Learn how we can help 1.2k views Reviewed Dec 09, 2022 Thank This is why the kidney is essential for the circulatory hemostasis. Other common kidney conditions are acquired through life, and one of the most common is nephrolithiasis (kidney stones). 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. Table 18-3 Utility of Different Phases of Renal Contrast Enhancement. Look carefully for accessory arteries at upper and lower poles (Fig. The muscular relations of the inferior half are easy to remember by dividing the kidney surface into three vertical stripes, where the medial stripe represents the impression of the psoas major muscle, the central stripe the quadratus lumborum, and the lateral stripe the transversus abdominis muscle. The kidneys are reddish-brown, bean-shaped organs situated retroperitoneal on the posterior abdominal wall. You can test yourself on the renal arteries with our quiz. Figure 18-27 T2-weighted maximum intensity projection image from a magnetic resonance urogram performed to evaluate urinary obstruction identified in a patient with an obstructing soft tissue mass in the pelvis on unenhanced computed tomography (CT). At one end of each nephron, in the cortex of the kidney, is a cup-shaped structure called the Bowman's capsule. 18-24). Anatomy Where is the renal cortex? The corticomedullary phase is prolonged in the presence of ureteral or venous obstruction and can persist for days in cases of acute tubular necrosis (ATN; Fig. Anatomy of the Kidney and Ureter Parenchyma Cortex Medulla Perirenal fat Capsule Ureter Each kidney has a single renal vein which conducts the blood out of the kidney and is positioned anterior to the artery. Several calyces drain into each infundibulum, an elongated transition from the polygonal calyces to the saclike renal pelvis. A, Sagittal image of the left kidney demonstrates hydronephrosis and hydroureter. All content published on Kenhub is reviewed by medical and anatomy experts. The small portion of the lumen surrounding the papilla is called the calyx. 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. 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). The main function of the kidney is to eliminate excess bodily fluid, salts and byproducts of metabolism this makes kidneys key in the regulation of acid-base balance, blood pressure, and many other homeostatic parameters. While migrating superiorly, the kidneys rotate medially along their long axes and the inferior supplying mesonephric arteries degenerate. Unlike other filling defects within the renal collecting system (e.g., tumor, stone, clot), an aberrant papilla usually has a small fornix around it, seen as a halo on conventional urography (Fig. These surfaces are separated by the edges of the kidney, which are the major convexity laterally, and minor concavity medially. aware of such a vessel, the urologist may choose to perform an alternate procedure to avoid hemorrhagic complications. Horseshoe kidneys result from midline fusion of the kidneys, typically at the level of the origin of the inferior mesenteric artery. The left renal vein passes anteriorly to the aorta just below the trunk of the superior mesenteric artery, which is risky because it can be compressed by one of those two. If a kidney stone becomes lodged in the ureters, it may block the flow of urine and cause the kidney to swell and the ureter to spasm, which can be very painful. Radiologists divide the kidney into three parts: the upper pole, lower pole, and the interpole (which is in between them). 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. Bilateral echogenic kidneys with renal hypertrophy can be seen associated with human immunodeficiency virus disease (see. Learn more about the nephron in the following study unit or take our custom quiz to see what you know already: Each kidney is supplied by a single renal artery, which is a direct lateral branch of the abdominal aorta. urinary system quizzes and labeled diagrams. In this region, the anterior and posterior. All rights reserved. 18-27). The renal cortex and medulla both have high signal intensity on T2-weighted images resulting in poor corticomedullary differentiation. Some divide the excretory phase into the early excretory phase (contrast mainly confined to the kidney) and late excretory phase (contrast in the ureters). A simple calyx receives urine from a single papilla; a compound calyx receives urine from multiple papillae (Fig. In this region, the anterior and posterior hilar lip is identified (Fig. Calcifications and renal calculi are notoriously poorly demonstrated with MRI. Renal function is better evaluated by measured creatinine clearance, which takes into account not only the amount of creatinine in the blood but also the amount of creatinine within a specified volume of urine over a given period. Best, Susan. 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. Luckily, the kidneys also feel this increase of pressure, and in cases when this happens, they increase the filtration rate of blood and production of urine, which subsequently leads to the increase fluid excretion and decrease of blood pressure. For most people, obstruction of a single ureter does not induce renal failure. Hypotension is a stimulus for the kidneys to increase the retention of fluid and thus increase blood pressure. B, The lesion becomes more conspicuous during the nephrographic phase. The medulla consists of multiple pyramidal tissue masses, called the renal pyramids, which are triangle structures that contain a dense network of nephrons. This kidney measured 14 cm in length. The kidneys are paired retroperitoneal structures that are normally located between the transverse processes of T12-L3 vertebrae, with the left kidney typically somewhat more superior in position than the right. In other cases, each renal unit has its own ureter. Illustration demonstrating the relation between the renal papilla and calyx. Volume rendering from a computed tomographic scan of the kidneys shows bilateral supernumerary renal arteries (three on right, two on left). Each time a professor says 'nephron', a student gets a headache. 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. Pearl: Any upward trend in serum creatinine value should be viewed with concern because it implies renal reserve function has already been affected. Renal size can be measured in several ways. Because the interlobular arteries form an arch overlying the pyramid, they are called the arcuate arteries. 