A renal riddle

doi:10.1136/bmj.b1424

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Thomas C Booth, specialist registrar in radiology ,
Rikin Hargunani, specialist registrar in radiology

¹Department of Radiology, Royal Free Hospital NHS Trust, London, NW3 2QG

Correspondence to: TC Booth tombooth{at}doctors.org.uk

A routine prenatal ultrasound scan found an abnormality in the fetus’s right kidney. The neonate had normal renal function, but postnatal ultrasonography of the kidney was indicated. The findings (fig 1⇓) called for further imaging tests.

Questions

1 What does the postnatal ultrasound show (fig 1⇓)?

Fig 1 Longitudinal ultrasound of kidney

2 What does the nuclear medicine scan show (fig 2⇓), and why is this an important test?

Fig 2 ^99mTc-MAG3 diuresis renogram

3 Why might this asymptomatic neonate be investigated for vesicoureteral reflux?

Answers

Short answers

1 The ultrasound image (fig 1⇑) shows hydronephrosis of the upper pole of a duplex collecting system.
2 The ^99mTc-MAG3 diuresis renogram (fig 3⇓) shows that the upper pole of the collecting system in the right duplex kidney is functioning but obstructed, as shown by the radioisotope still in the pelvicalyceal system of the right kidney at 25 minutes (red arrow) and by a flattened curve (yellow arrow). The unobstructed right lower pole with normal function is shown by radioisotope leaving the pelvicalyceal system at the same rate as in the normal left kidney. This is an important test because it shows residual function, which affects the choice of surgical intervention.

Fig 3 ^99mTc-MAG 3 diuresis renogram. Red arrow shows radioisotope is still present at 25 minutes in the upper pole of the right kidney; yellow arrow shows flattened curve of right kidney, which represents upper pole obstruction

3 Vesicoureteral reflux is a common complication of duplex kidneys, affecting the lower pole. Voiding cystourethrography is the investigation of choice.

Long answers

1 Prenatal hydronephrosis and duplex kidney

Infants referred for postnatal ultrasonography are those who, at the prenatal 18-20 weeks scan, are found to have a renal pelvic diameter of 5 mm or more.1 A prenatal renal pelvic diameter below 12 mm is usually …