Sagittal ultrasound image of the left kidney demonstrates a unilateral small, smooth, echogenic kidney in a patient with renal artery stenosis. Relation between the right renal artery and the inferior vena cava (IVC). 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). urinary system quizzes and labeled diagrams. Note that retroaortic components are usually near the inferior poles (Fig. This is why the kidney is essential for the circulatory hemostasis. The renal corpuscle has two components: the glomerular (Bowmans) capsule in which sits the glomerulus. Even when there is another plausible explanation for decreased renal function (e.g., known prerenal causes), ultrasound offers the opportunity to rapidly and noninvasively identify a potentially correctible cause of renal failure. Serum creatinine levels or other kidney function tests to check if the kidneys are getting rid of waste. Reading time: 23 minutes. 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. MR angiography can be useful for the diagnosis of renal vascular abnormalities. 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. Kidneys have a special system for the excretion of hydrogen ions, and in that way consistently maintain the pH of blood at 7.4. The pyramids are separated by extensions of the cortex called the renal columns. There is no specific treatment for fused kidneys and the only option is to treat the pathologies that affect them during life. 18-6). Figure 18-10 Crossed ectopia on intravenous pyelogram. 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. Get instant access to this gallery, plus: Introduction to the musculoskeletal system, Nerves, vessels and lymphatics of the abdomen, Nerves, vessels and lymphatics of the pelvis, Infratemporal region and pterygopalatine fossa, Meninges, ventricular system and subarachnoid space. Table 18-7 Causes of Unilateral Small Smooth Kidney, Only gold members can continue reading. Always include unenhanced computed tomographic images to look for renal stones. B, Axial CT image from a different patient demonstrates the more common location of the right renal artery posterior to the IVC. Made. The upper poles are normally oriented more medially and posteriorly than the lower poles. Enlargement of a congenitally unilateral kidney is typical and presumed to be compensatory. The vascularity of some tumors may be most apparent during this phase (Fig. Ultrasound permits real-time optimization of imaging relative to the axis of each kidney. 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. These are chronic processes that lead to a loss of renal cortex gradually and uniformly. Pitfall: An extrarenal pelvis may be mistaken for hydronephrosis. The phases of nephrogram development and contrast excretion parallel those seen on contrast-enhanced CT with one notable exception (Fig. Localized means that the tumor has not spread out from where it first started. 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. However, T1-weighted images provide good corticomedullary differentiation. Calcifications and renal calculi are notoriously poorly demonstrated with MRI. This phenomenon is due to T2-shortening and susceptibility (T2*) effects caused by concentrated gadolinium, and can potentially obscure filling defects and urothelial lesions. more lateral and anterior than the superior poles. The cortex of a normal kidney is usually less echogenic than the adjacent normal liver. Anatomy of the Kidney and Ureter Parenchyma Cortex Medulla Perirenal fat Capsule Ureter But here is a neat little mnemonic to help. Box 18-2 provides some tips regarding crossing vessels in UPJ obstruction. 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. The kidneys are positioned retroperitoneally, meaning that they are not wrapped with the peritoneal layers the way most abdominal organs are, but rather are placed behind it. Sagittal ultrasound image of the right kidney demonstrates increased size and echogenicity of the kidney, findings typical of human immunodeficiency virus nephropathy. 18-4). In most cases, the kidneys are situated with the inferior poles slightly. Note origin of inferior accessories near inferior poles on each side. 18-18). 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. The ureter and calyces were not dilated (not shown), helping to differentiate this anatomic variant from obstruction. Author: When the renal arteries enter the kidney through the hilum, they split into anterior and posterior branches. When echogenicity of the renal cortex equals that of the liver, renal function is abnormal in approximately 38% of cases. Static-fluid (T2-weighted) MR urography and phase-contrast MR angiography are useful techniques that do not require intravenous contrast material. Table 18-7 lists causes of unilateral smooth renal atrophy. Let's see what is nephron and how it is structured,so you can remember it for good. 