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 most superior vessel is the renal vein which exits the kidney, just under it is the renal artery that enters in, and under the artery is the exiting ureter. The hilum of the kidney usually projects at the level of the L2 vertebra. The main symptom is severe sharp pain that starts suddenly, usually in your belly or one side of your back, and it may go away just as quickly. Unenhanced CT can identify hydronephrosis and hydroureter, urinary stones, and some masses. Kidney cysts are round pouches of fluid that form on or in the kidneys. Learning a quickmnemonic'VAD' can help you remember these structures (renal Vein, renal Artery, Duct a.k.a ureter). The parenchyma of the kidney consists of the outer renal cortex, and inner renal medulla. On the other hand, the products of cellular metabolism and drug metabolites are eliminated from the blood which prevents their depositing in the body and potential toxicity. As the lobules of metanephric blastema coalesce to form each kidney, they do not always result in a smooth, uniform band of cortex. The adrenal cortex directly influences renal function through the production of the hormone aldosterone to stimulate sodium reabsorption. The fused kidneys can have a variety of orientations, including side by side, in-line, or perpendicular. The nephrons within the cortex comprise some of the most highly perfused parenchymal tissue in the body. 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. Note distance from origin to the first arterial division (Fig. CT scan and MRI to help diagnose and stage kidney masses. B, Transverse image of the bladder demonstrates a large bladder tumor in the region of the trigone. Figure 18-25 Sagittal ultrasound image of the left kidney demonstrates a unilateral small, smooth, echogenic kidney in a patient with renal artery stenosis. Most serum creatinine is excreted in the urine; therefore, if renal function is compromised, levels of creatinine in the serum increase. The cortex of a normal kidney is usually less echogenic than the adjacent normal liver. 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. 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. Some of them are congenital, such as a third kidney, which is usually atrophic. Table 18-1 Imaging the Living Renal Donor. 18-1). However, T1-weighted images provide good corticomedullary differentiation. Figure 18-22 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. Figure 18-17 Coronal maximum intensity projection image from a contrast-enhanced computed tomographic scan demonstrates a dilated and tortuous lumbar veins joining the left renal vein. Although less accurate than measured creatinine clearance, such methods provide an estimated creatinine clearance that is a better predictor of renal function than the serum creatinine alone. When abnormal echogenicity is detected, it is important to note whether it is unilateral or bilateral. Ultrasound It can be seen as a triangular echogenic cortical defect, frequently seen in upper lobe parenchyma. The phases of nephrogram development and contrast excretion parallel those seen on contrast-enhanced CT with one notable exception (Fig. The anteromedial aspect of the interpolar region is interrupted by the renal hilum to make a C shape. The relation between the UPJ and vascular anatomy can be quite complex. It's not clear what causes simple kidney cysts. Figure 18-5 Illustration demonstrating the anatomy of the renal collecting system. Table 18-6 Causes of Bilateral Small Smooth Kidneys. Typically, one kidney sits on either side of your spine. The kidney is a very important organ in regards to body homeostasis. Renal size and cortical thickness can be assessed in a manner similar to ultrasound. Figure 18-13 Volume rendering from a computed tomographic scan of the kidneys shows bilateral supernumerary renal arteries (three on right, two on left). 18-24). 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. In this way, the consistency of blood is preserved and no important substances are lost. This is just a peek into the kidney physiology. Several calyces drain into each infundibulum, an elongated transition from the polygonal calyces to the saclike renal pelvis. Note that the left renal vein receives blood from the left suprarenal and left testicular veins. Illustration demonstrating the anatomy of the renal collecting system. This illustrates the amount of reserve function that must be compromised before renal injury can be detected with a serum creatinine level. One of the most commonly used (and least complicated) equations is shown in Box 18-1. The renal cortex and medulla both have high signal intensity on T2-weighted images resulting in poor corticomedullary differentiation. Any excessive amount of fluid will increase the pressure on the arterial wall and cause the blood pressure to rise (hypertension). The upper pelvis is the most common ectopic location for the kidney; most cases are also associated with abnormalities of rotation. Note that retroaortic components are usually near the inferior poles (Fig. Note that there is no contrast in the aorta. The patient had acute renal failure; therefore, contrast-enhanced CT was not performed. 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. Kidney cysts can occur with disorders that may impair kidney function. Global insult to one kidney may result in unilateral atrophy that is uniform and smooth. Dialysis. BOX 18-3 Causes of Bilateral Hydronephrosis. Made. 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. 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. Note origin of inferior accessories near inferior poles on each side. More tenuous vascular supply to the renal medulla makes it more susceptible to ischemia. BOX 18-2 Crossing Vessels in Ureteropelvic Junction Obstruction. An acute change in renal cortical echogenicity is occasionally seen with pyelonehritis. Is shown in Box 18-1 to one kidney may result in unilateral atrophy that is uniform and smooth seen... Long axes and the inferior poles ( Fig in a manner similar to ultrasound used and. 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