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1 in collaborazione con Close window to return to IVIS RICHIESTO ACCREDITAMENTO SOCIETÀ CULTURALE ITALIANA VETERINARI PER ANIMALI DA COMPAGNIA SOCIETÀ FEDERATA ANMVI organizzato da certificata ISO 9001:2000 INFORMATION SCIVAC Secretary Palazzo Trecchi, via Trecchi 20 Cremona Tel. (0039) Fax (0039) commscientifica@scivac.it

2 In: 50 Congresso Nazionale Multisala SCIVAC Imaging of the Urinary Tract parts 1 & 2 Anne Bahr, DVM, MS, Diplomate, ACVR Assistant Professor Texas A&M University, College Station, Texas USA Normal Abdominal Structures Kidneys The kidneys are located in the retroperitoneal space. They are best seen on the VD view and are measured compared to the length of L2. In the dog, normal kidneys may be times the length of L2 and in the cat times the length of L2. The kidneys should be evaluated for disparity of size and margination as well as changes in opacity. The kidneys are normally at the level of T13-L4. The right kidney is usually more cranially located in the dog. In the cat, the kidney may be pendulous. Diseases of the Kidneys Uniform increases in kidney size may be due to: Compensatory Hypertrophy Neoplasia Hydronephrosis FIP Perirenal pseudocysts Acute pyelonephritis Focal increases in kidney size may be due to: Neoplasia Subcapsular hemorrhage Hematoma Abscess Renal Cysts Decrease in kidney size may be due to: Chronic pyelonephritis Chronic infarcts Cortical Hypoplasia Chronic Progressive Renal Disease Normally the kidneys should be soft tissue opacity and surrounded by the retroperitoneal fat. An increase in opacity is usually associated with nephroliths or nephrocalcinosis. Loss of visualization of the kidneys may be due to fluid accumulation within the retroperitoneal space. Normal Abdominal Structures Ureters The ureters not normally seen radiographically. Anatomically, the proximal ureter is retroperitoneal while the most distal portion is peritoneal in location. The only way to evaluate the ureters is with contrast radiography Contrast Radiography of the Kidneys/Ureters Excretory Urogram Indications with the advent of ultrasound most uses of the EU to evaluate the kidneys has been replaced. However, it is still useful to evaluate the size and location of the kidney if ultrasound

3 is not available or if there is difficulty evaluating the kidneys on ultrasound. The most common indication for an EU today is to diagnose the location of an ectopic ureter. Technique Clinical dehydration is the main contraindication. Prepare animal as for other contrast studies (NPO, enemas). Survey radiographs should be obtained immediately prior to beginning study. Adminster 400mg/lb of iodinated contrast media as a bolus intravenously. Immediate radiographs (2 views) and then views at 5, 10, 20 and 40 minutes should be obtained. These times can be adjusted depending on the goal. Visualization of contrast within the kidneys requires: renal blood flow, functional glomeruli, tubular reabsorption, and a patent collecting system. Interpretation The kidneys can be evaluated for size, shape, opacity, etc during the nephrogram phase. The ureters will be visualized during the pyelogram phase. The are usually 1-2 mm in diameter and should have peristalsis present. Therefore, the entire length of the ureter will not be visualized at any one time. Pneumocystography may be helpful in determining the location of the ureteral termination. Normal Abdominal Structure Urinary Bladder Survey radiographs are useful only for evaluating bladder position, opacity, shape and size. However, it may be necessary to perform a contrast study to complete the evaluation. The bladder is divided into 3 areas vertex, body, neck. The trigone is the dorsal aspect of the neck. Diseases of the Urinary Bladder Changes in bladder position may be due to herniation or displacement due to enlargement of adjacent viscera. Changes in opacity is normally due to the presence of calculi. Radiopaque calculi include those that contain calcium or phosphorus. A decrease in opacity can be seen with air in the lumen from iatrogenic causes or air in the wall from emphysematous cystitis. Emphysematous cystitis is often associated with diabetes mellitus or hyperadrenocorticism. Changes in size is subjective but can be due to obstruction, an inability to eliminate. A complete lack of visualization of the urinary bladder can be due to rupture or just an empty bladder. Contrast Studies of the Urinary Bladder There are 3 types of studies Negative, positive and double contrast cystograms. A negative contrast cystogram is usually only to determine the position of the urinary bladder. The positive contrast cystogram is used to determine the integrity of the urinary bladder. The double contrast cystogram is used to evaluate the mucosal and luminal areas of the urinary bladder. The latter has recently been replaced with the use of ultrasound. Technique Negative contrast cystogram. This is fast and inexpensive. Position a catheter within the urinary bladder and distend with either room air or CO2. CO2 is considered ideal as it is less likely to cause embolism. Distend the urinary bladder until it palpates turgid (take care not to over distend) and then obtain radiographs. Positive Contrast Cystogram Similar to the Negative Contrast Cystogram except use iodinated contrast media. Often can dilute iodinated contrast by 50-75%. Distend urinary bladder until it is turgid. This is critical if interested in leakage as small holes may not leak until the bladder is distended. Double Contrast Cystogram Position a catheter in the urinary bladder. Remove as much urine as possible. Instill 5-15 mls of iodinated contrast and then instill negative contrast (air or CO2) until the bladder is distended. Terminate the injection if back pressure if felt. Obtain radiograph in RL, LL, VD, DV in order to distribute the contrast puddle to all areas of the bladder. Evaluation Double Contrast Cystogram The mucosal surface and wall can be evaluated. The wall should be thin and uniform. Thickening of the cranial ventral wall is often associated with cystitis. Neoplasia is typically found in the trigone. However, inflammation or neoplasia can cause changes in any part of the bladder. The lumen can be evaluated and the following table details these findings.

