Elizabeth Huynh VCA West Coast Specialty and Emergency Animal Hospital, Fountain Valley, CA, USA See Chapter 20. Normal renal size does not rule out renal disease. Renal parenchymal diseases such as toxicity, amyloidosis, glomerulonephritis, acute nephritis, and pyelonephritis may be present without changes in renal size. Renomegaly (>3.5 times the length of L2 in dogs; >3.0 times the length of L2 in cats) can be diagnosed using abdominal radiographs. Severe unilateral or bilateral renomegaly causes peripheral displacement of adjacent abdominal contents. Renomegaly may be associated with parenchymal, capsular, or renal pelvic abnormalities. Usually, additional studies, using intravenous contrast medium or ultrasound, are needed to further assess the underlying cause of renomegaly. Differentials for smoothly marginated renomegaly include hydronephrosis, perinephric pseudocyst (Figure 27.1), lymphomsa (may be bilateral) (Figure 27.2), amyloidosis (usually mild renomegaly), compensatory hypertrophy (Figure 27.3), renal hypertrophy secondary to portosystemic shunts (usually mild and more often seen in dogs than cats) (Figure 27.4), acromegaly, acute nephritis, toxicity, or acute renal failure (mild renomegaly). Differentials for irregularly marginated renomegaly include neoplasia (primary or metastatic) (Figure 27.5), focal renal cyst, polycystic kidney disease (Figure 27.6), feline infectious peritonitis, abscess (Figure 27.7), or hematoma. Excretory urography is used to diagnose parenchymal and ureteral changes of the kidneys as well as providing information regarding renal function. Diffuse and focal renal parenchymal diseases cause variable changes in the nephrogram and pyelogram phases. The contrast study may be normal if renal function is sufficient with minimal architectural changes. If renal function is poor, there may be decreased opacification of the nephrogram and/or pyelogram phase. Differentials for enlarged, unopacified kidneys include hydronephrosis, neoplasia, inflammation, severe cystic disease, renal trauma, and renal vein thrombosis. Neoplasia, cysts, abscesses, infarctions (Figure 27.8), and hematoma may result in focal or multifocal unopacified disruptions of the nephrogram phase. FIGURE 27.1 Left lateral (A) and VD (B) abdominal radiographs of a cat with asymmetrically normal sized kidneys (arrowheads). Sagittal plane ultrasound image (C) of a small right kidney in the same cat with a large perinephric pseudocyst. FIGURE 27.2 Right lateral (A) and VD (B) abdominal radiographs of a cat with bilateral renomegaly (arrowheads), diagnosed with renal lymphoma. FIGURE 27.3 Right lateral abdominal radiograph of a cat with a small right kidney (white arrowheads) and left renomegaly (black arrowheads), consistent with compensatory hypertrophy. FIGURE 27.4 Right lateral (A) and VD (B) abdominal radiographs of a dog with bilateral renomegaly (arrowheads), consistent with renal hypertrophy secondary to a congenital extrahepatic portosystemic shunt. Note the microhepatia and cranial displacement of the gastric axis on the right lateral radiograph. FIGURE 27.5 Right lateral (A) and VD (B) abdominal radiographs of a dog with unilateral irregularly marginated renomegaly (arrowheads), consistent with primary malignant carcinoma. FIGURE 27.6 Right lateral (A) and VD (B) abdominal radiographs of a cat with bilateral irregularly marginated renomegaly (arrowheads), consistent with polycystic kidney disease. FIGURE 27.7 Left lateral (A) and VD (B) abdominal radiographs of a dog with unilateral irregularly marginated soft tissue opaque mass effect contiguous with the cranial pole of the left kidney (arrowheads), consistent with a renal abscess. Nonspecific changes associated with renomegaly can be seen as diffuse renal cortical hyperechogenicity on ultrasound. Considerations for these changes include glomerulonephritis, interstitial nephritis, acute tubular necrosis, endstage renal disease, lymphoma, feline infectious peritonitis, hypercalcemic nephropathy, pyelonephritis, congenital renal dysplasia, and renal diverticular mineralization. In more progressive renal disease, decreased or loss of renal corticomedullary distinction (Figure 27.9) is noted and is caused by increased medullary and cortical echogenicity. A medullary rim sign is a thin hyperechoic band of the outer renal