-2 provides some tips regarding crossing vessels in UPJ obstruction. Advantages of scintigraphy include accurate quantitative measurement of function and parenchymal mass without the risks for nephrotoxicity associated with iodinated contrast media or nephrogenic systemic fibrosis associated with gadolinium contrast agents. The left artery has a short way to the left kidney, whereas the right has to go behind the inferior vena cava in order to reach the right kidney. Figure 18-14 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. In this case, the right kidney had more favorable anatomy for laparoscopic donor nephrectomy. 18-4). Calcifications and renal calculi are notoriously poorly demonstrated with MRI. 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). It participates in vital processes such as regulation of blood osmolarity and pH, regulation of blood volume and blood pressure, production of hormones, and filtration of foreign substances. AMLs can bleed and while not cancerous are still taken very seriously. The renal veins empty to the inferior vena cava, so the right vein is shorter because the inferior vena cava runs closer to the right kidney. Despite different methods of accumulation, each is sequestered by the renal cortex, providing an opportunity to quantify the volume of renal parenchymal tissue in each kidney. The anterior surface of the left kidney, has the following anatomical relations: The posterior surfaces of both kidneys are related to certain neurovascular structures and muscles: You can easily remember these with the mnemonic: 1-2-3-4 All Boys Need Muscle. Figure 18-25 Sagittal ultrasound image of the left kidney demonstrates a unilateral small, smooth, echogenic kidney in a patient with renal artery stenosis. B, Mild hydronephrosis results in rounding of the fornices with mild shortening of the papillary impression. Unlike the excretory phase of enhanced CT, signal intensity within the renal collecting systems is reduced on T1- and T2-weighted MR images once excreted gadolinium-based contrast media becomes sufficiently concentrated. The calcium or uric acid will precipitate and form stones. It can be caused by a variety of factors, but most often arises because of the ischemia of the kidney and the toxic effect of some medications, resulting in the failure of all kidney functions. Eliminating toxic metabolites through urine, regulation of blood homeostasis and blood pressure, production of some hormones, Positioned retroperitoneally, consists of the cortex and medulla, empties urine into the ureter (which carries urine to the urinary bladder), Renal artery (branch of the abdominal aorta), Renal vein (drains to the inferior vena cava), Third kidney, horseshoe kidney, kidney agenesis, kidney stones, acute kidney failure, Regulates the amount of fluid in the body by increasing or decreasing the urine production, Maintain the pH of blood at 7.4 by decreasing or increasing the excretion of hydrogen ions, Medial part of the lower half of superior pole, Lateral part of the lower half of superior pole, Lateral part of inferior half of anterior surface, Medial part of inferior half of anterior surface, The perinephric fat (perirenal fat capsule). chronic obstruction, or severe or repeated urinary infections. Dialysis. The renal cortex is part of your kidney, which itself is part of the urinary tract. IVC, Inferior vena cava. Obstruction can cause renal failure if it is bilateral (Box 18-3) or if there is preexisting disease in the unobstructed kidney. The initiation is caused by the increase in volume that stretches the walls of the calyces. Urine that is concentrated in the renal papilla is subsequently excreted into a lumen lined with transitional epithelium. Retrograde urogram shows a calculus in the left ureter. A, Steady-state free precession, (B) T2-weighted with fat saturation, (C) T1-weighted, (D) T1-weighted with fat saturation, (E) postcontrast corticomedullary phase, and (F) postcontrast nephrographic phase. It is notable that the kidney has a very rich blood supply. Obstruction can cause renal failure if it is bilateral (Box 18-3) or if there is preexisting disease in the unobstructed kidney. 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