Frontal image of the left kidney from an intravenous urogram demonstrating an aberrant renal papilla in the lower pole infundibulum. Urine that is concentrated in the renal papilla is subsequently excreted into a lumen lined with transitional epithelium. Due to the segmental vascular supply of the kidney it is often feasible to ligate the relative arteries and veins and remove the tumour with a safe zone of healthy surrounding parenchyma ( partial nephrectomy) without removing the entire kidney or compromising its total vascular supply by ischaemia. 18-9). Simple kidney cysts aren't cancer and rarely cause problems. The isthmus connecting the kidneys is variable, ranging from normal renal cortex to a thin fibrous band. 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. 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. This causes them to fire impulses which stimulate rhythmical contraction and relaxation, called peristalsis. B, Mild hydronephrosis results in rounding of the fornices with mild shortening of the papillary impression. But here is a neat little mnemonic to help. The renal cortex is part of your kidney, which itself is part of the urinary tract. A healthy individual who donates a kidney is likely to maintain a normal serum creatinine despite the loss of 50% of parenchymal tissue. More tenuous vascular supply to the renal medulla makes it more susceptible to ischemia. Static-fluid (T2-weighted) MR urography and phase-contrast MR angiography are useful techniques that do not require intravenous contrast material. Thoracic kidneys are the least common form of renal ectopia. Bone scan and chest x-ray to find out if the cancer has spread. Supernumerary kidneys are quite rare and have been associated with aortic coarctation, vaginal atresia, and urethral duplications. 18-18). 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). Figure 18-2 Annotated axial image of the right kidney from a contrast-enhanced computed tomographic scan demonstrates hilar anatomy of the kidney. 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. Surgery was successful and the surgeon confirmed the anatomic survey was correct. Right-sided pain was related to crossed renal ectopia. Chronic obstruction, however, results in damage to the papilla, evident in the clubbed calyx of papillary necrosis (Fig. 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. Yet, the relations of the kidneys with other organs are often found in Anatomy tests. Most diagnosed kidney growths are small and localized masses. Living renal donor allografts account for more than half of the transplanted kidneys in the United States. Approximately 1 year before presentation, the patient experienced a similar episode of right flank pain that prompted an unenhanced CT examination of the abdomen and pelvis at an outside institution. Depending on where the cyst is located, it can affect how the kidney works. 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. 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 most common cause is renal artery stenosis (see, Delayed but increasingly dense nephrogram, Delayed but hyperconcentrated contrast excretion, Imaging Evaluation of Acute Abdominal Pain, A Multidimensional Approach to Abdominal Imaging. 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. This refers to the forming of the stones within the system of calyces because of too much calcium or uric acid into the filtrate. 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. The small portion of the lumen surrounding the papilla is called the. 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. 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. Figure 18-26 Ultrasound performed for acute renal failure demonstrates bilateral hydronephrosis caused by a bladder tumor. Perhaps of even greater importance, serum creatinine is not a sensitive test for minor insults to the kidney in otherwise healthy individuals. B, The lesion becomes more conspicuous during the nephrographic phase. An acute change in renal cortical echogenicity is occasionally seen with pyelonehritis. If the renal pelvis is entirely within the confines of the renal sinus, it is considered intrarenal. Some of them are congenital, such as a third kidney, which is usually atrophic. Ultrastructurally, the nephron is the functional representative of the kidney. 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. Table 18-6 lists the most common causes of bilateral smooth renal atrophy. Figure 18-16 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 that there is no contrast in the aorta. Obstruction can cause renal failure if it is bilateral (Box 18-3) or if there is preexisting disease in the unobstructed kidney. development and contrast excretion parallel those seen on contrast-enhanced CT with one notable exception (Fig. Learning anatomy is a massive undertaking, and we're here to help you pass with flying colours. Of course, if the situation is the other way around (less than 5 liters of blood), blood pressure is too low (hypotension). 