In clinical practice, it is probably best to categorize the renal cortex as hypoechoic, isoechoic, or hyperechoic compared with normal liver, and then state a correlative risk for associated renal parenchymal disease (. Bone scan and chest x-ray to find out if the cancer has spread. Both renal arteries, left and right, arise just below the superior mesenteric artery, with the left renal artery positioned slightly superiorly to the right one. The genital system consists of the testes, epididymides, deferent ducts, seminal vesicles, ejaculatory ducts, the prostate, and the penis in males; and the ovaries, uterine tubes, uterus, and vagina in females. 18-6). 18-23). Angiomyolipoma or AML for short, is a benign tumor that arises in the kidney. General symptoms of kidney problems include: blood in your urine . 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. Obstruction can cause renal failure if it is bilateral (Box 18-3) or if there is preexisting disease in the unobstructed kidney. Blood in the urine, or dark urine. Internal Anatomy. A, Enhancement of the mass is conspicuous in the corticomedullary phase. The glomerulus is actually a web of arterioles and capillaries, with a special filter which filters the blood that runs through the capillaries, the glomerular membrane. Coronal maximum intensity projection image from a contrast-enhanced computed tomographic scan demonstrates a dilated and tortuous lumbar veins joining the left renal vein. Size and Contour of Diffuse Renal Disease, 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, Global insult to one kidney may result in unilateral atrophy that is uniform and smooth. However, small, low-attenuation lesions in the medulla are often obscured during this phase. Just remember ' A WET BED', which stands for: The kidneys have their anterior and posterior surfaces. February 12, 2018 - 2:17pm BOX 18-3 Causes of Bilateral Hydronephrosis. 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. The upper poles are normally oriented more medially and posteriorly than the lower poles. BOX 18-1 Cockroft and Gault Equation for Calculating Estimated Creatinine Clearance. 18-10). 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. Reading time: 23 minutes. Horseshoe kidneys result from midline fusion of the kidneys, typically at the level of the origin of the inferior mesenteric artery. CT scan and MRI to help diagnose and stage kidney masses. However, this individual is more likely to show a decline in renal function from an additional insult. It doesn't have to be that way. 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. impression is preserved. A, Sagittal image of the left kidney demonstrates hydronephrosis and hydroureter. 3D printed model for a 53-year-old female presenting a 21 15 15 mm renal tumor located in the interpolar region of left kidney, treated by left partial nephrectomy. . 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. Because the fascia of the retroperitoneum prevents significant extravasation, the incision usually heals to form a larger lumen. 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. If this appearance were present bilaterally, chronic renal disease such as chronic glomerulonephritis would be a more likely explanation. 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. However, T1-weighted images provide good corticomedullary differentiation. Estimated creatinine clearance may be calculated using serum creatinine with adjustments made for sex, age, and body weight. After looking at the overview of the kidneys in situ, it may seemas they are cluttered with all abdominal organs. Use of MR contrast agents in renal failure poses a lower risk than iodinated contrast material for exacerbating renal failure, but there is evidence that gadolinium-based MR contrast media pose some risk for systemic complications (nephrogenic systemic fibrosis) and should be used with caution in patients with severe or acute renal insufficiency. Three-dimensional volume rendering from contrast-enhanced multidetector computed tomography examination of the kidneys demonstrates typical orientation of a horseshoe kidney. The shape of the calyx is formed by the impression of the renal papilla. Finally, the arcuate arteries branch into the interlobular arteries which branch off even further by giving afferent arterioles to run blood past the glomerulus for blood filtration. 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. The cortex of a normal kidney is usually less echogenic than the adjacent normal liver. Renal scintigraphy can be performed with a variety of agents to provide assessment of either function or structure of the kidneys. 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. Despite the complexity of renal physiology, many attempt to assess renal function with a simple quantitative measure, the serum creatinine. Cells in our body constantly produce hydrogen ions. At the Brady Urological Institute, we believe in the adage, "An ounce of prevention is worth a pound of cure," so we place great emphasis on a thorough metabolic evaluation, so that therapies can be appropriately directed towards reducing the risk of recurrent stone disease. 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. 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). Yet, the relations of the kidneys with other organs are often found in Anatomy tests. The kidneys help remove waste products from the . Annotated axial image of the right kidney from a contrast-enhanced computed tomographic scan demonstrates hilar anatomy of the kidney. 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. A second similar finely granular mass was present in the interpolar region, and it also contained . Imaging must provide detailed images of the renal parenchyma and a survey of arterial, venous, and ureteral anatomy. 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. The medulla consists of multiple pyramidal tissue masses, called the renal pyramids, which are triangle structures that contain a dense network of nephrons. 