Which of the following procedures requires that contrast medium be injected into the ureters A?

EXCRETORY UROGRAPHY

Excretory urography (intravenous pyelography) relies on the administration of intravenous contrast to enhance the urinary tract and thereby have it stand out against the remainder of the abdominal tissues.111–114 As other modalities have been applied to the study of urinary tract disorders, use of excretory urography has fallen off sharply. Ultrasound, CT, MRI, and nuclear medicine have to a degree replaced excretory urography.115–118 At this point, if used at all, excretory urography is performed to delineate and characterize the anatomy of the urinary tract. Congenital variants in ureteral anatomy including ectopic ureters and collecting system duplication can be delineated in this manner. For instance, urinary dribbling in girls remains in many institutions and for many urologists an indication for excretory urography in assessing for variant insertion of the ureter.119,120 Diseases of the urothelium and papillary necrosis can also be accurately diagnosed and followed with excretory urography.121

Certainly if excretory urography is performed, care must be taken with respect to administration of intravenous contrast. Issues of nephrotoxicity and allergy to intravenous contrast must be considered. To minimize radiation dose, the number of radiographs obtained as part of the study should be kept to a minimum but without sacrificing the diagnostic performance of the test.

Intravenous Urography

Intravenous urography (IVU; also known as intravenous pyelography, or IVP) provides both functional and anatomic data, particularly of the ureter. Until recently, it was considered to be the gold standard for imaging in acute renal colic. However, the procedure has significant drawbacks including contrast nephrotoxicity and the fact that it is contraindicated in pregnancy. Furthermore, kidneys may not be visualized in cases of severe obstruction as the suppressed glomerular filtration rate (GFR) may not allow excretion of the contrast material. All these concerns have led to replacement of IVU with computed tomography (CT), ultrasound (US), and magnetic resonance imaging (MRI) in many cases.

18 Because CT detects all stones, when is IVU necessary in patients with urinary tract stones?

IVU is helpful in showing the anatomy of the urinary tract in patients with recurrent stones, in patients in whom stone passage is arrested in the ureter, and in patients in whom surgical intervention is being considered to treat the stones. In such cases, IVU helps identify congenital or acquired abnormalities that may be potentiating stone formation, collecting system damage related to chronic stone disease, and ureteral strictures that may prevent spontaneous passage of stones. Stones that are smaller than 5 to 6 mm almost always pass spontaneously, whereas larger stones may require surgical intervention.

IVU may also show abnormalities, such as medullary nephrocalcinosis, that may be contributing to recurrent stone disease. Clustered calcifications are present in the medullary pyramids in patients with medullary nephrocalcinosis, which can be due to medullary sponge kidney, renal tubular acidosis, or hyperparathyroidism—the latter two diagnoses are made on clinical grounds, but medullary sponge kidney, in which the collecting ducts are dilated and prone to form stones, can be diagnosed only by IVU.

Intravenous Urography

IVU has been all but replaced in pediatric imaging by other modalities, including US, renal scintigraphy, computed tomography (CT), and magnetic resonance urography, with few indications for the examination remaining. In fact, because of the widespread availability of CT, few pediatric radiology departments in the United States have even retained the ability to perform linear tomography. As a result, even if IVU is to be done, its performance is usually limited to a series of plain radiographs alone. In our own department, we perform at most two to three IVUs a year, in each case at the insistence of the referring physician and despite our own recommendation that another modality be performed in its place. Nonetheless, images simulating those obtained with the conventional IVU are at times obtained after administration of intravenous iodinated contrast media for other examinations (e.g., computed tomography, abdominal or cardiac angiography). Although the diagnostic value of such images may be more limited than with formal IVU, the principles of interpretation are the same.42

The minimum approach to the pediatric IVU includes a scout view of the abdomen and pelvis before contrast material is administered and two anteroposterior radiographs of the abdomen and pelvis at 5 and 10 minutes. Additional oblique or lateral views and delayed images can be obtained as required. Serious allergic and other adverse reactions to intravenous contrast media are relatively rare in children, particularly when non-ionic, low-osmolarity urographic contrast media are used.43 Appropriate preparation of the patient for the examination by fasting is important, both to improve visualization of contrast material in the kidneys and ureters and to reduce the frequency and severity of contrast-induced nausea and vomiting.

Excretory Urography

Excretory urography is waning as a diagnostic modality in the evaluation of pediatric uropathy. Even with tomography, the information gained is limited. Stool, bowel gas, and immaturity of the neonatal kidney limit its utility. In addition, the degree of hydronephrosis noted does not equate to severity of obstruction. Rarely, excretory uropathy may have a helpful role when further anatomic definition is required.45 When anatomic detail is required, furosemide (1 mg/kg) given 3 minutes before contrast material enhances the multislice CT scan and shows promise at defining the pathologic defect better than intravenous urography and ultrasonography.46

Intravenous urography

Historically, intravenous urography (IVU) was the radiographic modality of choice for noninvasive assessment of the urinary tract. As an imaging study, it combines anatomic accuracy with qualitative information regarding renal function and obstruction. IVU is now infrequently used in the assessment of a pediatric patient with obstructive uropathy and has been replaced by sonography and scintigraphy. Obstruction, on IVU, of the kidney may be inferred from delay in the appearance of contrast material or a negative nephrogram, a delay in drainage, dilution of contrast medium, or uniform cortical loss.

Diagnosis

The diagnostic workup relies on the use of ultrasound, MCUG, and renal isotope scans.

Excretory urography, the mainstay of ureterocele diagnosis until a decade ago, is much less commonly used now. Computed tomography scan and magnetic resonance urography may be useful, especially the latter, when the urinary tract anatomy is not clear.