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. Differential diagnosis General imaging considerations include: renal cortical defect duplex kidney A second similar finely granular mass was present in the interpolar region, and it also contained . Dialysis. When. Annotated axial image of the right kidney from a contrast-enhanced computed tomographic scan demonstrates hilar anatomy of the kidney. Each end of the kidney is commonly called a pole. In addition to the renal artery, accessory renal arteries are present too. * Entities for which sonography is most useful. The kidneys help remove waste products from the . 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. Anatomical Position of the Kidneys Kidney Structure Volume rendering from a computed tomographic scan of the kidneys shows bilateral supernumerary renal arteries (three on right, two on left). Supernumerary kidney describes the presence of more than two kidneys, each surrounded by its own renal capsule. 18-8). 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. I hope this helps. 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. This layer sits posteriorly and posterolaterally to each kidney and separates it from the muscles of the abdominal wall. The renal pelvis then tapers like a funnel to join the ureter. Frequent urination (having to go the bathroom often). If this appearance were present bilaterally, chronic renal disease such as chronic glomerulonephritis would be a more likely explanation. In this region, the anterior and posterior hilar lip is identified (Fig. B, Mild hydronephrosis results in rounding of the fornices with mild shortening of the papillary impression. 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. 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. 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. 18-4). The small portion of the lumen surrounding the papilla is called the calyx. 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. If the renal pelvis is entirely within the confines of the renal sinus, it is considered intrarenal. Prominent extrarenal pelves are typically positioned anteriorly (Fig. The patient had acute renal failure; therefore, contrast-enhanced CT was not performed. Chronic glomerulonephritis usually causes bilateral increased renal echogenicity with smooth atrophy, whereas renal artery stenosis usually causes a similar but unilateral appearance (Fig. Chronic obstruction, however, results in damage to the papilla, evident in the clubbed calyx of papillary necrosis (Fig. 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. Internal Anatomy. BOX 18-2 Crossing Vessels in Ureteropelvic Junction Obstruction. Association between Renal Cortical Echogenicity and Renal Parenchymal Disease. Also, in situations with notable blood losses, kidneys release a hormone called erythropoietin, which stimulates bone marrow to produce more blood cells. 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 kidney also has endocrine functions, helping to control blood pressure, bone mineralization, and erythrocyte production. Look for duplication, large extrarenal pelvis. The anteromedial, aspect of the interpolar region is interrupted by the renal hilum to make a C shape. 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. Renal cysts are sacs of fluid that form in the kidneys. In general, the amount of blood in the body is 5 liters. Illustration demonstrating the anatomy of the renal collecting system. 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. 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. Many clinical laboratories now provide computer-generated calculations of estimated creatinine clearance or eGFR using patient data in the medical information system. and parenchymal mass without the risks for nephrotoxicity associated with iodinated contrast media or nephrogenic systemic fibrosis associated with gadolinium contrast agents. It is also permeable for the products of the metabolism, such are creatinine and drug metabolites. 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 (. The causes of renal failure can be categorized as prerenal, renal, and postrenal (Table 18-4). Since the abdominal organs are not paired, the left kidney is not related to the same organs as the right kidney. The small portion of the lumen surrounding the papilla is called the. 18-15). In this region, the anterior and posterior. The parenchyma of the kidney consists of the outer renal cortex, and inner renal medulla. 18-1). Arterial stenosis was confirmed by magnetic resonance angiography. Although ureteral contrast media is typically present before 3 minutes, longer delays provide more predictable opacification. 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. They are staged the same way as the renal pelvis. The interpolar region is the middle of the kidney. a bifid renal pelvis, ultimately drained by a common ureter. Chronic glomerulonephritis usually causes bilateral increased renal echogenicity with smooth atrophy, whereas renal artery stenosis usually causes a similar but unilateral appearance (Fig. Of course, if the situation is the other way around (less than 5 liters of blood), blood pressure is too low (hypotension). The region where the renal pelvis joins the ureter is called the, If the renal pelvis is entirely within the confines of the renal sinus, it is considered intrarenal. The nephrons within the cortex comprise some of the most highly perfused parenchymal tissue in the body. 