Perhaps of even greater importance, serum creatinine is not a sensitive test for minor insults to the kidney in otherwise healthy individuals. Global insult to one kidney may result in unilateral atrophy that is uniform and smooth. 18-13). The uniform high attenuation of the nephrographic phase provides an optimal background for detecting small, low-attenuation lesions in the renal parenchyma (Fig. Ultrasound It can be seen as a triangular echogenic cortical defect, frequently seen in upper lobe parenchyma. Thus, any upward trend in the serum creatinine value should be viewed with concern when considering the administration of potentially nephrotoxic or renally excreted intravenous contrast media. The patient had right flank pain but had a solitary calcification in the left pelvis on plain radiograph (not shown). 18-10). Note number of veins by inspecting inferior vena cava along entire length of kidney. Internal Anatomy. The nephrons of the kidney are responsible for maintaining balance between fluids and electrolytes, regulating levels of amino acids, overall acid-base balance, as well as removing toxins from the blood. The small portion of the lumen surrounding the papilla is called the calyx. These are chronic processes that lead to a loss of renal cortex gradually and uniformly. The medial border of the kidney contains a very important landmark called the hilum of the kidney, which is the entry and exit point for the kidney vessels and ureter. In some cases, two separate kidneys drain into a bifid renal pelvis, ultimately drained by a common ureter. 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 pyramids are separated by extensions of the cortex called the renal columns. Urine that is concentrated in the renal papilla is subsequently excreted into a lumen lined with transitional epithelium. A, Axial image demonstrates the dilated renal pelvis and crossing vessel. The small portion of the lumen surrounding the papilla is called the. Diabetes, hypertension, acute tubular necrosis, Increased echogenicity has high association with parenchymal disease, Acute tubular necrosis usually results in an increased RI, whereas prerenal causes usually do not have an increased RI; postrenal causes often increase the RI, but hydronephrosis should be present in those cases, If present, suspect neurogenic bladder or outlet obstruction, Often severe aortic disease or fibromuscular dysplasia. They are branches of the abdominal aorta and all together are called the extrahilar renal arteries. A second similar finely granular mass was present in the interpolar region, and it also contained . BOX 18-2 Crossing Vessels in Ureteropelvic Junction Obstruction. Kenhub. Created for people with ongoing healthcare needs but benefits everyone. At one end of each nephron, in the cortex of the kidney, is a cup-shaped structure called the Bowman's capsule. For that reason, we got you covered with this topic nicely and concisely. Supernumerary kidneys are quite rare and have been associated with aortic coarctation, vaginal atresia, and urethral duplications. 18-16). Figure 18-25 Sagittal ultrasound image of the left kidney demonstrates a unilateral small, smooth, echogenic kidney in a patient with renal artery stenosis. Blood in the urine, or dark urine. Figure 18-8 Junctional cortical line seen on a long-axis ultrasound image of the right kidney. Figure 18-10 Crossed ectopia on intravenous pyelogram. However, this individual is more likely to show a decline in renal function from an additional insult. Kim Bengochea, Regis University, Denver. Look for duplication, large extrarenal pelvis. The medulla is the inner region of the parenchyma of the kidney. A bean-like structure like the kidney has two borders: medial and lateral. The large left proximal ureteral stone seen in this image is only partially obstructing, causing mild dilation in the left kidney collecting system. 2023 Differential diagnosis General imaging considerations include: renal cortical defect duplex kidney 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. The defect proved to be blood clot from papillary necrosis. Table 18-5 summarizes a checklist approach to the ultrasound examination. Chronic obstruction, however, results in damage to the papilla, evident in the clubbed calyx of papillary necrosis (Fig. 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. For most people, obstruction of a single ureter does not induce renal failure. 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. Copyright The interpolar region is the middle of the kidney. normal kidney size in adults normal kidney size in children Structure Pearl: Any upward trend in serum creatinine value should be viewed with concern because it implies renal reserve function has already been affected. This layer sits posteriorly and posterolaterally to each kidney and separates it from the muscles of the abdominal wall. It doesn't have to be that way. Figure 18-13 Volume rendering from a computed tomographic scan of the kidneys shows bilateral supernumerary renal arteries (three on right, two on left). This is called the nutcracker phenomenon. Ultrasound permits real-time optimization of imaging relative to the axis of each kidney. They are staged the same way as the renal pelvis. 18-23). Ultrasound performed for acute renal failure demonstrates bilateral hydronephrosis caused by a bladder tumor. Chronic glomerulonephritis usually causes bilateral increased renal echogenicity with smooth atrophy, whereas renal artery stenosis usually causes a similar but unilateral appearance (Fig. Note origin of inferior accessories near inferior poles on each side. Anatomy of the Kidney and Ureter Parenchyma Cortex Medulla Perirenal fat Capsule Ureter The left kidney (not shown) had a similar appearance. Note that the left renal vein receives blood from the left suprarenal and left testicular veins. Last reviewed: December 28, 2022 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. Imaging must provide detailed images of the renal parenchyma and a survey of arterial, venous, and ureteral anatomy. Each pyramid creates urine and terminates into a renal papilla. After looking at the overview of the kidneys in situ, it may seemas they are cluttered with all abdominal organs. 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. In other cases, each renal unit has its own ureter. The right kidney has a normal appearance (not shown). 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. Also, in situations with notable blood losses, kidneys release a hormone called erythropoietin, which stimulates bone marrow to produce more blood cells. However, you may have symptoms related to the condition that's causing it. Pain that radiates to the lower abdomen and groin. Aggressive tumors form, grow and spread very quickly. Box 18-2 provides some tips regarding crossing vessels in UPJ obstruction. Table 18-5 Checklist Approach to Ultrasound for Renal Failure. Prominent extrarenal pelves are typically positioned anteriorly (Fig. The parenchyma of the kidney consists of the outer renal cortex, and inner renal medulla. AMLs can bleed and while not cancerous are still taken very seriously. These terminal branches have no collateral circulation. 