medulla (Figure 27.10), which can be seen in both normal and diseased kidneys (i.e., hypercalcemic nephropathy, chronic interstitial nephritis, and acute tubular necrosis) [1–5]. Acute renal failure associated with ethylene glycol toxicity usually results in severely hyperechoic renal cortices with or without hyperechoic renal medullae [5]. Renal hypertrophy from the loss of contralateral renal function or congenital portosystemic shunts should appear normal in echogenicity and architecture. More severe generalized renomegaly can occur with diffuse infiltrative neoplasia, such as lymphoma, or feline infectious peritonitis. Lymphoma often results in bilateral renal changes, pyelectasia, loss of corticomedullary distinction, renomegaly, renal deformity, hypoechoic lesions, and, rarely, hyperechoic lesions [6]. In cats, hypoechoic subcapsular thickening is associated with renal lymphoma [7] (Figure 27.11); this may represent neoplastic infiltration into the subcapsular region. Subcapsular thickening is also seen with renal carcinoma and feline infectious peritonitis [8]. FIGURE 27.8 Excretory urogram. Collimated VD abdominal radiograph of a dog with a triangular‐shaped, unopacified disruption of the nephrogram phase (arrowhead), consistent with a renal cortical infarction. FIGURE 27.9 Sagittal (A) and transverse (B) plane ultrasound images of a small left kidney of a cat with chronic renal disease, further characterized by loss of corticomedullary distinction, mild pyelectasia seen on the transverse plane image (between the calipers), and a small renal diverticular mineralization seen on the sagittal plane image (between the calipers). FIGURE 27.10 Sagittal plane ultrasound image of the left kidney of a dog with a medullary rim sign with no renal dysfunction. Renal cysts, abscesses, hematomas, or neoplasia causes irregular renomegaly. Polycystic kidney disease is a genetic disorder where normal renal tissue is displaced by multiple cysts (Figure 27.12). This is typically seen in Persian cats or Persian mixed‐breed cats and has been reported in cairn and bull terrier dogs [9–12]. Cystadenocarcinomas (Figure 27.13) in German shepherd dogs are associated with dermatofibrosis. On ultrasound, they may appear as cavitated, complex masses [13, 14]. A few cysts are usually incidental, benign, round, variably sized, anechoic lesions with distal acoustic enhancement on ultrasound. Renal abscesses and hematomas are rare but result in focal renal changes. Abscesses may occur secondary to regional infection or hematogenous spread of bacteria. Renal abscesses (Figure 27.14) have variable ultrasonographic appearances but are often seen as cavitated lesions with thick, irregular walls. Intralesional hyperechoic shadowing gas or reverberation artifact can be seen, secondary to gas‐producing bacteria. Parenchymal (Figure 27.15) or subcapsular hematomas may be caused by trauma, coagulopathy, or renal biopsy. Hematomas can also occur within the renal pelvis, resulting in obstructive hydronephrosis. Abscesses and hematomas may have identical ultrasonographic appearances to renal neoplasia. FIGURE 27.11 Sagittal plane ultrasound images of the left (A) and right (B) kidneys of a cat with renal lymphoma. Note the enlarged, irregularly marginated kidneys with hyperechoic renal cortices, decreased corticomedullary distinction, multifocal hypoechoic nodules, and hypoechoic subcapsular thickening. FIGURE 27.12 Sagittal (A) and transverse (B) plane ultrasound images of the left kidney of a cat with polycystic kidney disease. The left kidney is enlarged and there are numerous, amorphous and round, anechoic renal cortical cysts, and severely dilated renal pelvis (between the calipers). FIGURE 27.13 Sagittal plane ultrasound image without color Doppler (A) and with color Doppler (B) of the kidney of a German shepherd with a cystadenocarcinoma. FIGURE 27.14 Sagittal plane ultrasound image of the kidney of a dog with a renal abscess. Note the cavitated lesion with a thick irregular wall and echogenic intraluminal material. Although neoplasia (i.e., lymphoma) may cause generalized renomegaly, it can also cause focal or multifocal enlargement. Epithelial neoplasms, such as carcinomas, are the most common primary renal neoplasm in the dog; a mass can be seen at either the cranial or caudal pole of the kidney. While