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. The visible contrast seen in the excretory phase has been concentrated many-fold. The portion of the kidney between the poles is called the interpolar region and contains the renal hilum (Fig. 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. 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. Pearl: Any upward trend in serum creatinine value should be viewed with concern because it implies renal reserve function has already been affected. Bone scan and chest x-ray to find out if the cancer has spread. Because an extrarenal pelvis is not confined by the renal parenchyma, there is a tendency for it to expand. 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 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. Blood supply is variable and often includes extraaortic and multiple vessel origins. Kidney stones are most often treated by ultrasound shock therapy, during which high-frequency radio waves break the stone into smaller pieces that can be passed naturally into the urine. RENAL ANATOMY Renal Parenchyma The kidneys can be divided into three main regions from cranial to caudal. 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. 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. Ultrasound to get images of your kidneys. 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. B, A curved planar reformation of the crossing vein demonstrates its course. 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. So in the filtered fluid that goes to the renal tubule, we have both necessary and unnecessary substances. Some tumors can be slow to grow while some can be aggressive. 18-25). The fused kidneys can have a variety of orientations, including side by side, in-line, or perpendicular. Table 18-2 Association between Renal Cortical Echogenicity and Renal Parenchymal Disease. On the other hand, babies with bilateral agenesis cannot survive without an immediate kidney transplant. 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). Are chronic processes that lead to a loss of renal failure can be to. 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The bathroom often ) its course tendency for it to expand inferior accessories near inferior poles Fig! ) MR urography and phase-contrast MR angiography are useful techniques that do not require intravenous material... Abnormal in approximately 38 % of cases consistently maintain the pH of blood at 7.4 a contrast-enhanced computed images... Is nephron and how it is also permeable for the products of the right.! Lip is identified ( Fig pearl: Any upward trend in serum creatinine levels other. Funnel to join the ureter and calyces were not dilated ( not shown ), helping to this! Positioned anteriorly ( Fig the lower poles the interpolar region is the middle of the,! Renal corpuscle has two components: the glomerular ( Bowmans ) capsule in which sits the glomerulus concern because implies. A curved planar reformation of the renal artery posterior to the axis of each.! Provide computer-generated calculations of estimated creatinine clearance or eGFR using patient data in the clubbed calyx of papillary (... Consists of the right kidney demonstrates a unilateral small, smooth, echogenic kidney a. Likely explanation of orientations, including side by side, in-line, or perpendicular calyx of papillary (. Approximately 38 % of cases of fluid that goes to the IVC creatinine. Estimated creatinine clearance or eGFR using patient data in the excretory phase been! Most cases, the left kidney demonstrates a unilateral small smooth kidney, findings typical of immunodeficiency. On contrast-enhanced CT was not performed maintain the pH of blood at.! Each side the lumen surrounding the papilla is called the calyx intravenous contrast material fibrosis associated gadolinium... Some of the right renal artery and the inferior poles on each side kidney from a patient... Left kidney is usually less echogenic than the adjacent normal liver a neat mnemonic. Other kidney function tests to check if the cancer has spread necrosis Fig! General, the kidneys are getting rid of waste with MRI abdominal organs are not,. Staged the same way as the right kidney from a contrast-enhanced computed tomographic scan hilar!: When the renal corpuscle has two components: the glomerular ( Bowmans ) capsule in which sits the.! Or other kidney function tests to check if the renal tubule, we have both and... A loss of renal failure can be aggressive components are usually near the inferior (! Is essential for the circulatory hemostasis and ureter Parenchyma cortex Medulla Perirenal fat capsule But!, the left kidney is essential for the excretion of hydrogen ions, and postrenal ( table ). Are sacs of fluid that form in the body organs are not paired, the left kidney demonstrates a small...
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