9
Kidney and Ureter: Congenital and Acquired Anomalies
Alberto Mantovani1, Jane Hendry2, and Pankaj Mishra3
1 Great Ormond Street Hospital for Children, NHS Foundation Trust, London, UK
2 Department of Urology, Queen Elizabeth University Hospital, Glasgow, UK
3 Evelina London Children’s Hospital, Guy’s & St. Thomas’ Hospital, NHS Foundation Trust, King’s College Hospital, NHS Foundation Trust, London, UK
Abstract
Understanding the pathophysiology of congenital and acquired renal and ureteric anomalies is vital to be able to appropriate overall management. We describe the most common types of these anomalies.
Keywords: renal duplication; duplex; ectopia; horseshoe kidney; cyst; ureterocele; megaureter; pelviureteric junction (PUJ) obstruction
9.1 Introduction
In this chapter we will discuss the various congenital anomalies of kidneys and ureters. The tumours involving the upper renal tracts are described in separate chapter.
9.2 Congenital Abnormalities of the Kidney
9.2.1 Embryology
Renal anomalies are amongst the most common of all organ systems. When an ultrasound is used as screening test in healthy infants, around 3.2% are found to have genitourinary tract anomalies, half of these requiring surgery [1]. During the fourth and fifth weeks of gestation, the ureteral bud begins to develop from the distal portion of the mesonephric duct. The cranial end of the ureteric bud meets the metanephrons and continues in its cephalic migration. During this process, it forms the pelvis, calyces, and part of the collecting ducts. At the same time, the metanephros differentiates into organised renal parenchyma around the collecting system. The kidneys assume their final position at the eighth week of gestation. During ascent, they rotate 90° on the axial plane, starting with the hilum facing forward and ending with it facing medially. The blood supply changes during the migration; initially the kidneys are supplied by the middle sacral artery, then by the common iliac, and finally by the aorta [2].
9.2.2 Anomalies in Number
9.2.2.1 Supernumerary Kidney
This is a very rare anomaly due to duplication of the ureteric bud and a split mesonephric blastema. The supernumerary kidney is caudal to the ipsilateral kidney in 60% of cases. If a complete ureteric duplication occurs (around 50% of cases), the supernumerary kidney is likely to be cranial. There is usually one extra kidney, but cases of multiple extra kidneys have been reported. The supernumerary kidney has its own blood supply and capsule, is usually smaller, less functioning, and in a third of cases, is associated with other pathological changes (e.g. hydronephrosis, pyelonephritis). Many cases remain asymptomatic throughout life and are picked up incidentally on ultrasound. When complications occur, these are generally correlated with obstruction or infections and presents with typical symptoms of pain, abdominal mass, or fever [3].
9.2.2.2 Unilateral Renal Agenesis
Renal agenesis results from a failure of induction of the metanephric blastema by the ureteric bud [4]. Unilateral renal agenesis incidence is around 1:1100–1500 and occurs in similar sex ratios with a left‐sided preponderance (Figure 9.1) [5, 6]. However, foetal ultrasound series have found a much lower frequency of this anomaly, postulating that many reported adult cases of unilateral renal agenesis probably represented involuted multicystic or dysplastic kidneys (Figure 9.2) [7].
Figure 9.1 Absence of one nephrogenic ridge results in absence of all wolffian or müllerian structures.
Figure 9.2 Dysplasia: a tiny, often cystic nubbin of tissue is found at the upper end of a thin ureter.
9.2.2.2.1 Associated Anomalies
The ipsilateral ureter is absent in 50–87% of cases [8]. In case of complete ureteric agenesis, a hemi‐trigone is seen on cystoscopy. The other kidney may be affected by vesicoureteric reflux (VUR), vesicoureteric junction (VUJ) obstructions, and pelviureteric junction (PUJ) obstructions [9]. The most common associated anomalies are those of the female genitalia, with an overall incidence of 20–60% and are a result of müllerian duct anomalies [5, 10]. Most of those are asymptomatic, but hydrocolpos or hematocolpos due to a blind vagina might develop at puberty with a pelvic mass or cyclical pain or cryptomenorrhoea. The uterus is often unicornuate or bicornuate, and the ipsilateral Fallopian tube may be rudimentary or absent [11]. Vas deferens, seminal vesicle, and ejaculatory duct are absent in 50% of males with unilateral renal agenesis [11]. Around 25–40% of patients with unilateral renal agenesis have other abnormalities, most commonly within the cardiovascular and gastrointestinal systems.