these are usually unilateral, both kidneys can be affected. On ultrasound, renal carcinoma (Figure 27.16) may be hypoechoic, hyperechoic, or complex, completely obliterating the normal renal architecture [15]. Renal metastatic lesions cause hyperechoic, hypoechoic, or isoechoic masses. Hemangiosarcoma, osteosarcoma, melanoma, mast cell tumor, pulmonary carcinoma, mammary gland, and gastrointestinal tract have all been reported to metastasize to the kidneys. FIGURE 27.15 Transverse plane ultrasound image of the kidney of a dog with a well‐defined, hypoechoic, renal hematoma (arrowheads). FIGURE 27.16 Sagittal plane ultrasound image of the kidney of a dog with renal carcinoma. There is a large, poorly delineated, heterogeneous mass of the left kidney and no normal renal architecture is appreciated. Subcapsular or perirenal disease usually causes smoothly marginated generalized renomegaly or, less commonly, irregularly marginated renomegaly. Perinephric pseudocysts (Figure 27.17) have been reported most often in cats and result in focal fluid accumulation around one or both kidneys [16]. The development of these cysts is unknown. On ultrasound, the kidney is surrounded by a thin, round, anechoic fluid‐filled structure. Renal hyperechogenicity may be artifactual secondary to acoustic enhancement from the fluid or secondary to diffuse nephropathy. Small renal sizes (<2.5 times the length of L2 in dogs; <2 times the length of L2 in cats) can usually be diagnosed using abdominal radiography. Differential diagnoses for small, smoothly marginated kidneys include renal hypoplasia, amyloidosis, and endstage renal disease. Differential diagnoses for small, irregularly marginated kidneys include chronic or endstage renal disease (Figure 27.18). FIGURE 27.17 Sagittal plane ultrasound image of the kidney with a perinephric pseudocyst in a cat. FIGURE 27.18 Right lateral (A) and VD (B) abdominal radiographs of a cat with bilaterally small and irregular kidneys, representing chronic kidney disease. Small kidneys may be caused by congenital renal disease (which is present at birth), familial renal disease (which may result in chronic renal failure at a young age), or acquired chronic renal disease. Small kidneys secondary to chronic renal disease may be irregular in margination due to cortical infarctions. Ultrasound of the affected kidney typically shows a small, irregular, hyperechoic kidney with decreased corticomedullary distinction. Chronic renal cortical infarctions (Figure 27.19) appear as hyperechoic, wedge‐shaped, cortical lesions [17]. To assess the ureters and further assess the urinary tract using radiography, excretory urography may be helpful. Indications for excretory urography include trauma to the urinary tract, hematuria, suspicion for ectopic ureters, retroperitoneal mass effect, or decreased retroperitoneal serosal detail. Excretory urography uses intravenous positive contrast medium, in the form of nonionic iodinated contrast medium, to opacify the urinary tract. Uncommon adverse effects to intravenous iodinated contrast medium include nausea, vomiting, hives, hypotension, and contrast medium‐induced anuric renal failure. Contraindications for excretory urography include azotemia, anuric renal failure, dehydration, hypotension, or known hypersensitivity reactions to iodinated contrast medium. FIGURE 27.19 Sagittal (A) and transverse (B) plane ultrasound images of the chronic kidney disease of a cat. There are well‐defined, hyperechoic, triangular‐shaped, chronic renal cortical infarctions. The left kidney is also small and exhibits decreased corticomedullary distinction. FIGURE 27.20 Excretory urography. Survey right lateral abdominal radiograph (A) and right lateral abdominal radiograph at the time of intravenous administration of contrast medium (B) denoting a normal nephrogram phase of a dog. Note the contrast medium uptake in the renal cortex when compared to the survey abdominal radiograph. This patient sustained a vehicular trauma. There is decreased retroperitoneal and peritoneal serosal detail, prompting this study to rule out uroperitoneum and uroretroperitoneum. In addition, there is also mild pneumothorax, pelvic fractures, right coxal luxation, and multiple caudal lumbar vertebral fractures. In preparation for a diagnostic excretory urogram, the patient should be