Renal developmental anomalies in children

Duplex Kidneys

This is the most common anomaly (approx. 2% of the population). In the absence of complications, it is considered a normal variant.

There are two types of duplication:

• Complete: develops due to the presence of two independent ureteric buds. The topography of the orifices follows a strict rule (see the memory block). The ectopic ureter of the upper moiety may open into the vagina, causing continuous urinary leakage in girls, or form a ureterocele, which sometimes prolapses into the posterior urethra, mimicking posterior urethral valves.
• Incomplete: the ureters fuse before entering the urinary bladder. On renography, the "yo-yo" phenomenon can be observed here—pendulum-like reflux of the radiopharmaceutical between the branches of the split ureter. The mildest form of this anomaly is a septate renal pelvis.

An indirectly suspected non-functioning upper moiety in duplication on a urogram can be inferred from an increased distance to the upper edge of the nephrogram, an abnormal axis of the collecting system ("displacement" inferiorly), a smaller number of calyces, and lateral displacement of the kidney.

Crossed Fused Ectopia and Horseshoe Kidney

In crossed fused renal ectopia (Cross Fused Renal Ectopia), the kidney is located on the side opposite to the insertion of its ureter. Typically, the left kidney is displaced to the right, forming an L-shaped structure (its upper pole fuses with the lower pole of the right kidney). Ultrasound reveals a large mass of renal tissue on one side and an empty renal fossa on the other. The condition is frequently complicated by vesicoureteral reflux (VUR) and obstruction due to rotational abnormalities. It is also part of the VACTERL association (vertebral anomalies, anal atresia, cardiac defects, tracheoesophageal fistula, renal and limb defects).

Horseshoe kidney (horseshoe kidney) carries its own risks: a slightly increased probability of developing a Wilms tumour, as well as an association with genetic syndromes—trisomy 18 (Edwards syndrome) and Turner syndrome. Contrast-enhanced power Doppler ultrasound is the modality of choice for evaluating minor injuries in such a kidney.

Pelviureteric Junction Obstruction (PUJO)

Pelviureteric junction stenosis accounts for up to 40% of all cases of urinary tract dilatation. Causes may include a congenital anatomical defect, compression by an aberrant vessel, or secondary changes (scarring after infections, severe reflux).

Investigation protocol:

1. Baseline ultrasound is performed on the 7th postnatal day against the background of good hydration. An anteroposterior renal pelvis diameter of less than 7 mm is considered normal. Values of 7–10 mm require follow-up, and greater than 1 cm requires careful monitoring.
2. Renal function and urodynamics are assessed using 99mTc-MAG3 diuretic renography at an age older than 6–8 weeks (ideally after 3 months).
3. It is crucial to obtain delayed images after position changes and micturition—this is the only way to evaluate the effect of gravity on urine outflow and avoid overdiagnosing obstruction.

Surgical intervention is required in less than 25% of antenatally detected obstruction. Indications include progressive dilatation on ultrasound combined with a decline in the function of the affected kidney.

Pelvicalyceal Dilatation Scale and Complex Syndromes

To standardize ultrasound descriptions, the PCD (Pelvicalyceal Dilatation) scale is used:

• PCD 0–I: Normal (pelvis <7 mm, calyces not visible).
• PCD II: Pelvis <10 mm, calyces visible, fornices normal.
• PCD III: Pelvis >10 mm, blunted fornices, but parenchyma not thinned.
• PCD IV (and V): Marked dilatation with thinning of the renal parenchyma (down to a membrane-like rim).

In addition to isolated anomalies, complex aberrations of the anterior abdominal wall and urinary bladder occur:

• Bladder exstrophy: a defect of the anterior abdominal wall in which the bladder mucosa is everted outward. Antenatally on ultrasound, the bladder is not visualized, and pubic symphysis diastasis exceeds 25 mm. Requires staged surgery.
• Prune-Belly syndrome (Prune-Belly Syndrome): affects almost exclusively males. The classic triad includes absence/hypoplasia of the abdominal muscles (flabby, wrinkled abdomen), massive urinary tract dilatation, and bilateral cryptorchidism. Ultrasound shows a giant urinary bladder and dilated ureters with minimal intrarenal dilatation.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Differential diagnostic criteria for megaureter (primary, refluxing, non-obstructive)
• Principles for calculating differential renal function (DRF) in isotopic studies
• Radiological signs of megacalycosis and its clinical significance
• Micturting cystourethrography (MCUG): procedure protocol in children
• Neurogenic bladder: functional changes of the detrusor

Other Topics in "Pediatric Diagnostic Radiology"

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