Introduction

Intravenous pyelography (IVP), or intravenous urography, is a diagnostic test that involves the administration of intravenous contrast and X-ray imaging of the urinary tract. The iodinated contrast flows through the renal vasculature and filtered into the collecting system highlighting the anatomic structures on the X-ray image. It is often useful for the evaluation of hematuria, and renal stone disease, and as a follow-up after the intervention. The urographic imaging sequence is designed to depict specific parts of the urinary tract optimally. Portions of the urinary system appear opaque when filled with contrast material.[1] Accurate conclusions from the IVP are feasible only when the technique, limitations, and basic rules of interpretation are known. 

Fritz Voelcker and Alexander von Lichtenberg introduced retrograde ureteral catheterization in 1906 for visualization of the urinary tract. This technique produced variable results and was seldom successful. In 1923, Osborne and colleagues devised intravenous pyelography for visualizing the kidneys, ureters, and bladder.[2] This procedure was more practical, simpler, and safer. An intravenous method for visualizing the upper urinary tract was a substantial contribution to the field of medicine.

In modern times, ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) are commonly used for the evaluation of urinary tract diseases owing to the limitations of intravenous pyelography.[3] 

Procedures

Contrast material, radiologic table, X-ray tubes, monitor, fluoroscope, and detector are required to perform the test.

The patient must empty the bladder before the procedure. Images should systematically be obtained to improve the visualization of stones and increase the soft-tissue contrast.[4] Imaging shall include the area from the suprarenal region to below the pubic symphysis. Before the injection of contrast, the fields of calcification must undergo evaluation. Otherwise, the contrast may conceal the calcification, potentially missing the findings.

Oblique radiographs help confirm the position and nature of calcifications. This view is vital in cases where the patient may have signs of urinary tract calculus, but none is otherwise observable on the AP view.

Although unenhanced computed tomography has replaced intravenous pyelography (IVP) in the evaluation of flank pain, IVP might play a role in the follow-ups of these patients. Adjustments after contrast administration can be made based on preliminary images. The initial images play a vital role as they indicate urinary causes for the patient’s discomfort and also indirectly help detect other abdominal pathologies.

The standard procedure for pyelography consists of the following steps[1][5]:

1. A set of preliminary images (Kidney-ureter-bladder [KUB] radiograph) is necessary before contrast administration. This imaging is a crucial step and should not be missed. Additional oblique images can also be helpful. 
2. Next, a bolus of contrast should be administered.
3. After 1 to 3 minutes of contrast administration, nephrographic images should be obtained. (Oblique images are also an option.)
4. A KUB radiograph should follow five minutes after contrast administration.
5. Apply abdominal compression immediately after getting a KUB radiograph.
6. Five minutes after compression, obtain pyelographic images during early bladder filling.
7. Immediately after the release of compression, obtain a KUB radiograph and fluoroscopic spot images of ureters. 
8. Obtain the radiographic image of the bladder.

Indications

IVP is a tool in the assessment of flank and lower back pain and hematuria. It is useful in diagnosing congenital anomalies of the urinary tract, urinary calculi, enlarged prostate, neoplasms of kidney, ureter, bladder, and scars and strictures of the urinary tract.  

Imaging during early bladder filling is important in patients suspected of having a pathology of the urinary bladder. Minimal osmotic diuresis due to the use of low osmolar contrast material can cause delayed filling of the bladder. The presence of contrast can lead to excessive opacification of the bladder, which makes its assessment rather difficult. The release of compression of the abdomen allows the contrast to move into the ureters.[6][7] A KUB radiograph should be obtained just after the release of abdominal compression. This image should be supplemented with fluoroscopic spot images to view the whole luminal surface of the ureter. If fluoroscopic images are unobtainable, an oblique KUB should be ordered.[8]

In cases of obstruction, prone or oblique positions can help facilitate the flow of contrast material. In the prone position, the sacral ureter is dependent. The iodinated contrast, which is of higher specific gravity than the ureteral urine gravitates to this region and allows better visualization.[9] Delayed images in such cases should be obtained until the level of obstruction is pinpointed.

Potential Diagnosis

The results of the IVP should systematically be assessed to minimize the chances of error.