fasted for at least 12 hours before the study. An enema should be performed to avoid additional superimposition of colonic feces over the urinary tract. Baseline bloodwork should also be performed to ensure that the patient has adequate renal function. Survey collimated abdominal radiographs are recommended prior to excretory urogram to ensure adequate radiographic exposure and efficacy of the enema. An intravenous catheter should be placed. Sedation or general anesthesia is recommended. Iodinated contrast medium is administered intravenously as a bolus injection at 600–700 mgI/kg of body weight. Ventrodorsal (VD) and right lateral radiographs should be performed immediately after contrast medium administration. Oblique radiographs to further assess the ureters can also be performed. Radiographs should be repeated after 5, 20, and 40 minutes or until a diagnosis is reached. To evaluate the renal arteries, VD radiographs should be taken 5–7 seconds after the bolus injection of contrast medium. At 5–7 seconds after contrast medium administration, the renal arteries are opacified. Excretory urogram can be divided into three phases: (i) nephrogram phase, (ii) pyelogram phase, and (iii) cystogram phase. The nephrogram phase (Figure 27.20) begins after 10 seconds and lasts up to 2 minutes, with peak opacity at 10–30 seconds. This phase occurs when the contrast medium arrives in the glomerular vessels and filters into the nephron, leading to uniform opacification of the renal parenchyma. Initially, the renal cortex can be more opaque than the medulla. The intensity and duration of the opacity of the kidneys in this phase depend on the dose of contrast medium, renal perfusion, glomerular filtration of the contrast medium, tubular resorption of water, and patency of the renal outflow tract. The renal parenchymal opacity should continue to decrease over time, but approximately 25% of normal dogs still have a detectable nephrogram 2 hours after the initial time of the study. As the nephrogram phase fades, the pyelogram phase begins. FIGURE 27.21 Excretory urography. Right lateral abdominal radiograph taken 5 minutes after intravenous administration of contrast medium in the same dog denoting a normal pyelogram phase. Note the decreased renal cortical contrast enhancement and increased renal medullary contrast enhancement in addition to renal pelvic and ureteral contrast filling. There is also mild contrast filling within the urinary bladder, representing part of the cystogram phase. The pyelogram phase (Figure 27.21) occurs when contrast medium collects in the collecting system as the nephrogram phase fades. The pyelogram phase can last for ≥2 hours after contrast medium injection. If renal function is normal, the collecting system is persistently more opaque than the renal parenchyma. The normal renal pelvis is curvilinear in shape, measuring ≤2 mm in width. The renal diverticula may be seen in some dogs and cats and are thin, sharply marginated, spikes radiating from the pelvis, measuring ≤1 mm in width. In some dogs, the renal diverticula are not well defined. The diverticula in cats are usually more prominent. During this phase, contrast medium fills the ureters. The normal ureteral diameter is variable in size due to intermittent ureteral peristalsis, but should not measure >3 mm in width. The caudal aspect of the ureters course in a cranial direction before entering the urinary bladder at the cranial aspect of the trigone. The cystogram phase (Figure 27.22) occurs when a variable volume of contrast medium accumulates in the urinary bladder. An excretory urogram provides a crude assessment of renal function, although only 5% of renal function is needed for excretion of iodinated contrast media. FIGURE 27.22 Excretory urography. Right lateral abdominal radiograph taken 10 minutes after intravenous administration of contrast medium in the same dog denoting a normal cystogram phase. The lack of nephrogram and pyelogram phases with a history of trauma indicates renal avulsion (Figure 27.23). A poor initial nephrogram that fades immediately is usually due to an insufficient dose of contrast medium or primary anuric renal failure. A poor initial nephrogram followed by persistent opacity may represent severe generalized renal disease. A poor initial nephrogram followed by increasing opacity