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Prenatally Diagnosed Urinary Tract Anomalies

Jeeta Dhillon
London, England

 

Correspondence:

Jeeta Dhillon
Perinatal Urologist; Great Ormond Street Hospital for children, Greater London WC1N3JH,

London, Engand.

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Routine maternal ultrasound was introduced in the late 70’s and within the decade was established as a safe and useful Obstetric tool. In the United Kingdom all pregnancies now have a detailed anomaly scan at about 20 weeks of gestation. Further scans are indicated if an abnormality is detected. Abnormalities of the renal tract are also diagnosed later on in gestation if there is an Obstetric complication which warrants further scans.The urinary tract is easily visualised and urological abnormalities are detected in approximately 1 in 500 pregnancies. 

The diagnosis of a renal tract abnormality during the pregnancy generates considerable anxiety for the parents and this is proportionate to the number of scans carried out both pre and postnatally. The vast majority of these children do not have a life threatening abnormality and greater emphasis needs to be placed on improving prenatal counselling so that the parents are appropriately informed about the prognosis of the abnormality. Improved counselling for the families can only be achieved by close collaboration between the Obstetric or Fetal medicine units and postnatal specialists. This is mandatory if the fetus is found to have life threatening abnormalities or where there is a significant risk of serious renal impairment. This population of children with a prenatally diagnosed renal tract abnormality is unique. The vast majority are perfectly healthy and asymptomatic. They are therefore not patients in the traditional sense. This simple fact is often overlooked and these perfectly healthy children are often subjected to excessive invasive investigations and even unnecessary surgery.

Although a considerable amount of information is currently available about optimal Paediatric management, there are still no long term outcomes beyond 15 years. New centres in particular should manage all prenatally diagnosed uropathies according to protocol with detailed documentation of the findings and outcomes. The aim of Perinatal urology units is to elucidate the natural history of each diagnostic group so that the population at risk of renal functional deterioration and symptoms can be prospectively identified. Prenatal ultrasound has also identified children with a minor abnormality that poses no risk to their well being. This ‘benign’ population currently requires minimal imaging and may not even require any postnatal follow up within the decade as more information becomes available. The concept of a ‘benign’ population is very well illustrated by the multicystic kidney which was classically diagnosed because of a palpable abdominal mass. In our unit, 75% of prenatally diagnosed multicystic kidneys were not palpable within the first 3 months. Therefore the majority of this new population of prenatally diagnosed multicystic kidneys would have escaped detection 20 years ago. The natural history of these kidneys is one of involution and by 5 years of age almost 50% of these kidneys are not detectable on ultrasound.

Optimal management of urinary tract abnormalities is both prenatal and postnatal. Ideally postnatal specialists should be involved in prenatal counselling which requires considerable expertise as the vast majority of renal tract abnormalities are non specific and are a differential diagnosis. However, even in the absence of joint counselling, optimal postnatal management demands a detailed prenatal history. The baby should not be subject to any investigations until there is clear documentation of the timing of the abnormality, the progression and the exact measurements of the dilatation/abnormality. The two main problems arising from the advent of routine maternal ultrasound are the diagnosis of a pelviureteric junction “obstruction” (PUJO) and the management of “mild hydronephrosis” The first group comprises children with an isolated upper tract dilatation and constitutes 50% of all prenatally diagnosed uropathies. In our unit, this population was first managed conservatively in a natural history study. This was then followed by a randomised clinical trial and the information from these and subsequent studies has helped to define the population with a true PUJO from children with an insignificant renal pelvic dilatation.

Our studies over the last 25 years have demonstrated that ultrasound is the most useful imaging modality in terms of dividing children with a potential PUJO into those who require pyeloplasty from those who have a hydronephrosis of no clinical significance. Only 11% of children with a pre and post natal dilatation of <20mm have required surgery. The children requiring pyeloplasty were found to have an intra renal kind of hydronephrosis where the renal pelvis was not severely dilated but the calyces were equally or even more dilated than the pelvis. Such intra renal hydronephroses benefit from pyeloplasty within the first 6 months even if the radioisotope study affords the kidney good function.

On the other hand, more than 95% of children with a hydronephrosis of >30mm with calyceal involvement and initial good function will eventually require surgery. This population should not be managed conservatively and benefit from a pyeloplasty in the first 6 months of life.

The only group of children with a severe hydronephrosis who do not require a prophylactic pyeloplasty are those with a dilatation of between 2030mm and calyceal involvement. Although 40% of this group have required surgery, a similar number have improved spontaneously. These children should therefore be managed conservatively and only warrant surgery if the function decreases, the dilatation increases or if they have symptoms related to their hydronephrotic kidney. The difficulty in the management of prenatally diagnosed “mild hydronephrosis” arises from its apparent association with severe reflux.

This has led to the unjustified and widespread use of routine micturating cystourethrography (MCUG) without rational. In fact this relationship between mild dilatation and severe reflux is only true if the prenatal scans are ignored. Children with severe reflux will prenatally either have bilateral hydronephroses, dilated ureter(s), distended bladder, abnormally echogenic or small kidneys. Some of these prenatal abnormalities may not be visualised postnatally especially if the baby is dehydrated or if the bladder is empty. Hence the indications for an MCUG should be based on the prenatal findings which will identify children who may have severe reflux with a mild postnatal dilatation. Prenatal ultrasound has identified a large population of perfectly healthy children with a wide spectrum of urinary tract abnormalities.

The majority of children with a radiological diagnosis of multicystic kidney, reflux, pelvi ureteric or vesico ureteric junction “obstruction” are a new population with very little historical clinical significance. Prenatal ultrasound can prevent children from suffering functional deterioration or urinary tract infections. However, this must be achieved without the majority having inappropriate imaging and unnecessary surgery.