9.2.2.2.2 Diagnosis
Ultrasound is the initial investigation; however renal ectopia or a hypertrophic adrenal gland can give the false‐positive presence of a small kidney. Dimercaptosuccinic acid (DMSA) renogram should be performed in all the cases of suspected agenesis. If the child is potty‐trained, a MAG3‐IRC can be useful in demonstrating possible contralateral VUR. Ultrasound of parents and siblings is recommended because a 9% incidence of asymptomatic renal malformations has been reported [12].
9.2.2.2.3 Prognosis
Hypertrophy of the single contralateral kidney occurs. Although hyperfiltration may have an adverse effect on renal function, the risk of significant renal disease is low [13]. Annual urinalysis for proteinuria and blood pressure check is reasonable.
9.2.2.3 Bilateral Renal Agenesis (Potter Syndrome)
The incidence of bilateral renal agenesis was originally reported by Potter as 1 in 4800 births [14]; however, more recently the incidence is lower and estimated at 3.5 per 100 000 [8]. The risk of recurrent Potter syndrome in subsequent pregnancies is 2–5% [15]. Oligo‐ and anhydramnios at 14–16 weeks of gestation, non‐visualisation of kidneys and non‐visualisation of urinary bladder is diagnostic on foetal ultrasound. Around 40% of the infants are stillborn and in the remaining, along with absent renal function, oligohydramnios has caused severe pulmonary hypoplasia. A characteristic fascial deformity occurs because of the lack of growth and development (Figure 9.3). The prognosis is poor, and the majority will die within 24 hours of being born. In cases of early antenatal diagnosis, termination of pregnancy is recommended.
Figure 9.3 In congenital multicystic disease, without amniotic fluid, the foetus is compressed and the face deformed (Potter facies).
9.2.3 Anomalies of Rotation
The foetal kidney faces its hilum and pelvis anteriorly, and during ascent, undergoes a 90° rotation to achieve its final normal position where hilum and pelvis face medially. Different types of anomalies of rotation are described:
- Incomplete rotation: the most common, hilum faces anteriorly;
- Hyper‐rotation: with hilum dorsal or lateral;
- Reverse rotation: hilum faces lateral and renal vessels cross the kidney anteriorly; and
- Malrotation is more frequently associated with ectopic or fused kidney and is incomplete in it its commonest form. Usually it is an asymptomatic condition, and when symptoms occur, those are generally correlated with a degree of obstruction and hydronephrosis.
9.2.4 Anomalies of Ascent
Anomalies of renal ascent and fusion occur at six to nine weeks of gestation as the kidneys seem to ascend when in fact the embryo is growing caudally. The kidney is generally abnormal in position because of insufficient or contralateral ascent (classic form of renal ectopia and crossed kidney) or because of excessive ascent (thoracic kidney, much rarer).
9.2.4.1 Renal Ectopia
Renal ectopy refers to a kidney outside its renal fossa. The ectopic kidney can be ipsilateral or can have crossed the midline when malrotation is often associated. The condition is bilateral in 10% of cases. The ipsilateral ectopic kidney is more often within the pelvis (usually below aortic bifurcation), but it can also be lumbar (above the iliac crest but below L‐2/L‐3) (Figure 9.4) [16]. Pelvic kidneys occur in 1 in 2000–3000, and the left kidney is affected more often than the right (see Chapter 3). The renal pelvis is positioned anteriorly, and there is a short ureter to the level of the sacrum. Ptotic kidney maintains a normal ureteric length and ureter can be redundant, whereas the ureter of an ectopic kidney is shorter in relation to the degree of ectopia. During ascent the blood supply changes (from middle sacral artery to iliac artery and later aorta), the final blood supply is invariably anomalous with blood vessels, which are usually short, making surgical mobilisation difficult.
Figure 9.4 DMSA (posterior view) of a three‐month‐old girl with asymptomatic, well‐functioning, left pelvic kidney: a case of simple renal ectopia.
