The anatomy of a duplex kidney and the site of insertion of its ureters are sometimes difficult to demonstrate preoperatively, particularly if the kidney moiety is poorly functioning. Magnetic resonance urography (MRU) has been found to be superior to conventional imaging techniques in delineating poorly functioning moieties of duplex kidneys and ureteral ectopia.[^{1, 2}]

A 6-year-old girl was brought with history of dribbling of urine in between normal acts of micturition from early in life. The child was otherwise well and abdominal examination did not reveal any abnormality. Urine was dribbling in small amounts from the vulva. The urethral and vaginal orifices were normal on inspection. Urine examination, urine culture and blood parameters for renal function did not reveal any abnormality. Ultrasonogram (USG) of the renal tract showed left duplex with hydronephrosis of the upper moiety of the kidney and a normal lower moiety. The dilated and tortuous upper moiety ureter was seen behind the bladder with narrowing of its distal end [Figure 1].

Intravenous urogram (IVU) also showed the duplex kidney on the left side. The lower moiety of the left kidney, its ureter and the whole of the right renal system appeared normal. The upper moiety of the left kidney was hydronephrotic and the proximal ureter of the upper moiety was seen mildly dilated near the renal hilum. The rest of the upper moiety ureter could not be demonstrated on IVU [Figure 2]. The degree of dilatation of the proximal ureter of the upper moiety as seen in IVU did not correspond to the massively dilated distal end of the lower ureter seen on USG.

MRU was performed using intravenous DTPA-Gadolinium contrast to delineate the anatomy of the left duplex better. MRU showed the dilated upper moiety of the left duplex. The lower pole ureter on the left side was of normal caliber and entered the urinary bladder [Figure 3]. The upper moiety ureter on the left side was dilated and tortuous was seen in its entire length. Its distal end was narrow and after coursing behind the bladder opened below the bladder neck [Figures 4–6]. The right kidney and its ureter were normal. Upper pole nephroureterectomy was done with excision of the upper ureter to just above its terminal end.

Magnetic resonance urography (MRU) has the advantage that in a single study, three-dimensional imaging of the entire urinary tract as well as assessment of renal function and urinary drainage can be done. It does not employ ionizing radiation and can be used in the presence of iodine-based contrast allergy or impaired renal function.[^{1, 2}] Static fluid T2 weighted images in MRU are particularly useful to show large fluid-filled structures as in pelviureteric junction obstruction, cystic renal disease, complicated duplex renal anomalies including nonfunctioning moieties, large ureteroceles, and dilated ectopic ureters.[^{3, 4}] Static fluid MRU does not require any contrast. Contrast-enhanced T1 images of (excretory) MRU delineate subtle anomalies such as nondilated duplex kidneys, small bladder diverticulae and ureterocoeles.[³–⁵] Very clear images of the urinary tract can be obtained by maximum intensity projection (MIP) on heavily T2 weighted images. MRU has about 99% sensitivity and greater than 90% specificity for the diagnosis of duplex renal system.[³] In the presence of poorly functioning renal moieties, MRU is more successful than IVU and computerized tomographic urography (CTU) in demonstrating the anatomy of complicated duplex anomalies.[³–⁶]

Among the congenital urinary anomalies ectopic ureters often pose diagnostic and therapeutic challenges.[⁷] Demonstration of the anatomy of the ectopic ureter such as its course, relation to adjacent structures and site of insertion is sometimes difficult with conventional imaging and endoscopy.[^{1, 7}] Single system ectopic ureter has been reported to be more common than ectopic ureters associated with duplex kidneys in India but requires further confirmation.[¹] MRU is currently considered ideal for assessment of ectopic ureters, complicated duplex systems or when other complex abnormal anatomy of the urinary tract is suspected.[^{2, 5}]

In our patient, cystourethroscopy and genitoscopy did not show the ectopic insertion of the left upper pole ureter, possibly because of the stenosis of its distal end. MRU clearly demonstrated the anatomy of the left duplex, particularly the entire extent of the dilated upper moiety ureter, its narrowed distal end and termination below the bladder.

With increasing availability of MRU in many centers, it may become the preferred imaging modality after an USG in duplex renal anomalies and ureteral ectopia.[⁴–⁶] MRU may also be used to clarify any discordant results of conventional imaging techniques.

Source of Support: Nil

Conflict of Interest: None declared.