Ultrasound

• First-line imaging modality for most suspected anomalies of the urinary tract
• Compare the patient’s renal length with tables of normal renal length vs age
• Left and right kidneys should normally be within 1 cm of each other in length.
  • Discrepancy due to too small kidneys:
    • Global scarring
  • Discrepancy due to too large kidney:
    • Acute pyelonephritis
    • Renal duplication

Different characteristics of infants kidneys compare to older children and adults includes:

• Undulating contour secondary to persistent fetal lobulation (columns of Bertin)
• More echogenic (can be iso or hyperechoic to adjacent liver parenchyma)
• Thinner renal cortex
• Prominent renal pyramids and hypoechogenicity compare to the renal cortex → can be mistaken for cysts or dilation of the collecting system.

Voiding Cystourethrogram (VCUG)

Strength

• Can demonstrate presence or absence of vesicoureteral reflux (VUR)
• Demonstrate anatomic abnormalities of the bladder and urethra

Indication includes:

• Evaluation of urinary tract infection (UTI)
• Voiding dysfunction
• Enuresis
• Work-up for hydronephrosis

Procedure

• 8F urinary catheterization
• Precontrast scout view of the abdomen
  • Evaluate calcifications
  • Bowel wall pattern
  • Confirm catheter position within the bladder
• Bladder contrast filling via catheter
  • Early filling view to exclude a ureterocele
  • Full contrast bladder: bilateral oblique views to visualized ureterovesical junctions (UVJ)
• Voiding
  • Include urethra in imaging (especially for male)
  • Can be obtained with the catheter in the urethra (does not prevent the diagnosis of posterior urethral valves)
• Complete void
  • Imaging of VUR and postvoid residual contrast within bladder and renal collecting systems

Dose reduction techniques

• Use “last-image hold images” instead of true exposures
• Brief and intermittent fluoroscopy during bladder filling

Expected bladder capacity

The amount of contrast needed to fill a child’s bladder can be calculated using the following formula:

Expected bladder capacity (in mL) = (age (in year) + 2)x 30

Nuclear Medicine

^99mTc-DMSA

Can be used to evaluate

• Relative renal function (right vs left)
• Renal cortical defects
  • Infection
  • Infarction
  • Scarring

^99mTc-MAG3

• Primary active tubular excretion
• Used in suspected urinary tract obstruction (with a furosemide challenge)

Magnetic Resonance Urography (MRU)

Increasingly utilized, yet constrained by its cost, availability, and the requirement for sedation.