Bladder Scan Volumes in Full-Term Newborns with Urinary Retention

Normal Bladder Physiology in Newborns

Water contributes to approximately 75% of body weight in term infants, compared to 90% in premature infants and 50% in adults 1
Newborns have smaller renal glomerular surface area available for filtration compared to older infants and adults, affecting urine production rates 1
Maximum urinary concentration capacity in term infants reaches only up to 700 mosm/l, compared to 1200 mosm/l in adults, limiting their ability to concentrate urine 1
Water turnover is high in neonates and decreases with increasing age and the concomitant decrease of metabolic rate and growth velocity 2

When performing clean intermittent catheterization in newborns, volumes less than 30 ml per catheterization for the majority of catheterizations for 3 consecutive days indicate adequate bladder emptying 1
In neonates, initial imaging should be delayed at least 48-72 hours after birth due to relatively low urine production in the immediate postnatal period 3
Exceptions requiring earlier imaging include newborns with severe bilateral hydronephrosis, bladder abnormalities, oligohydramnios, or situations where follow-up studies may be difficult to obtain 3

Renal and bladder ultrasonography (RBUS) is recommended for evaluation of febrile infants with UTIs, which may be associated with urinary retention 4
It is essential that the study be a complete renal and bladder ultrasonogram, not just a limited renal ultrasonogram 4
The patient should be well-hydrated for the examination and the bladder should be evaluated while distended 4

If volume >30 ml, consider intervention, as recommended by the American College of Radiology 1
Posterior urethral valves (PUV) are the most common cause of neonatal bladder outlet obstruction, occurring in 0.2-1% of cases of mild antenatal hydronephrosis, according to the Journal of the American College of Radiology 5
With high suspicion for PUV (bladder wall thickening, dilated posterior urethra on ultrasound), the bladder should be catheterized immediately, as per the American College of Radiology guidelines 5

Concomitant bacteremia with UTI is common in neonates and was observed in 4% to 36.4% of cases, as reported by the Journal of the American College of Radiology 6
Neonates with UTI have a high incidence of urinary anomalies; the most common is vesicoureteral reflux (VUR), according to the Journal of the American College of Radiology 6
In male newborns with UTI, voiding cystourethrography (VCUG) may detect VUR even if ultrasound is normal, as recommended by the Journal of the American College of Radiology 6

Do not delay intervention for significant urinary retention (>30 ml) as this can lead to bladder decompensation and kidney damage, as warned by the American College of Radiology 1
Do not rely solely on ultrasound to rule out vesicoureteral reflux, as it has low sensitivity for detecting VUR and renal scarring, according to the Journal of the American College of Radiology 6
Avoid unnecessary catheterization for minimal residual volumes (<30 ml) as this can increase risk of infection, as advised by the American College of Radiology 1
Do not miss posterior urethral valves in male infants with urinary retention, as this requires immediate urological intervention, as emphasized by the Journal of the American College of Radiology 5