Ultrasound of the urinary tract is the first investigation and generally depicts clearly the ureterocele as a sonolucent round image that sits on the bladder base and occupies a portion of the bladder. One or more dilated ureters can be seen behind the bladder (Fig. 115-5). Ultrasound gives valuable information on the presence of unilateral or bilateral renal duplicity and on the dilatation of the collecting systems, and it helps in identifying which kidney is drained by the ureterocele. Cortical cysts and severe parenchymal thinning, but not increased echogenicity, suggest renal dysplasia that is confirmed by isotope scan.71

An MCUG is an essential part of a ureterocele evaluation. The ureterocele is seen in the first films as a negative shadow in the bladder, with a rim of contrast around it. If the ureterocele is not tense, it may be obscured with the progressive filling of the bladder because it may be compressed or, if it is small, may be obscured by the contrast medium around it. MCUG may also reveal VUR in the lower pole ureter (50%) or in the contralateral ureter (25%).53,72,73 In less than 10% of cases, reflux can be identified in the ureterocele if it is ruptured or if it has a large open meatus placed on the bladder neck that allows reflux during voiding.33,73 The MCUG is also useful to ascertain the degree of the detrusor backing for the ureterocele. If the detrusor support is poor, the ureterocele may evert during micturition, mimicking a bladder diverticulum (Fig. 115-6). During voiding, the ureterocele may also be seen prolapsing through the urethra and obstructing the urinary flow.

IVU was the most important diagnostic step in the past. More recently, however, the progress of ultrasonography, DMSA, and MRI has made this examination obsolete in most cases. Nevertheless, when the anatomy is confusing, excretory urography may still play a role.

If the renal parenchyma associated with the ureterocele retains some function, which most commonly occurs in single systems, a characteristic “cobra head” or “spring onion” deformity of the intravesical ureter is produced due to opacified urine in the ureterocele being surrounded by a radiolucent halo that represents the wall of the ureter. More commonly, when the ureterocele is associated with the upper pole of a duplex kidney, function is absent or minimal in 90% of cases; therefore the radiographic signs are mainly negative, reflecting the displacement of the lower pole renal unit by the hydronephrotic upper pole ureter. The lower pole pelvis is often laterally and downward displaced, producing the characteristic “drooping lily” appearance; the number of calices is reduced; and the upper calices are missing (Fig. 115-7).

At the bladder level a negative shadow may be seen, suggesting the presence of a ureterocele (see Fig. 115-7). The shadow may vary from a large, tense, round shadow occupying most of the bladder to a minor irregularity in the base of the bladder.

Excretory urogram also shows the condition of the contralateral kidney collecting system that may be duplex (see Fig. 115-7) or may be obstructed at the bladder level by a large and tense ureterocele compressing the ureteral orifice.

The function of the pole or of the kidney associated with the ureterocele is best assessed by a DMSA renal scan that shows the quality and quantifies the amount of functioning renal tissue (Fig. 115-8).

Intravenous Urography

The intravenous urogram (IVU) is also known as the intravenous pyelogram (IVP). A scout or plain film (KUB) is performed initially. Subsequently, iodinated contrast material is injected intravenously, ideally via bolus injection. Timed, sequential images of the kidneys and remainder of the genitourinary system are then obtained. The first film, taken within 30 to 60 seconds, demonstrates a nephrogram, which may be used to evaluate the size, shape, and contour of the kidneys. The anatomic depiction of the calyces, infundibula, and pelvis is best displayed within 5 to 10 minutes. Imaging of the ureters is usually accomplished at 10 to 15 minutes, and the drainage of the contrast material from the kidney and ureters allows for a global assessment of the urinary bladder.

Intravenous Urography and Pyelography

The traditional intravenous urogram (IVU), which is used to evaluate the kidneys, kidney function, and ureteral excretion and function, has undergone a radical transformation over the past 10 years, with increasing resolution and performance of CT, magnetic resonance imaging (MRI), and ultrasound (see Figs. 8-2 and 8-3). Evaluation of the kidneys is best performed with contrast-enhanced CT or MRI (Figs. 8-4 and 8-5). Evaluation of the ureters also may be performed with CT or MRI, although a fluoroscopic or radiographic examination, if performed properly, may be adequate, especially when detecting urothelial malignancies. Advances in competing technologies have limited or severely restricted the clinical application of the IVU. The intravenous urogram is no longer indicated for many upper tract indications, such as renal mass evaluation and evaluation of acute renal colic, and is best reserved for evaluation of hollow parts of the urinary system, such as follow-up of patients with transitional cell carcinoma.1

Other Radiologic Studies

Historically, the IVU with renal tomograms was used to identify renal scarring, but in most situations DMSA scintigraphy has assumed the role of the IVU. Of course, IVU still identifies collecting system abnormalities with more detail than either DMSA or ultrasonography. Currently, IVU does not play a role in the initial evaluation of a UTI, but it may be useful in patients with bacterial persistence.

No extensive studies have directly compared the sensitivity and specificity of DMSA and CT or MRI for detecting renal lesions in acute or chronic pyelonephritis. However, in one study comparing the use of MRI and nuclear imaging techniques in a cohort of 37 children with acute pyelonephritis, MRI was found to detect more acute pyelonephritic lesions with superior interobserver reliability when compared to DMSA scans.227,228 However, for routine acute UTI evaluation, neither modality is practical. In children with complicated infections, either CT or MRI may be useful for defining renal abnormalities and extent of disease and either is probably as sensitive as DMSA for detecting renal scars.229,230 Recent MRI protocols provide excellent definition of the renal cortex and collecting system and accurate assessments of function.231