Assessment of both kidneys

1. Size 
2. Position 
3. Vertical axis 
4. Renal contour and symmetry
5. Renal parenchyma and parenchymal thickening
6. Scarring of the parenchyma
7. Calyceal distortion 
8. Cyst 
9. Double contouring of renal parenchyma
10. Rounding of forniceal margins
11. Loss of papillary impression
12. Clubbing of calyces
13. Abortive calyces
14. Aberrant papillae

Assessment of the ureters

1. Symmetry of both the ureter(s)
2. Diverticulum/diverticula of ureter(s)
3. Ureteral obstruction
4. Medial and lateral deviation of the ureter(s)
5. Obstructive and non-obstructive dilatation of ureter(s)
6. Asymmetry of the ureteral caliber

Assessment of the urinary bladder

1. Physiologic distention 
2. Position of the bladder
3. Bladder wall thickening
4. Irregularity of the lumen 
5. Contour abnormalities
6. Diverticula 
7. Neoplasms  

Normal and Critical Findings

Interpretations of the results[4]:

• The average length of the kidney ranges from 9 to 13 cms.[10]
• The average renal parenchymal thickness in the polar regions is 3 to 3.5 cms, and in the interpolar regions is 2 to 2.5 cms. 
• The upper pole of the right kidney is usually at the level of the 12th rib, and the left kidney is slightly higher than the right one. 
• The vertical axis of the kidney is parallel to the ipsilateral upper third of the psoas major.
• Parenchymal breaking and double contour may be visible in the case of a growing neoplasm. 
• Abnormal calyceal configuration can show in post-inflammatory and stone related scarring. 
• Rounding of forniceal margins can result from early and mild obstruction of the urinary tract. 
• Extensive collections of contrast material in the parenchyma can be a sign of inflammatory response. 
• Loss of papillary impression and clubbing of calyces seen in chronic obstruction. 
• Outpouchings of contrast material are evidence of the presence of diverticula.
• Aberrant papillae may be due to renal cell carcinoma. 
• The formation of phantom calyx due to a filling defect can appear in benign and malignant neoplasms.[11]
• Static columns of contrast on several images are suggestive of obstruction or ureteral ileus. 
• Separation of less than 5 cm between the ureters is considered a medial deviation. If the ureter is present more than 1cm beyond the tip of the transverse process of the vertebrae, then it is regarded as the lateral deviation of the ureter. 
• Narrowing of the ureteral lumen may be due to causes internal or external to the ureter.
• Tuberculosis of the urinary system produces remarkable signs that are visible on pyelogram, namely: moth-eaten calyces, sawtooth ureter, pipe stem ureter, and thimble bladder. The bladder appears small and contracted due to extensive mural fibrosis.[12]
• Cobra head sign on an intravenous pyelogram is visible in ureterocele.[13][14]  

Complications

Adverse reaction to the contrast material can present as hives, skin rash, and sometimes may even produce anaphylactic shock. 

Patient Safety and Education

Preparing the patient 

1. Fasting is recommended for the patient before the procedure.
2. The patient must empty their bladder before the procedure.
3. Mild laxatives may be prescribed.
4. Explain the procedure to the patient.
5. Carefully note the history of patient’s allergies, comorbidities, previous illnesses, and drug history.
6. Ask the patient to remove all jewelry and other metal objects before the procedure.
7. If the patient is a female, ensure that she is not pregnant at the time of the procedure. If she is pregnant, take precautionary measures to shelter the fetus from radiation exposure.

This examination is usually performed on an outpatient basis.

1. The patient must lie still on the table while the procedure is taking place.
2. The procedure usually takes 1 hour, but it might take longer if the kidneys are functioning at a slower rate.
3. Compression bands may be applied to properly visualize the lower segments of the urinary tract.

Clinical Significance

The clinical significance of IVP is highlighted by its extensive use in the early 20th century, to study the diseases of the urinary tract. It was a routine imaging modality of choice for the evaluation of neoplasms, ureteral obstruction, anatomical anomalies, and tuberculosis of the urinary system until the advent of ultrasonography and computer tomography, which has now largely replaced its place in renal imaging.