18-2). This layer sits posteriorly and posterolaterally to each kidney and separates it from the muscles of the abdominal wall. On the superior aspect of each kidney is the adrenal gland. Last reviewed: December 28, 2022 These terminal branches have no collateral circulation. Serum creatinine, however, is dependent not only on its disposal but also its production. In other cases, each renal unit has its own ureter. On the other hand, kidneys do have relations with peritoneum, or precisely with the specific organs that are covered with peritoneum which are placed directly adjacent to the kidneys. Typically, one kidney sits on either side of your spine. Size disparity greater than 1.5 cm between kidneys should raise suspicion that one kidney is abnormal. The phases of nephrogram development and contrast excretion parallel those seen on contrast-enhanced CT with one notable exception (Fig. Differential diagnosis General imaging considerations include: renal cortical defect duplex kidney Weve mentioned that the most important functions of the kidney are the regulation of the blood homeostasis and blood pressure, so acute kidney failure can lead to a quick fall of blood pressure which presents as a state of shock. Note distance from origin to the first arterial division (Fig. The right kidney has a normal appearance (not shown). Because they rarely cause symptoms, renal cysts are most often found during . The vessel which brings blood into the glomerulus is the afferent arteriole, whereas the vessel that carries the rest of the blood out that hasnt been filtered out of the glomerulus is called the efferent arteriole. The defect proved to be blood clot from papillary necrosis. On axial sections, the polar regions of the kidney typically form a closed circle or donut shape, with the hole formed by renal sinus fat. 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. Made. In addition to the renal artery, accessory renal arteries are present too. Despite the complexity of renal physiology, many attempt to assess renal function with a simple quantitative measure, the serum creatinine. Ultrasound to get images of your kidneys. The presence of significant renal parenchyma may justify surgical repair to maximize the functional contribution of that kidney. Table 18-1 provides a quick guide itemizing key imaging findings in the potential renal donor. People with unilateral agenesis often are unaware that they lack one kidney until an accidental discovery, since the one kidney that they have is able to functionally compensate for the other. Axial images from contrast-enhanced computed tomography demonstrate transient enhancement of a small renal cell carcinoma. The renal cortex and medulla both have high signal intensity on T2-weighted images resulting in poor corticomedullary differentiation. Now lets pay attention to the borders of the kidneys. In other cases, each renal unit has its own ureter. Note that retroaortic components are usually near the inferior poles (Fig. Figure 18-11 Three-dimensional volume rendering from contrast-enhanced multidetector computed tomography examination of the kidneys demonstrates typical orientation of a horseshoe kidney. 18-24). Renal size and cortical thickness can be assessed in a manner similar to ultrasound. A, Tips of the fornices are sharply defined. The left kidney appeared unremarkable. The presence of contour irregularity usually indicates scarring, suggesting prior infection, reflux, or infarction. 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. The kidneys help remove waste products from the . BOX 18-2 Crossing Vessels in Ureteropelvic Junction Obstruction. However, small, low-attenuation lesions in the medulla are often obscured during this phase. As the lobules of metanephric blastema coalesce to form each kidney, they do not always result in a smooth, uniform band of cortex. 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. Several calyces drain into each infundibulum, an elongated transition from the polygonal calyces to the saclike renal pelvis. Note origin of inferior accessories near inferior poles on each side. Because an extrarenal pelvis is not confined by the renal parenchyma, there is a tendency for it to expand. Calcifications and renal calculi are notoriously poorly demonstrated with MRI. The early excretory phase begins as early as 120 seconds after injection. Advantages of scintigraphy include accurate quantitative measurement of function. Also, in situations with notable blood losses, kidneys release a hormone called erythropoietin, which stimulates bone marrow to produce more blood cells. This method is the standard in evaluation of UPJ obstruction and often is used for other types of chronic obstruction. Sometimes, one or both kidneys fail to develop, which causes unilateral or bilateral renal agenesis. Unilateral renal agenesis occurs in approximately 1 in 1000 individuals with minimal impact on health, although it is sometimes associated with other congenital anomalies of the genitourinary tract and musculoskeletal system. Fever. So the pyramids represent the functional tissue that creates urine, whereas the calyces are the beginning of the ureter and transport the urine to it. For most people, obstruction of a single ureter does not induce renal failure. Poorly functioning kidneys with little residual parenchymal volume may be removed because preservation offers opportunities for future complications (infection, hypertension) without contributing significantly to renal function. 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. Made aware of such a vessel, the urologist may choose to perform an alternate procedure to avoid hemorrhagic complications. Reading time: 23 minutes. A frontal section through the kidney reveals an outer region called the renal cortex and an inner region called the renal medulla (Figure 25.1.2). While migrating superiorly, the kidneys rotate medially along their long axes and the inferior supplying mesonephric arteries degenerate. In this case, the right kidney had more favorable anatomy for laparoscopic donor nephrectomy. Several formulas are available for this calculation, and calculators and on-line sites are available to simplify the calculations. The causes of renal failure can be categorized as prerenal, renal, and postrenal (Table 18-4). 18-3). Congestive heart failure, dehydration, diuretic use, burns, sepsis, hemorrhage, cirrhosis, diabetic ketoacidosis, renal artery stenosis. 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