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Paediatric Genitourinary Disorders
Duplex Kidney
Duplex Kidney
Definition
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A congenital abnormality where drainage of the kidney is via two collecting systems (occurring in 3% of individuals)
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Partial < complete
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Bilateral > unilateral
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Complete duplication
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The ureters draining the two moieties never join
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Classically the upper moiety ureter obstructs (its ectopic ureteral orifice is often stenotic) and the lower moiety ureter tends to demonstrate vesicoureteric reflux (due to an incompetent valve)
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The upper moiety ureter usually enters the bladder as a ureterocele ▸ such ectopic drainage is almost always associated with dysplastic function of the upper moiety of the kidney
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Weigert–Meyer rule: the upper moiety ureter inserts into the bladder inferomedial to the lower moiety ureter
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Other ectopic insertions of the upper ureteric moiety: bladder neck ▸ posterior urethra ▸ seminal vesicle or ejaculatory duct ▸ vagina
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Incomplete duplication
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The two ureters join at any level above the bladder
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‘Yo-yo’ reflux: this may occur if urine refluxes from one ureteric moiety into the other (rather than draining into the bladder) if there is ureteric duplication above the bladder – a septated renal pelvis is the mildest variant of this condition
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Clinical Presentation
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Asymptomatic ▸ the development of a UTI
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Pain: secondary to intermittent obstruction at the PUJ level of the lower moiety or due to ‘yo–yo’ reflux with incomplete duplication
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Continuous wetting in a girl: due to an ectopic insertion of the upper moiety into the vagina
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Vaginal prolapse: the ureterocele prolapses out of the bladder
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Bladder neck obstruction: following prolapse of a ureterocele
Radiological Features
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One of the cardinal signs of a duplex system is a change in the axis of the lower moiety
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The lower moiety calyces are medial to the upper moiety calyces (giving the lower moiety of the kidney a longitudinal axis which points to the ipsilateral shoulder)
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US
A duplex kidney is longer than normal in bipolar length (for an uncomplicated duplex) ▸ the kidney may simply show two distinct renal pelves
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Upper moiety: this is usually dilated ▸ this may be normal, small, or dysplastic ▸ it may be anechoic and resemble a ‘cyst’ (which is an obstructed ureterocele) ▸ these findings are generally associated with a dilated ureter
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Lower moiety: in complete duplication the lower moiety may be normal and difficult to recognize ▸ the calyces and pelvis of a lower moiety may be dilated with no ureteric dilatation (suggesting a PUJ stenosis) ▸ reflux is likely when a dilated ureter is seen
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Ureterocele: this is seen at the bladder base if it is intravesical ▸ it can be so large as to be mistaken for a bladder
IVU
‘Drooping lily’ sign: an obstructed upper pole moiety will not opacify – the opacifying lower pole moiety will be displaced inferiorly by the mass effect from the obstructed and enlarged upper pole moiety
99m Tc-MAG3
This will assess the function, drainage, and the presence of any reflux (especially with late images) ▸ if a moiety is non-functional it will not be visualized (this is important to recognise when there is a small severely dysplastic upper moiety) ▸ with incomplete duplication the upper and lower moieties may be normal or there may be reduced function of either element
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‘Yo-yo’ reflux is seen with an incomplete duplication
Micturating cystourethrography
A ureterocele appears as a filling defect along the posterolateral wall of the bladder on early images (this will be obliterated once the bladder is full of contrast medium)
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VUR may be detected (usually into the lower moiety) ▸ reflux into the upper moiety is rarely detected
Pearls
Ureterocele
A submucosal dilatation of the intramural distal ureter, which often projects into the bladder lumen ▸ it is usually associated with the upper moiety ureter of a duplex system (and may obstruct the ipsilateral lower moiety ureter)
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It may also prolapse into the urethra (causing bladder outlet obstruction) or present as a labial and interlabial mass
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Ureteroceles that are not associated with a duplex system tend to be small and are not associated with significant obstruction (unless complicated by calculi)
IVU
A ‘cobra's head’ appearance: a contrast-filled structure (the ureterocele cavity) with a thin radiolucent wall (the ureterocele wall) surrounded by contrast within the bladder
US
A thin-walled cystic structure projecting into the bladder lumen
Congenital Renal Anomalies
Abnormalities of Fusion
Horseshoe Kidney
Definition
A common renal anomaly (affecting 1:400 live births and M > F) whereby in utero contact between the metanephric tissue of the developing kidneys results in a midline connection (isthmus) between the lower poles ▸ the isthmus may be anything from a fibrous band, to more commonly a block of renal tissue
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The ascent of the fused kidney is arrested by the inferior mesenteric artery during development, resulting in a low abdominal position (the isthmus lies anterior to the aorta and IVC but posterior to the inferior mesenteric artery) ▸ its abnormal position makes it more susceptible to injury
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It is always associated with malrotation so that the pelves and ureters pass anteriorly over the fused lower poles