4 Filling Defect Shape Borders Location Air Bubbles Round Smooth Periphery of contrast puddle Calculi Round to Irregular Indistinct Center of contrast puddle Blood Clot Irregular Irregular to indistinct In the contrast puddle or near the wall Ultrasonographic evaluation of the Kidneys Examination technique usually requires a 5-7 MHz sector transducer for most dogs and cats. A linear transducer may be used in small animals. The kidney cortex is typically of similar or slightly less echogenicity than the liver. It should be noted that in some fat cats, the cortex may be more echogenic due to fatty infiltration which is not pathologic. The medulla is typically hypoechoic relative to the cortex and there should be a distinct corticomedullary junction. The medulla is separated from the cortex by the diverticula and interlobar vessels. The renal papillae may be surrounded by fat in some some animals creating an echogenic focus in the region of the pelvis. Due to the shape of the kidney, edge shadow artifact may occur which should not be confused with mineralization. The size of the kidney can be measured using ultrasound however no known normal values are available for dogs. Cats should have kidneys that are at least cm in length in a mid sagittal plane. One of the common changes that are seen is increased echogenicity of the kidney cortex. This is commonly found in kidneys with chronic progressive renal disease. Other abnormalities such a inflammation, infection or mineralization can also cause this. In some animals a distinct, echogenic line can be seen at the corticomedullary junction (known as the rim sign). There is no clinical significance applied to this finding. Decreased echogenicity of the cortex can also occur usually due to cystic formations. This may occur with chronic renal disease but may also be a syndrome in itself as is seen in certain breeds of cats. Care should be taken to not mistake a hypoechoic medulla for cysts. These are differentiated based upon location (cortex vs medulla) as well as the presence of through transmission. This is a sonographic artifact that is used as an aid in diagnosis. Through transmission occurs because the ultrasound beam is relative less attenuated when it passes through fluid filled structures than by the surround soft tissues. This creates echoes with greater returning energy and thus the computer assigns them a higher echogenicity. Therefore, cystic structures (such as the gall bladder or renal cortical cysts) will have increased echogenicity deep to them indicating they are fluid filled. Neoplasms of the kidney may be echogenic, isoechoic or hypoechoic. The mass usually will deform the architecture of the kidney. Biopsy is necessary to determine the etiology of the mass. Abnormalities of the collecting system and ureters are commonly evaluated using ultrasound. The normal canine proximal ureter should not be more than about 2 mm in diameter. Mild pelvic dilation (pyelectasia) is more easily seen on a mid transverse view of the kidney. This will appear as a anechoic v-shaped area adjacent to the renal papillae. Pyelectasia most commonly is associated with diuresis, pyelonephritis or early/partial obstruction. Moderate to severe dilatation of the renal pelvis is termed hydronephrosis and is usually associated with obstruction. This can be seen as an anechoic area in the center of the kidney. The renal papillae may atrophy and be blunted. Calculi may cause obstruction of the collecting system and are seen as hyperechoic shadowing foci usually in the pelvis or proximal ureter. Mineralization within the diverticulae is common and usually doesn t cause obstruction. Ultrasound of the urinary bladder It is important that the urinary bladder be distended when evaluating it with ultrasound. Common problems which can be identified on ultrasound includes changes in bladder wall thickness, mass lesions, foreign bodies, calculi, blood clots, diverticula, ectopic ureters and ureteroceles. In addition, the bladder can be used as an acoustic window to evaluate the prostate, uterus and sublumbar region. A small convex mass can sometimes be seen in normal animals in the trigone known as the ureteral papillae (where the ureters open into the bladder). Usually, a 7-10 MHz transducer is needed to evaluate the urinary bladder. A common artifact that is seen when imaging the urinary bladder is the side lobe or grating lobe artifact. This occurs because there is a very echogenic structure (usually gas in the colon) next to the bladder. Echoes from the side lobes which normally don t contribute to formation of the image when they are returning from the colon will create echogenic lines within the lumen of the urinary bladder due to inaccurate placement by the computer. All echoes which return to the