The majority of pelvic kidneys are diagnosed incidentally, but they can be complicated by obstruction, hydronephrosis, infection, or symptoms from the presence of an ectopic ureter.
9.2.4.1.1 Diagnosis
Ectopic kidneys can be completely asymptomatic or can give symptoms due to concomitant PUJ obstruction, VUJ obstruction, and VUR. PUJ obstruction in ectopic kidneys is the result of a high ureteral insertion, malrotation, or anomalous vessels. A certain degree of slow drainage accounts for the possibility of urolithiasis. Amongst clinically significant ectopic kidneys, around 30% present with urinary tract infections (UTIs). Ultrasound can detect the ectopic kidney antenatally and postnatally. The failure to detect renal parenchyma on one side should lead to a renogram before making the diagnosis of unilateral renal agenesis. Micturating cystourethrogram (MCUG), MAG‐3, and magnetic resonance urography (MRU) should be taken into consideration in specific cases.
9.2.4.1.2 Associated Anomalies
VUR is found in 70–85% of children with an ectopic kidney [17], and the contralateral kidney is abnormal in up to 50% of patients. Contralateral renal agenesis has been found in 10% of ectopic kidneys. Genital anomalies are frequent in both sexes; in male, the most common are hypospadias and cryptorchidism. Other organs might have anomalies as well; in particular, skeletal anomalies are found in up to 50% of children.
9.2.4.1.3 Management
The most common clinical problem is PUJ obstruction. Urolithiasis might be difficult to treat because the kidney can be more distant from the skin surface, and there can be bowel interposition. Ureterorenoscopy (URS) can also be challenging if the insertion of the ureter is high in the pelvis of the ectopic kidney.
9.2.4.2 Thoracic Kidney
In a thoracic kidney, part or all of the affected renal tissue must sit above the diaphragm. This anomaly represents <5% of renal ectopy and has an incidence on autopsy of 1:13 000 (Figure 9.5) [2]. The thoracic kidney may result from an accelerated ascent process before the closure of the diaphragm or a delay in the diaphragmatic closure. It is usually completely rotated with the vascular supply arising from the abdominal aorta, and the kidney is usually well functioning. The ureter is long to compensate the distance to the bladder and PUJ obstruction has been reported [18]. Again, as generally asymptomatic, the diagnosis may be suspected at chest X‐ray for other reasons, which identify a possible mass or raised hemidiaphragm. MRU can confirm the diagnosis.
Figure 9.5 When there is a herniation of the diaphragm, the kidney may be seen in the chest, but it is not truly an ectopic kidney.
9.2.5 Anomalies of Fusion
9.2.5.1 Horseshoe Kidney
In a horseshoe kidney (HSK), the two lower poles of the kidney are joined in the midline by tissue called the ‘isthmus’. The result is the horseshoe kidney lies lower at L3/L4 compared to the normal anatomical position because the isthmus is unable to ascend past the inferior mesenteric artery. The calyces are normal in number; however, they are abnormal in position with calyces pointing posteriorly. The blood supply is often abnormal. The HSK is the most common fusion anomaly with an incidence of around 0.25% of the population (1:700) (see Chapter 3) [19].
Embryologically many theories have been postulated; certainly, there is an early medial contact between the two metanephric blastema, which can be due to a narrow passage through the space in between the umbilical arteries (arterial fork) during the ascent. The theory of ectopic metanephric blastema has also been postulated.
9.2.5.1.1 Anatomy
In 90% of the cases, the isthmus connects the lower poles of the two kidneys, and the renal units usually lie lower than normal probably because the inferior mesenteric artery stops the ascent of the HSK at the level of its origin from the aorta. However, the HSK can be anywhere from the true pelvis to the normal location. The isthmus can be functional or fibrotic. In the vast majority, the isthmus maintains some function. It is commonly in front of the great vessels but can be behind the aorta or inferior vena cava. Its blood supply is very variable. The arterial supply has been investigated deeply considering its importance in case of abdominal aortic aneurism.
It appears clear that, although renal arteries arising in a normal location are common (around 80%), extra arterial branches should be expected from the infrarenal aorta or from the iliac arteries. Other origins (e.g. medial sacral artery) are rare. The multitudes of vessels, which can supply the HSK, explain its lack of mobility.