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Associations: PUJ obstruction (30%) ▸ duplicated ureter (10%) ▸ medullary sponge kidney ▸ anorectal and musculoskeletal anomalies
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Complications: renal pelvic dilatation (± PUJ obstruction) ▸ renal calculi or infection ▸ there is an increased risk of renal tumours (e.g. a Wilms' tumour) ▸ may be associated with trisomy 18 (Edwards' syndrome) and Turner's syndrome
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US
This may not detect the abnormal axes of the kidney
99m Tc-DMSA
An anterior view is useful to show all functioning renal tissue (especially over the spine)
CT/MRI
These can easily demonstrate a horseshoe kidney (the upper poles point superolaterally, the lower poles inferomedially)
Pancake kidney
A rare fusion anomaly whereby both kidneys have failed to ascend from the pelvis and have fused
Cross-Fused Renal Ectopia
Definition
One kidney is displaced across the midline and is fused inferiorly to the other relatively normally positioned kidney (both ureters enter the bladder in a normal position) ▸ there is an increased incidence of VUR into the crossed kidney
Clinical presentation
It may present as an abdominal mass or as an obstructive uropathy with a PUJ obstruction ▸ it is more common on the right (M>F) – the left kidney is more commonly the ectopic kidney
US
An unusually large kidney on the affected side and an absent kidney on the opposite side
99m Tc-MAG3 study
This is performed if surgery is being considered for a PUJ obstruction
99m Tc-DMSA scintigram
Patchy uptake of the isotope owing to the anatomical abnormality and dysplasia that exists to some degree
MCUG
This may provide further anatomical information
Pancake Kidney
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Occurs when bilateral pelvic kidneys fuse
Abnormalities of Position
Malrotated Kidney
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The upper pole of the kidney is located more laterally than the lower pole (the upper pole calyces are therefore lateral to the lower pole calyces) ▸ a malrotated kidney may develop urological complications, be more susceptible to trauma, or indicate that pathology in an adjacent organ is displacing the kidney
Ectopic Kidney
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Failure of complete ascent: this results in a pelvic kidney (the majority) ▸ there is an increased risk of trauma, VUR and calculus formation (due to urinary stasis)
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Overascent: this is almost always limited by the diaphragm but if there is eventration of the diaphragm or a Bochdalek hernia an intrathoracic kidney may result ▸ this can resemble a posterior mediastinal mass
Congenital Renal Anomalies
Unilateral Renal Agenesis
Definition
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This follows failure of the ureteric bud to reach the metanephros (affecting 1 in 1250 live births) ▸ the ipsilateral ureter and hemitrigone fail to develop but occasionally a ureteric stump may remain ▸ as an antenatal diagnosis is uncommon this suggests that agenesis may represent an involuted multicystic kidney ▸ bilateral renal agenesis is incompatible with life
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It can be difficult to differentiate between unilateral agenesis and a small non-functioning kidney (especially if it is ectopically located)
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Associations
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Ipsilateral urogenital abnormalities are common (absence of the vas deferens or absence of the seminal vesicle) ▸ cardiovascular, gastrointestinal and musculoskeletal anomalies ▸ the VATER syndrome
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Females with renal agenesis have a 70% incidence of Müllerian anomalies (vaginal/uterine agenesis, or unicornuate uterus which are part of Mayer–Rokitansky–Küster–Hauser syndrome)
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Bilateral renal agenesis results in Potter's syndrome consisting of oligohydramnios, pulmonary hypoplasia and facial abnormalities (low set ears/broad flat nose/prominent infraorbital skin folds)
Radiological Features
US/CT/MRI
There is compensatory hypertrophy of the normal contralateral kidney
99m Tc-DMSA
This can exclude a small ectopic kidney
Tuberous Sclerosis
Definition
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An autosomal dominant condition characterized by multiple hamartomas in the brain, skin, kidneys, liver, lungs and heart (e.g. a cardiac rhabdomyosarcoma)
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Renal manifestations: this is most commonly an angiomyolipoma (AML) ▸ renal cysts or a renal carcinoma can also be present
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If renal cysts are found in a child < 5 years with no family history, tuberous sclerosis must be excluded
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Radiological Features
US
Multiple cysts (similar to ADPKD) ▸ during later childhood there may be multiple small rounded echogenic foci throughout the renal parenchyma representing multiple AMLs (with an increased risk of haemorrhage if an AML is > 4 cm)
CT
Multiple fat-containing renal masses
Supernumerary Kidneys
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This is extremely rare ▸ it is usually left sided, hypoplastic and caudally positioned
Septum of Bertin
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This represents a prominent column of Bertin (cortical tissue that separates the pyramids) ▸ it is usually located at the junction of the upper and middle ⅓ of the kidney ▸ it may be mistaken for a renal mass and is associated with a bifid renal pelvis consisting of two pelvices joined proximal to the ureteropelvic junction – the upper calyces drain into the upper pelvis, while the mid and lower calyces drain into the lower pelvis ▸ the ureters may also join distal to the ureteropelvic junction with a Y configuration (which is usually asymptomatic unless there is ‘yo-yo’ reflux precipitating recurrent infections)
Dromedary Hump
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This represents a prominent superolateral border of the left kidney (due to compression by the adjacent spleen) ▸ it may be mistaken for a renal mass
Sinus Lipomatosis
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There is increased renal sinus fat
Persistent Fetal Lobulation
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Renal tissue develops as a series of 8–16 lobules and the lobulated structure persists at birth – this feature normally disappears over the first 5 years of life as the kidney grows
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