5 transducer are assumed to be created by the main beam. Thus, this artifact can be eliminated by angling the transducer to prevent interaction with the colon or more typically by decreasing the overall gain thus decreasing the gain of the side lobes. The urinary bladder should be scanned in two planes. In some instances, ureteral jets can be identified at the ureteral papillae particularly when using color flow Doppler. It is typically not difficult to evaluate the cranial bladder wall which is parallel to the ultrasound beam. This often creates an anechoic area in the wall due the inability of the beam to generate echoes in a structure that is parallel with it. Bladder wall measurements are best made along the dorsal surface. A standoff pad may be necessary to measure the ventral bladder wall to eliminate the bang artifact. The bladder wall thickness varies with the amount of distension. One study suggested that the wall should not be thicker than 2.3 mm in small bladders. However, personal experience suggests that this may not hold true. If the bladder is small and measurement is critical, reimage when the bladder is more distended. This can be accomplished by waiting, administering a diuretic or by instilling saline via an urinary catheter. A common abnormality that causes a change in the thickness of the urinary bladder is cystitis. This is typically seen in the cranial portion of the bladder and may cause asymmetric thickening (it is thinner near the neck) as well as mucosal irregularity. Remember that ultrasound can not differentiate cystitis from other infiltrative diseases such as neoplasia. Calculi can be readily identified using ultrasound. They typically will be echogenic structures which cast shadows deep to them. The ability to see calculi is dependent upon their size, the frequency of transducer being used as well as positioning of focuses within the image. If the calculi is smaller than the ultrasound beam, then it may not be seen. Use the highest frequency transducer possible when looking for small calculi. The most common neoplasm found in the urinary bladder is transitional cell carcinoma. This is typically seen as thickening or mass formation in the trigone region. However, it can be seen in any location within the urinary bladder. TCC often originates from the urethra and so careful evaluation of the neck and proximal urethra should be performed if possible. In many animals, the urethra may be difficult to evaluate due to its intrapelvic location. Sector/vector transducers are often helpful with this as it is possible to point the probe under the pubis. Intrarectal probes are also available and my provide a better window for evaluation of this area. Of course, other types of tumors may be seen such as fibrosarcoma or rhadomyosarcoma etc. The tumor type cannot be determined by ultrasound. The urinary bladder is found ventral to the colon (and uterus in females). The wall is normally thin (less than 2-3 mm) and should have anechoic contents. In cats, the urine may contain some echoes, which may be clinically insignificant (possible crystals). Renal Scintigraphy Most imaging modalities provide morphologic information regarding the kidneys. Diagnoses are grouped based upon changes in kidney size, shape, margination and opacity. However, survey radiographs are limited in patients with little retroperitoneal fat, excessive ingesta, or perirenal fluid accumulation. Excretory urography further defines the morphology of the renal cortex and collecting system. Qualitative assessment of renal function is possible on an EU but it is limited in patients with azotemia. Functional information can be obtained through estimation of glomerular filtration rate which is directly proportional to the number of functional nephrons. The gold standard for measuring GFR is inulin clearance. Inulin is an ideal marker for measuring GFR since it is metabolically inert, it is filtered by the glomerulus and has no tubular secretion or absorption. The technique for measuring inulin clearance is labor-intensive and is not suited for routine clinical evaluations. Serum creatinine and BUN concentrations provide an estimation of GFR but have poor sensitivity in that they do not become elevated until there is significant renal insufficiency. Blood urea nitrogen (BUN) is filtered in the glomerulus and is then reabsorbed in the tubules with the amount reabsorbed dependent on tubular flow. Both prerenal and post renal factors can result in increases in BUN. of the functioning renal mass is lost and therefore a poor screening method for detection of renal injury. Serum creatinine concentration is less dependent on non-renal factors than BUN concentration. Creatinine is produced by muscle metabolism and is excreted by the kidneys almost entirely by glomerular filtration but with some tubular secretion. Serum creatinine concentrations are determined by the volume of creatinine distribution, the rate of production from the muscle, the rate of excretion and the noncreatinine chromogen contribution. Serum creatinine concentration can be elevated with dehydration or renal

6 failure. False positive results can occur due to measurement of the non-creatinine chromagens when the alkaline picrate method is used. GFR estimation via scinitgraphy is a clinically useful tool to more accurately evaluate renal function. The study takes less than 10 minutes to complete. The radiopharmaceutical that is used is 99mTcdiethylenetriamepentacetic acid (DTPA). It is excreted exclusively via glomerular filtration rate. A regression formula is used to estimate the GFR based upon the percent dose uptake of the 99mTC -DTPA within the kidney between 1 and 3 minutes after injection. An advantage of this technique over Inulin clearance is that the GFR of each individual kidney may be estimated. Indications for GFR scintigraphy: evaluate global renal function in terms of GFR, subclinical renal insufficiency, response to therapy,evaluate kidney function prior to renal insult (chemotherapy, pre radioiodine therapy),evaluate individual kidney function (imaging studies only), prior to nephrectomy, prior to nephrotomy References: Berry CR, Daniel GB, eds. Handbook of Veterinary Nuclear Medicine. North Carolina State University, Thrall DE, ed. Textbook of Veterinary Diagnostic Radiology, 4 th ed. Philadelphia, WB Saunders, Nyland TG and Mattoon JS, eds. Small Animal Diagnostic Ultrasound, 2 nd ed. Philadelphia, WB Saunders, This manuscript is reproduced in the IVIS website with the permission of the Congress Organizing Committee