may be caused by prior systemic hypotension, acute extrarenal obstruction, or renal ischemia. A good initial nephrogram followed by persistent or increasing opacity may indicate systemic hypotension or contrast‐induced renal failure, acute renal tubular necrosis, or acute renal obstruction. The opacity of the pyelogram phase may be decreased in the face of renal failure, because of increased urine volume and decreased concentrating ability. Percutaneous positive‐contrast pyelography introduces positive contrast directly into the renal pelvis, avoiding any potential adverse systemic reactions. This technique does not allow assessment of the renal parenchyma but rather assessment of the renal pelvic and ureteral size, shape, diameter, and patency. Indications for this procedure include unilateral hydronephrosis and hydroureter (Figure 27.24) to determine the degree and location of any ureteral obstruction. In preparation for a diagnostic percutaneous positive‐contrast pyelography, the patient should be fasted for at least 12 hours before the study. An enema should be performed to avoid additional superimposition of colonic feces over the urinary tract. Survey collimated abdominal radiographs are recommended to ensure the adequate radiographic exposure and efficacy of the enema. An intravenous catheter should be placed. Sedation or general anesthesia is recommended. A 25 gauge spinal needle is inserted through a thin portion of the renal cortex into the dilated pelvis under ultrasound guidance. The large hilar and interlobar vessels should be avoided. A volume of urine is removed, depending on the degree of hydronephrosis, and an equivalent of one‐half of the removed volume of nonionic iodinated contrast medium is slowly administered. Renal pelvic and ureteral filling can be visualized using fluoroscopy, if available, followed by VD and lateral abdominal radiographs. FIGURE 27.23 Excretory urography. Ventrodorsal abdominal radiograph of a dog with a traumatic abdominal wall hernia and herniation of small intestine within the subcutaneous tissues. There is a normal nephrogram phase of the left kidney (A) and normal pyelogram phase of the left kidney (B). There is no normal nephrogram or pyelogram phase of the right kidney, representing right renal avulsion. FIGURE 27.24 Right lateral (A) and VD (B) radiographs after percutaneous antegrade positive‐contrast pyelogram of a cat with bilateral hydronephrosis and hydroureter. There is mild iatrogenic retroperitoneal and peritoneal contrast medium extravasation. The most common complications are leakage of contrast medium from the renal pelvis secondary to inadvertent needle puncture, and capsular leakage at the site of needle insertion. Subcapsular hemorrhage and renal pelvic hemorrhage can be a serious complication. Abnormalities of the collecting system can occur secondary to pyelonephritis or hydronephrosis. The abnormalities are best visualized with intravenous contrast medium studies or ultrasonography. FIGURE 27.25 Sagittal (A) and transverse (B) plane ultrasound images of the right kidney of a cat with pyelonephritis. Note the distended renal pelvis with anechoic fluid (between the calipers). FIGURE 27.26 Transverse plane ultrasound image of a kidney at the level of the kidney (A) and proximal ureter (B) of a dog with obstructive hydronephrosis secondary to hyperechoic shadowing proximal ureteral calculi. Pyelonephritis (Figure 27.25) can result in pyelectasia (up to >3 mm is considered abnormal) [18] and mild proximal ureteral dilation. Ultrasound characteristics of pyelonephritis include hyperechoic renal cortices, decreased corticomedullary distinction, along with renal pelvic and proximal ureteral distension [19]. Hydronephrosis results in smoothly marginated, unilateral or bilateral renomegaly on abdominal radiographs. Depending on renal function, intravenous contrast medium administration usually causes contrast medium‐dilated renal pelvis and diverticula. In severe hydronephrosis, there may be only a small rim of cortical tissue surrounding the markedly dilated renal pelvis. Ultrasonography provides excellent visualization of hydronephrosis (Figure 27.26). If the ureter is also dilated, it should be followed caudally to determine the cause of obstruction. Common causes of obstructive hydronephrosis include ureteral