Antenatally diagnosed renal pelvis dilatation

Editor—We were interested in the findings of Jaswon et al regarding the outcome of babies with antenatally detected renal pelvis dilatation (ARPD).1Since October 1997 it has been the practice in our unit to perform micturating cysto-urethography (MCUG) on all babies with ARPD, defined as a fetal antero-posterior renal pelvis diameter of greater than 5 mm,2 even in the presence of a normal six week postnatal ultrasound scan of the renal tract.3

Over the 16 months since this practice has been established, we identified 29 fetuses with ARPD from 3397 total deliveries (0.9%). Twenty four of 29 (83%) had ARPD of 5–10 mm, and five of 29 had ARPD of greater than 10 mm. Fifty five per cent were boys, 34% girls, and the sex was not identified in three fetuses who were lost to follow up. Postnatal follow up data were available for 18 of 29 babies. Postnatal abnormalities were detected in 13 of 18 (72%) of the babies. Six of 13 (46%) had vesico–ureteric reflux (VUR). Other diagnoses were mild unilateral pelvi-ureteric junction obstruction (n=2), posterior urethral valves (n=1), duplex kidney with obstructed upper moiety requiring heminephrectomy (n=1), bladder diverticulum without ureteric obstruction (n=1), and idiopathic hydronephrosis (n=2).

Of the six babies with VUR, four had ARPD of 5–10 mm, and two had ARPD greater than 10 mm. One baby had normal postnatal ultrasound scans (performed at 3 days, and at 6 weeks of age) with bilateral grade II VUR on MCUG. One baby with reflux had focal uptake defects on dimercaptosuccinic acid scan despite treatment with antibiotic prophylaxis from birth, and the absence of history of urinary tract infection, suggesting renal dysplasia.

To further investigate the ability of antenatal ultrasonography to detect clinically significant postnatal pathology of the renal tract, we examined retrospectively the antenatal scans of all children presenting with urinary tract infection under the age of 2 years over 12 months. Antenatal scans on these children had been performed after the introduction of our current guideline for the management of ARPD. Twenty two children (12 boys; mean age 0.5 years, range 0.06–1.16 years) presented with urinary tract infection during the study period. Fourteen babies (64%) had an underlying abnormality of the renal tract; 11 had VUR (eight isolated, one with bilateral duplex kidneys, one with bladder diverticulum). Other diagnoses were isolated bladder diverticulum (n=1), gross unilateral hydro ureter and hydronephrosis, possible vesico-ureteric junction obstruction (n=1), and idiopathic bilateral hydro ureter (n=1).

Of the 14 babies with renal tract pathology, nine had normal antenatal ultrasonography at 20 weeks' gestation, and in the remaining five data on antenatal ultrasonography were missing.

In conclusion, our data support the proposal by Jaswonet al that all babies with ARPD of greater than 5 mm should be investigated by MCUG regardless of a normal postnatal ultrasound scan of the renal tract. Even with this strategy, however, our results suggest that not all cases of clinically significant postnatal renal pathology are identified, and a significant proportion of infants and toddlers presenting with urinary tract infection have underlying renal tract pathology despite normal antenatal ultrasonography.