Catheters and X-rays

Our practice sees many children below the age of 3 months for urological conditions, either picked up in utero or in neonates who have been treated for a urinary tract infection.

The studies which usually generate some debate from parents are those studies requiring catheterization of the bladder, such as the cystourethrograms (either the contrast study or the isotope form) and the MAG 3 Lasix renal scan used to objectively determine the likelihood of an obstruction to kidney drainage. A catheter is used in this study to prevent a full bladder from possibly affecting ureteral drainage.

1. Voiding Cystourethrogram

Although the nuclear cystogram averages about 12% of the radiation dose of a fluoroscopic voiding cystourethrogram (VCUG), we prefer the contrast VCUG in both males and females, at least as an initial study, in order to get an idea of bony and in particular lumbosacral vertebral anatomy. In addition, viewing urethral anatomy is especially important in boys.

We normally wait to perform the VCUG until the urine is clear of infection so that bladder filling pressures are not compromised by bladder wall inflammation.

Aseptic catheterization is usually performed on the fluoroscopy table and a urine sample sent for culture. The catheterization is usually done without sedation so as not to have the voiding phase compromised by sedation.

The catheter, usually a feeding tube in infants, is inserted after 1% Xylocaine jelly is instilled in the urethra. The catheter can be taped to the thigh to prevent a bladder spasm extruding it. A KUB is then performed to check bony anatomy immediately prior to performing the filling phase of VCUG. Early filling allows a check for filling defects from ureteroceles, and oblique views can document low-grade vesicoureteral reflux (reflux) during filling. AP views can then allow comment on the degree and grade of reflux. When the bladder is full, the infant will usually initiate spontaneous voiding, and fluoroscopic views are taken during this voiding phase of the VCUG. Oblique views during this phase offer anatomic detail of the male urethra. As soon as the voiding phase is initiated, we remove the catheter for more complete voiding views of the urethra. (Some radiologists debate this issue!)

2. Diuresis Renography

Diuresis renography, also known as the MAG 3 Lasix renal scan, is used to attempt to determine whether a dilated ureter is obstructed or not. These obstructions occur usually at the ureteropelvic junction (UPJ) and less commonly at the ureterovesical junction (UVJ).

Rarely, a dilated ureter may be refluxing and obstructed. Routinely, after a feeding tube catheter has been placed into the bladder, a weight-adjusted dose of isotope and 1 mg/kg of furosemide (Lasix) is administered intravenously at the same time. Posterior imaging of the kidneys and bladder is then performed for 20 minutes followed by gravity-assisted drainage or imaging after voiding. Routinely, a NORMAL NON-DILATED URETER will have a Lasix clearance half-time of less than 10 minutes.