calculi, urinary bladder trigone neoplasia, ureteral stricture secondary to trauma or chronic ureteritis, blood clots following renal biopsy, or a combination of these. Common causes of mineralization of the kidneys include renal diverticular mineralization and nephrolithiasis (renal pelvic calculi) (Figure 27.27) that may extend into the proximal ureter. Only mineral opaque calculi (i.e., phosphates or oxalates) are visible on abdominal radiographs. Ultrasonography can detect both radiolucent and radiopaque calculi both appearing hyperechoic with or without distal acoustic shadowing. If obstructive ureteral calculi are present, anechoic fluid dilation of the cranial ureter can be seen. FIGURE 27.27 Transverse plane ultrasound image of a kidney of a cat with nephrolithiasis. Note the hyperechoic shadowing calculus in the renal pelvis. FIGURE 27.28 Sagittal (A) and transverse (B) plane ultrasound images of the left kidney of a cat with hyperechoic shadowing, renal diverticular mineralization, decreased corticomedullary distinction, and pyelectasia. Renal diverticular mineralization (Figure 27.28) is characterized by dystrophic parenchymal mineralization and may be difficult to differentiate from nephrolithiasis on radiography or ultrasonography. Both conditions cause mineral opacities on radiographs and hyperechoic foci on ultrasound. Unless there is urine dilation of the affected ureteral segment, differentiation between renal diverticular mineralization and small nephrolithiasis may not be possible. Other causes of dystrophic mineralization include hematomas, cysts, abscesses, granulomas, and neoplasms. Acute renal failure may result in perirenal retroperitoneal fluid (Figure 27.29). This is often subtle on radiographs. Ultrasonographically, the volume of fluid may only be mild to moderate. The fluid may accumulate adjacent to a failing kidney with unilateral ureteral obstruction, or in a patient without systemic signs of renal failure (azotemia). The amount of fluid does not correlate with the severity of renal failure. Often the fluid extends into the peritoneal space. The pathogenesis may involve excess hydrostatic pressure or vasculitis of capsular vessels in the affected kidney. FIGURE 27.29 Sagittal plane ultrasound image of a kidney of a cat with acute renal failure. There is generalized renomegaly, loss of corticomedullary distinction, and mild anechoic perirenal effusion. Renal secondary hyperparathyroidism, now known as chronic kidney disease‐mineral and bone disease (CKD‐MBD) [20], is a common complication of chronic kidney disease in dogs and cats and can manifest in the skeletal system with visible radiographic changes [21]. The skull and mandible show the earliest and most dramatic changes, with marked demineralization (Figure 27.30). The teeth may be increased in mineral opacity when compared to the other cranial osseous structure because of severe mineral loss in the lamina dura [22]. The changes are most marked and occur most rapidly in the immature patient. Metastatic calcification is a sequela of chronic renal disease and occurs when there is an elevated calcium:phosphate ratio. Mineralization is most prominent in the stomach (uremic gastropathy) (Figure 27.31), arteries, joints, and kidneys, although mineral opacities can also be seen in the myocardium, lungs, and liver. Mineral opaque ureteral calculi can often be visualized on abdominal radiographs. Calcium oxalate calculi are the most common type of ureteral calculi in cats, with both calcium oxalate and struvite occurring in dogs. Both types are routinely mineral opaque and well visualized. However, additional studies may be needed if ureteral mineral opacities are seen, to determine whether they are real. Mineral opacities in the colon superimposed on the kidneys or ureters, as well as the end‐on deep circumflex iliac vessels, can be mistaken for ureteral calculi (Figure 27.32). Mineral opaque ureteral calculi are most easily visualized as a discrete round or ovoid mineral opacity within the retroperitoneum on lateral abdominal radiographs. Superimposition of gas and feces on the VD projection may obscure the visualization of calculi. FIGURE 27.30 Lateral (A) and DV (B) skull radiographs of a young dog with renal secondary hyperparathyroidism. Note the diffuse decrease in mineral opacity of the skull and