medical information

Intravenous urography | Description | Precautions | Aftercare | Purpose | Risks

Definition

Intravenous urography is a test that x rays the urinary system using intravenous dye for diagnostic purposes.

The kidneys excrete the dye into the urine. X rays can then create pictures of every structure (kidney, renal pelvis, ureter, bladder, urethra) through which the urine passes.

The procedure has several variations and many names:

· Intravenous pyelography (IVP)

· Urography

· Excretory urography

· Pyelography

· Antegrade pyelography differentiates this procedure from "retrograde pyelography, " which injects dye into the lower end of the system, therefore flowing backward or "retrograde." Retrograde pyelography is better able to define problems in the lower parts of the system and is the only way to get x rays if the kidneys are not working well.

· Nephrotomography is somewhat different in that the x rays are taken by a moving x ray source onto a film moving in the opposite direction. By accurately coordinating the movement, all but a single plane of tissue is blurred, and that plane is seen without overlying shadows.

Every method available gives good pictures of this system, and the question becomes one of choosing among many excellent alternatives. Each condition has special requirements, while each technique has distinctive benefits and drawbacks.

· Nuclear medicine scans rely on the radiation given off by certain atoms. Chemicals containing such atoms are injected into the bloodstream. They reach the kidneys, where images are constructed by measuring the radiation emitted. The radiation is no more dangerous than standard x rays. The images require considerable training to interpret, but unique information (e.g. blood flow, kidney function, etc.) is often available using this technology. Different chemicals can concentrate the radiation in different types of tissue. This technique may require several days for the chemical to concentrate at its destination. It also requires a special detector to create the image.

· Ultrasound is a quick, safe, simple, and inexpensive way to obtain views of internal organs. Although less detailed than other methods, it may be sufficient, especially to detect obstructions.

· Retrograde pyelography is better able to define problems in the lower parts of the system and is the only way to get x rays if the kidneys are not working well. Dye is usually injected through an instrument (cystoscope) passed into the bladder through the urethra.

· A computed tomography scan (CT or CAT scanning) uses the same kind of radiation used in x rays, but it collects information by computer in such a way that three dimensional images can be constructed, eliminating interference from nearby structures. CT scanning requires a special apparatus, but often gives better information on masses within the kidney.

· Magnetic resonance imaging (MRI) uses magnetic fields and radio frequency signals, instead of ionizing radiation, to create computerized images. This form of energy is entirely safe as long as the patient does not have any implanted metal such as artificial joints, aneurysm clips, etc. The technique is far more versatile than CT scanning as it can not only demonstrate masses, but also look at the blood vessels. However, MRI requires special apparatus and, because of the powerful magnets needed, even a special, separate building. It is quite expensive and only occasionally is this degree of detail required.

Purpose

IVP will provide information concerning most diseases of the kidneys, ureters, and bladder. The procedure is comprised of two phases. First, it requires a functioning kidney to filter the dye out of the blood into the urine. The time required for the dye to appear on x rays correlates accurately with kidney function. The second phase gives detailed anatomical images of the urinary tract. Within the first few minutes the dye "lights up" the kidneys, a phase called the nephrogram. Subsequent pictures follow the dye down the ureters and into the bladder. A final film taken after urinating reveals how well the bladder empties.

IVPs are most often done to assess structural abnormalities or obstruction to urine flow. If kidney function is at issue, more films are taken sooner to catch the earliest phase of the process.

· Stones, tumors and congenital malformations account for many of the findings.

· Kidney cysts and cancers can be seen.

· Displacement of a kidney or ureter suggests a space-occupying lesion (like a cancer of the colon, rectum, or gynecological organs) pushing it out of the way.

· Bad valves where the ureters enter the bladder will often show up.

· Bladder cancers and other abnormalities are often outlined by the dye in the bladder.

· An enlarged prostate gland will show up as incomplete bladder emptying and a bump at the bottom of the bladder.

Precautions

The only serious complication of an IVP is allergy to the iodine-containing dye that is used. Such an allergy is rare, but it can be dramatic and even lethal. Emergency measures taken immediately are usually effective.

Description

IVPs are usually done in the morning. In the x ray suite, the patient undresses and lies down. There are two methods of injecting the dye. An intravenous line can be established, through which the dye is consistently fed through the body during the procedure. The other method is to give the dye all at once through a needle that is immediately withdrawn. X rays are taken until the dye has reached the bladder, an interval of half an hour or less. The patient is asked to empty the bladder before one last x ray. A compression device (a wide belt containing 2 balloons that can be inflated) may be used to keep the contrast material in the kidneys. The patient needs to urinate after the compression device is removed. Another picture is taken after the bladder is emptied to see how empty the bladder is.

In the past, of the many ways to obtain images of the urinary system, the intravenous injection of a contrast agent has been considered the best. Recent studies are showing, however, that whileintravenous urography is a useful technique, there may be other imaging techniques, such as B mode ultrasound, Doppler ultrasound, renal scintigraphy with angiotensin-converting enzyme inhibitors, intra-venous and intra-arterial catheter angiography , computed tomographic angiography, and magnetic resonance angiography, that are better or less costly.

Preparation

Emptying the bowel with laxatives or enemas prevents bowel shadows from obscuring the details of the urinary system. An empty stomach prevents the complication of vomiting, a rare effect of the contrast agent. Therefore, the night before the IVP the patient is asked to evacuate the bowels and to drink sparingly.

Preparation for infants and children depends on the age of the infant or child.

Aftercare

Feeling weak, nauseous, and/or lightheaded for a short time after the procedure is a possibility.

Risks

Allergy to the contrast agent is the only risk. Anyone with a possible iodine allergy, a previous reaction to x ray dye, or an allergy to shellfish must be particularly careful to inform the x ray personnel.

Exposure to x ray radiation should be noted. Most experts agree that the risk of exposure to low radiation is low compared to the benefits. Pregnant women and children are more sensitive to the risks of x rays.

Normal results

X-ray images of the kidney and bladder structuresappear normal.

Abnormal results

An abnormal intravenous urography result may indicate kidney disease, birth defect, tumor, kidney stone, and/or inflammation caused by infections.

Resources

BOOKS

Ballinger, Philip W., and Eugene D. Frank. Merrill's Atlas of Radiographic Positions and Radiologic Procedures. 9th ed. St. Louis, MO: Year Book Medical Publishers, 1999.

PERIODICALS

Aitchson, F., and A. Page. "Diagnostic Imaging of Renal Artery Stenosis" Journal of Human Hypertension (September 1999): 595-603.

Dalla-Palma, L. "What is Left of I.V. Urography?" European Radiology (March 2001): 931-939.

Hession, P., et al."Intravenous Urography in Urinary Tract Surveillance in Carcinoma of the Bladder." Clinical Radiology (July 1999): 465-467.

Little, M. A., et al."The Diagnostic Yield of Intravenous Urography" Nephrology Dialysis Transplantation (February 2000): 200-204.