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. This significantly affects the testicle, since an obstruction of drainage causes an obstruction of fresh arterial blood inflow, which can result in the infarction of testicular tissue. 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. 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. Note origin of inferior accessories near inferior poles on each side. 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 superior poles (extremities) (T12) of both kidneys are more medially pointed towards the spine than the inferior poles (extremities) (L3). The axes of the renal moeities are abnormal with the inferior poles angled medially. 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. 18-25). 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. Kim Bengochea, Regis University, Denver. The center of the minor concavity is marked as the hilum of the kidney where the renal artery enters the kidney, and the renal vein and ureter leave the kidney. B, Low-attenuation lesion in the late nephrographic/early excretory phase is less suspicious in appearance. The renal cortex and medulla both have high signal intensity on T2-weighted images resulting in poor corticomedullary differentiation. Maintaining kidney health. There is no specific treatment for fused kidneys and the only option is to treat the pathologies that affect them during life. It is also permeable for the products of the metabolism, such are creatinine and drug metabolites. Jana Vaskovi MD Supernumerary kidneys are quite rare and have been associated with aortic coarctation, vaginal atresia, and urethral duplications. CT angiography is occasionally performed when a vascular causative factor is suspected (renal artery stenosis or renal vein thrombosis) and MRI is contraindicated. print Print this Article 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. They are branches of the abdominal aorta and all together are called the extrahilar renal arteries. This phenomenon is due to T2-shortening and susceptibility (T2*) effects caused by concentrated gadolinium, and can potentially obscure filling defects and urothelial lesions. A potential benefit of MRI is the lack of exposure to ionizing radiation, although unenhanced CT would still be required to detect stones (the presence of stones increases the donors risk for renal insufficiency later in life and could disqualify them as a donor candidate). The ureter and calyces were not dilated (not shown), helping to differentiate this anatomic variant from obstruction. It's not clear what causes simple kidney cysts. Illustration demonstrating the anatomy of the renal collecting system. The initiation is caused by the increase in volume that stretches the walls of the calyces. An acute change in renal cortical echogenicity is occasionally seen with pyelonehritis. 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). 18-25). 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). It is notable that the kidney has a very rich blood supply. When hydronephrosis is absent, the causative factor for acute renal failure is almost certainly prerenal or renal. 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. A, Soft-tissue windows demonstrate no filling defect. The solid renal parenchyma consists of the peripheral renal cortex and more central renal medulla. more lateral and anterior than the superior poles. It is important to note, however, that the appearance of hydronephrosis does not necessarily indicate urinary obstruction (see Hydronephrosis and Its Mimics section later in this chapter). The stones can move into the ureter and literally get stuck there because the lumen of the ureter is much smaller compared to the calyces, which is very painful for the patient. 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. Made aware of such a vessel, the urologist may choose to perform an alternate procedure to avoid hemorrhagic complications. Figure 18-6 Frontal image of the left kidney from an intravenous urogram demonstrating an aberrant renal papilla in the lower pole infundibulum. Figure 18-7 Axial image of the left kidney from a contrast-enhanced computed tomographic scan demonstrates an extrarenal pelvis. Register now Ultrasound is usually used in the initial evaluation of the patient with newly diagnosed renal failure. Always include unenhanced computed tomographic images to look for renal stones. The dynamics of obstruction and quantification of relative renal function between the two kidneys may be important considerations in two general circumstances: (1) it is unclear whether obstruction is severe enough to warrant surgical intervention; or (2) significant parenchymal atrophy exists, and the relative merits of repair and nephrectomy are being compared. C, More severe hydronephrosis results in more pronounced shortening of the papilla. The solid renal parenchyma consists of the peripheral renal cortex and more central renal medulla. In clinical practice, it is probably best to categorize the renal cortex as hypoechoic, isoechoic, or hyperechoic compared with normal liver, and then state a correlative risk for associated renal parenchymal disease (Table 18-2). On ultrasound, the renal cortex is usually echogenic in this setting. The patient had acute renal failure; therefore, contrast-enhanced CT was not performed. The visible contrast seen in the excretory phase has been concentrated many-fold. A simple calyx receives urine from a single papilla; a compound calyx receives urine from multiple papillae (Fig. The anterior surface faces towards the anterior abdominal wall, whereas the posterior surface is facing the posterior abdominal wall. The interpolar region is the middle of the kidney. In the medulla, 5-8 renal pyramids are separated by connective tissue renal columns. In general, the amount of blood in the body is 5 liters. IVC, Inferior vena cava. 18-27). The calyces, however, will have a normal appearance with an unobstructed extrarenal pelvis but will be dilated in cases of urinary obstruction. Perhaps of even greater importance, serum creatinine is not a sensitive test for minor insults to the kidney in otherwise healthy individuals. The kidneys serve important . Each end of the kidney is commonly called a pole. chronic obstruction, or severe or repeated urinary infections. Depending on where the cyst is located, it can affect how the kidney works. All content published on Kenhub is reviewed by medical and anatomy experts. These terminal branches have no collateral circulation. This specific condition is called the nutcracker phenomenon. Of course, if the situation is the other way around (less than 5 liters of blood), blood pressure is too low (hypotension). When echogenicity of the renal cortex equals that of the liver, renal function is abnormal in approximately 38% of cases. But more often, kidney cysts are a type called simple kidney cysts. 