the appearance of “floating teeth.” FIGURE 27.31 Right lateral (A) and VD (B) abdominal radiographs of a dog with uremic gastropathy. The gastric wall is mineralized and conforms to the rugal folds (arrowheads). Additional imaging studies are often needed to confirm the presence of ureteral calculi, especially nonmineral opaque calculi. On excretory urography, any calculi should cause a filling defect within the contrast medium‐filled ureteral lumen. In addition, it may be possible to visualize the renal pelvis. It is important not to mistake transient ureteral peristalsis for a true filling defect. Serial radiographs should be done to help differentiate between peristalsis and a true filling defect. Ureteral dilation usually occurs secondary to obstruction. Other causes of ureteral dilation include atony and ureteritis. A mass in the urinary bladder trigone can cause dilation of both ureters. Other causes of ureteral dilation include strictures, ureteral calculi (Figure 27.33), ureteral rupture, ectopic ureters, and luminal or extraluminal masses. Inadvertent ligation of a ureter during abdominal surgery is also a consideration. Calculi, strictures, and mural mass lesions should cause a filling defect within the affected segment with proximal dilation. Smooth filling defects are consistent with calculi, strictures, and extrinsic masses. Irregular filling defects may indicate neoplasia, inflammation, or fibrosis. Pyelonephritis commonly causes proximal ureteral dilation and mild pyelectasia. FIGURE 27.32 Normal right lateral abdominal radiograph of a dog. Note the round, soft tissue to mineral opacity in the caudal retroperitoneal space, representing normal end‐on deep circumflex iliac vessels (arrowhead), commonly mistaken for ureteral calculi. FIGURE 27.33 Sagittal plane ultrasound image of a dilated right ureter with a large, round, hyperechoic shadowing, ureteral calculus. Ectopic ureter is a congenital disorder of one or both ureters where the ureteral termination is located distal to the urinary bladder trigone. Excretory urography can be very helpful in the diagnosis of ectopic ureter(s), although additional imaging studies may be needed. The most common termination sites for ectopic ureters are the urinary bladder neck and urethra, although vaginal termination can also occur. The affected ureter is often dilated and tortuous, but can appear normal, on excretory urography. The ureters are best visualized at 5, 10, and 20 minutes following contrast medium injection, and oblique VD views taken at this time are helpful in visualizing the ureteral termination site without superimposition of the vertebral spine. Moderate distension of the urinary bladder with negative contrast medium prior to administration of positive contrast medium is helpful to visualize ureteral termination. Even with these procedures, location of ureteral termination may not be possible because of superimposition of the pelvis. Ureters with abnormal termination sites close to the urinary bladder trigone are particularly difficult to diagnose, especially if the ureter is not dilated. Intramural ectopic ureters appear externally to enter the urinary bladder at the normal location, but tunnel below the mucosa and open at an abnormal caudal site. If ureteral evaluation is incomplete on excretory urography, positive‐contrast vaginography and urethrography can be performed. Computed tomography (CT) also has good success in the diagnosis of ectopic ureters and may be the imaging modality of choice for this condition [23]. Ureteroceles are cystic dilations of the intravesicular submucosal portion of the distal ureter near the termination site and may accompany ectopic ureters. They can be within the urinary bladder (i.e., intravesical or orthotopic) or in an abnormal position in association with an ectopic ureter (i.e., ectopic ureterocele) [24]. Orthotopic ureteroceles are contained entirely within the urinary bladder and have an opening in the region of the ureteral orifice. Ectopic ureteroceles have an abnormal location and may originate from the urinary bladder neck or urethral in association with an ectopic ureter. After excretory urography, the contrast medium‐filled dilation is visible within the urinary bladder (especially if prefilled with negative contrast medium) or urethra. On ultrasound, it is