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. These surfaces are separated by the edges of the kidney, which are the major convexity laterally, and minor concavity medially. 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. Figure 18-26 Ultrasound performed for acute renal failure demonstrates bilateral hydronephrosis caused by a bladder tumor. I would honestly say that Kenhub cut my study time in half. 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. Localized means that the tumor has not spread out from where it first started. 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. The calcium or uric acid will precipitate and form stones. This apical projection is called the renal papilla and it opens to the minor calyx. The phases of nephrogram. Note that retroaortic components are usually near the inferior poles (Fig. General symptoms of kidney problems include: blood in your urine . Arterial stenosis was confirmed by magnetic resonance angiography. 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. This kidney measured 14 cm in length. If the renal pelvis extends out of the renal sinus, it is considered to be an extrarenal pelvis (Fig. 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. 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. In the medulla, 5-8 renal pyramids are separated by connective tissue renal columns. Since they are located deep retroperitoneally, the easiest way to examine them is from the patients back. The visible contrast seen in the excretory phase has been concentrated many-fold. Anatomy Where is the renal cortex? Usually, there are two to three major calyces in the kidney (superior, middle, and inferior), which again unite to form the renal pelvis from which the ureter emerges and leaves the kidney through the hilum. 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. Differential diagnosis General imaging considerations include: renal cortical defect duplex kidney 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. aware of such a vessel, the urologist may choose to perform an alternate procedure to avoid hemorrhagic complications. The anteromedial aspect of the interpolar region is interrupted by the renal hilum to make a C shape. Comparative views of the CT scan ( a axial, b coronal, and c sagittal planes) and corresponding views of the physical model ( d superior view, e median view, and f median view). 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 the complexity of renal physiology, many attempt to assess renal function with a simple quantitative measure, the serum creatinine. 18-15). Figure 18-1 Annotated three-dimensional volume rendering of the left kidney acquired using a combined nephrographic phase and excretory phase during computed tomographic urography demonstrates regional anatomy of the kidney. In this case, the right kidney had more favorable anatomy for laparoscopic donor nephrectomy. The patient had right flank pain but had a solitary calcification in the left pelvis on plain radiograph (not shown). Each kidney has a single renal vein which conducts the blood out of the kidney and is positioned anterior to the artery. more lateral and anterior than the superior poles. 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. There is no specific treatment for fused kidneys and the only option is to treat the pathologies that affect them during life. Recent advances in MDCT and MRI permit cross-sectional vascular studies to replace conventional angiography before UPJ repair (Fig. This illustrates the amount of reserve function that must be compromised before renal injury can be detected with a serum creatinine level. Table 18-7 lists causes of unilateral smooth renal atrophy. 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. BOX 18-3 Causes of Bilateral Hydronephrosis. This specific condition is called the nutcracker phenomenon. Horseshoe kidneys result from midline fusion of the kidneys, typically at the level of the origin of the inferior mesenteric artery. Renal cysts become fairly common as people age and usually do not cause symptoms or harm. Ultrasound It can be seen as a triangular echogenic cortical defect, frequently seen in upper lobe parenchyma. Reading time: 23 minutes. The portion of the kidney between the poles is called the interpolar region and contains the renal hilum (Fig. Chronic glomerulonephritis usually causes bilateral increased renal echogenicity with smooth atrophy, whereas renal artery stenosis usually causes a similar but unilateral appearance (Fig. 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. On the other hand, babies with bilateral agenesis cannot survive without an immediate kidney transplant. Entities for which sonography is most useful. Let's see what is nephron and how it is structured,so you can remember it for good. There are many clinical states related to kidney malfunction. The left kidney appeared unremarkable. A, Soft-tissue windows demonstrate no filling defect. The information we provide is grounded on academic literature and peer-reviewed research. The main unit of the medulla is the renal pyramid. 18-1). A, A low-attenuation lesion is difficult to identify during the corticomedullary phase. The fused kidneys can have a variety of orientations, including side by side, in-line, or perpendicular. When simple kidney cysts do cause symptoms, they might include: Pain in the side between the ribs and hip, stomach or back. As the lobules of metanephric blastema coalesce to form each kidney, they do not always result in a smooth, uniform band of cortex. 18-20). Dialysis. You can test yourself on the renal arteries with our quiz. 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. Jana Vaskovi MD This can cause varicocele of the left testicle because gravity works against the column of the blood in the left testicular vein. 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). Read more. When fused, the condition is described as crossed fused ectopia. 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. Obstruction can cause renal failure if it is bilateral (Box 18-3) or if there is preexisting disease in the unobstructed kidney. Living renal donor allografts account for more than half of the transplanted kidneys in the United States. Several formulas are available for this calculation, and calculators and on-line sites are available to simplify the calculations. 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. Learning a quickmnemonic'VAD' can help you remember these structures (renal Vein, renal Artery, Duct a.k.a ureter). Unenhanced MRI can also be used to diagnose obstruction and identify the source (Fig. Increased cortical echogenicity is associated with many forms of chronic renal parenchymal disease and indicates a renal cause for renal failure. Axial images from contrast-enhanced computed tomography demonstrate transient enhancement of a small renal cell carcinoma. 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 normal appearance of the calyx is created by the impression of the renal papilla. 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