18-24). The relation between the UPJ and vascular anatomy can be quite complex. Sagittal ultrasound image of the right kidney demonstrates increased size and echogenicity of the kidney, findings typical of human immunodeficiency virus nephropathy. Identify abnormal course of main or accessory right renal artery anterior rather than posterior to inferior vena cava (Fig. If the renal pelvis is entirely within the confines of the renal sinus, it is considered intrarenal. The large left proximal ureteral stone seen in this image is only partially obstructing, causing mild dilation in the left kidney collecting system. Reviewer: 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. Thoracic kidneys are the least common form of renal ectopia. urinary system quizzes and labeled diagrams. Localized means that the tumor has not spread out from where it first started. Made. In this case, the right kidney had more favorable anatomy for laparoscopic donor nephrectomy. Renal size can be measured in several ways. BOX 18-2 Crossing Vessels in Ureteropelvic Junction Obstruction. Chronic obstruction, however, results in damage to the papilla, evident in the clubbed calyx of papillary necrosis (Fig. 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. A, Axial image from contrast-enhanced computed tomography (CT) demonstrates an accessory right renal artery coursing anterior to the IVC. Calculation of the estimated renal volume is considered by some to be the most accurate assessment of renal size available with ultrasound, although renal length alone is more commonly reported. The nephrons within the cortex comprise some of the most highly perfused parenchymal tissue in the body. Hypotension is a stimulus for the kidneys to increase the retention of fluid and thus increase blood pressure. This causes them to fire impulses which stimulate rhythmical contraction and relaxation, called peristalsis. In most cases, the kidneys are situated with the inferior poles slightly more lateral and anterior than the superior poles. Ultrasound to get images of your kidneys. If the renal pelvis extends out of the renal sinus, it is considered to be an. Ultrasound permits real-time optimization of imaging relative to the axis of each kidney. The left kidney measured 7.8 cm, and the right kidney measured 10.9 cm. If the renal pelvis extends out of the renal sinus, it is considered to be an extrarenal pelvis (Fig. Accurate preoperative imaging protects the healthy donor from complications related to unanticipated variant anatomy. The patient had right flank pain but had a solitary calcification in the left pelvis on plain radiograph (not shown). Occasionally, a papilla will communicate directly with an infundibulum or the renal pelvis and is considered to be an aberrant papilla. 18-8). Bilateral echogenic kidneys with renal hypertrophy can be seen associated with human immunodeficiency virus disease (see Fig. A, Axial image demonstrates the dilated renal pelvis and crossing vessel. Since they are located deep retroperitoneally, the easiest way to examine them is from the patients back. The opposite situation is possible too, if the kidneys excrete too many hydrogen ions, the pH of blood becomes too alkaline, and leads to a state called alkalosis. Fever. The left testicular vein must ascend higher and it drains to the left renal vein at a right angle, unlike the right testicular vein which joins the inferior vena cava directly. 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. Differential diagnosis General imaging considerations include: renal cortical defect duplex kidney The medulla is the inner region of the parenchyma of the kidney. An increased amount of hydrogen ions can acidify the blood and cause a state called acidosis. When simple kidney cysts do cause symptoms, they might include: Pain in the side between the ribs and hip, stomach or back. "Angio" indicates blood vessels, "myo" indicates muscle, and "lipoma" indicates fat. The pyramids contain the functional units of the kidney, the nephrons, which filter blood in order to produce urine which then is transported through a system of the structures called calyces which then transport the urine to the ureter. The isthmus connecting the kidneys is variable, ranging from normal renal cortex to a thin fibrous band. Extraaortic origin of the renal arteries and accessory renal arteries are common. The right kidney has a normal appearance (not shown). For most people, obstruction of a single ureter does not induce renal failure. Kidney cysts are round pouches of fluid that form on or in the kidneys. Figure 18-21 Axial images from contrast-enhanced computed tomography demonstrate transient enhancement of a small renal cell carcinoma. Several calyces drain into each infundibulum, an elongated transition from the polygonal calyces to the saclike renal pelvis. This is because the liver and the stomach offset the symmetry of the abdomen, with the liver forcing the right kidney a bit down, and the stomach forcing the left kidney a bit up. Other methods include classical surgical removal of the stone, either through the ureter or by open surgery. 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. MR angiography can be useful for the diagnosis of renal vascular abnormalities. 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