round, thin walled, and fluid filled, and can be located within the urinary bladder lumen (Figure 27.34). Ureteral rupture typically results in fluid accumulation in the retroperitoneal space, causing loss of serosal detail on radiographs. This is most often seen after abdominal trauma. This diagnosis is made best with contrast radiography. After contrast medium administration, the proximal aspect of the affected ureter is dilated and somewhat tortuous with contrast medium leakage at the rupture site. A ruptured ureter may be difficult to identify with ultrasound. The ureters are not seen in normal dogs and cats on ultrasound, except for intermittent visualization of urine jets when it enters the urinary bladder at the ureterovesicular junction or trigone. However, with dilation the ureter becomes apparent as a distended tubular structure with anechoic luminal fluid. The dilated ureter should be followed to try to rule out an obstructive lesion. Ureteral calculi are a common cause and are seen as hyperechoic foci with distal acoustic shadowing within a dilated, tortuous, fluid‐filled ureter. Ureteral dilation occurs in the proximal aspect initially despite the site of obstruction. Large trigonal masses usually cause bilateral ureteral obstruction. FIGURE 27.34 Transverse plane ultrasound image of the urinary bladder with a ureterocele (arrowhead) in a dog diagnosed with ectopic ureters. Proximal ureteral dilation may occur with pyelonephritis. A dilated, tortuous ureter may be visualized on ultrasound, along with retroperitoneal effusion in cases of ureteral rupture. However, the most reliable diagnosis is made with excretory urography or antegrade pyelography. Ultrasound may be used as an alternative imaging modality for diagnosis of ectopic ureters. Although not visible in every patient, the ureterovesicular junction can often be seen as a small “bump” projecting into the lumen of the caudodorsal urinary bladder wall (Figure 27.35). Urine jets can be seen intermittently at these sites, especially with Doppler ultrasonography and intravenous administration of a diuretic. The absence of a jet, and visualization of a ureter extending caudal to the urinary bladder trigone, are consistent with ectopic ureter. Ureteral dilation and ipsilateral hydronephrosis are often seen with concurrent ureteritis and stricture formation. See Chapter 20. Although radiographs and ultrasound can be obtained with a cooperative conscious patient, most contrast examinations require the patient to be heavily sedated or anesthetized. General anesthesia for these purposes allows for better patient positioning, improves patient safety, and avoids artifacts arising from muscle spasm during contrast medium administration or catheterization. FIGURE 27.35 Sagittal plane ultrasound image of a normal ureterovesicular junction in a dog. Color Doppler is used to interrogate the urine jet entering the urinary bladder from the ureterovesicular junction. In addition to the normal aspects of patient preparation for anesthesia, the descending colon and rectum should be evacuated prior to imaging. This is most appropriately achieved in dogs by administering an enema and providing the opportunity for defecation before premedication. Phosphate enemas are contraindicated in cats; instead low‐volume lubricant or warm water enemas are preferred. Survey radiographs should always be taken and assessed prior to performing a contrast study. This ensures that exposure factors are appropriate, enemas have been effective, and contrast studies are not needed if lesions are visible on survey images. Pneumocystography (negative‐contrast cystography) has some limitations and is rarely used as the sole imaging examination (Figure 27.36). The procedure is as follows. FIGURE 27.36 Pneumocystography of a dog with a large, soft tissue opaque, lobular trigonal mass.
CHAPTER 27
Urogenital Tract
Kidneys
Normal Imaging Findings
Abnormal Imaging Findings
Size
Large Kidney(s)
Small Kidney(s)
Ureters
Excretory Urography
Normal Excretory Urography
Abnormal Excretory Urography
Percutaneous Antegrade Positive‐Contrast Pyelography
Abnormalities of the Collecting System
Abnormalities of the Ureters
Urinary Bladder and Urethra
Normal Imaging Findings
Contrast Radiography
Cystography
Pneumocystography
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