The two renal units are usually malrotated, with the pelvis anteriorly faced because fusion happens before the completion of the rotation. The two halves of HSK can be simplex or duplex in configuration. Extrarenal calyces ending directly into the ureter with rudimentary or absent pelvis might be encountered. The ureters cross the isthmus anteriorly in the vast majority of cases. Ureters behind the isthmus are extremely rare. Moreover, the isthmus can be drained by its own calyces and independent ureter. VUJ is usually orthotopic.
9.2.5.1.2 Diagnosis
Ultrasound can identify the isthmus and make the diagnosis of horseshoe kidney even if magnetic resonance (MR) and computed tomography (CT) scans are more detailed. Radionuclide images (i.e. DMSA, MAG‐3) will delineate the functional anatomy as often the isthmus has residual function.
9.2.5.1.3 Associated Anomalies
Many associated genitourinary anomalies have been reported: VUR and PUJ obstruction are the most common anomalies in symptomatic HSK in children with an incidence, together of around 50% [20]. HSK is found with increased frequency in well‐known syndromes including Trisomy 18, Turner syndrome, and neural tube defects. Half of the HSKs are associated with extrarenal anomalies or syndromes with defects of the gastrointestinal tract and vertebral anomalies being the most common [21].
Around one‐third of HSKs remain undiagnosed throughout life [22]. PUJ obstruction is the most common pathological cause of hydronephrosis; this can be due to high ureteric insertion, anomalous blood vessels, or ureteral kinking when the ureter passes across the isthmus [23]. Urolithiasis has been found in 20% of patients with HSK, not only correlated with slow drainage but also with metabolic abnormalities [24]. Patients with HSK are at increased risk of renal carcinoid and Wilms tumour [25]. These tumours tend to arise from the isthmus, probably reflecting the abnormal migration of nephrogenic cells that occurs in this region. Renal cell carcinoma (RCC) is the most common cancer found in HSKs, but its incidence is the same of normal population [26]. Because it anatomical configuration and position, in particular the fixed position of the isthmus, the HSK is believed to be more susceptible to rupture during abdominal blunt trauma.
9.2.5.1.4 Management
Sixty percent of patients remained asymptomatic for 10 years after discovery of HSK [27]. The most common operation required for HSKs is pyeloplasty for PUJ obstruction. This can be difficult if the renal units have not completed the ascent. Both extraperitoneal and transperitoneal approaches are feasible depending on specific anatomical characteristics. The laparoscopic approach is used in adult as well as in children [28].
9.2.5.2 Crossed Renal Ectopia
In crossed renal ectopia, the kidney crosses the midline while its ureter maintains a normal ipsilateral insertion into the bladder. The incidence is around 1:7000 in autopsies [29] and the left‐to‐right crossing is more frequent. In almost all cases, the crossed kidney is fused with their mate, as the upper pole of the ectopic kidney joins the lower pole of the normal kidney.
9.2.5.2.1 Associated Anomalies
Malformations affecting other organs occur with increased frequency. VUR is common in the ectopic kidney, while ureterocoele and PUJ obstruction are less frequent. Rarely, multicystic dysplasia can affect the crossed ectopic kidney. The incidence of renal tumours in crossed renal ectopia is uncertain; RCC, mesoblastic nephroma, Wilms tumour, and primary synovial sarcoma, with RCC being the most frequent.
9.2.5.2.2 Prognosis
Thirty percent of the patients with crossed renal ectopia develop pyelonephritis or urolithiasis and 25% have hydronephrosis.
9.2.5.3 Cystic Renal Disease
Simple cysts are fluid‐filled sacs which may be single or multiple and range in size representing 70% of asymptomatic renal masses. They are mainly found in the renal cortex and do not communicate with the nephron or renal pelvis (Figure 9.6). This is in contrast to parapelvic cysts, which are simple parenchymal cysts found adjacent to the renal pelvis or hilum. Cysts may be bilateral and are increasingly prevalent with increasing age [30]. There is no definitive aetiology; however, congenital and acquired causes have been proposed, with chronic dialysis a factor in increasing formation of new simple cysts [31].
Figure 9.6 (a) It was once believed that cysts were the result of failure of a tubule to join a glomerulus. (b) In fact, Potter et al. found that in cystic disease, the nephrons were always dilated throughout their entire length.
The most common means of presentation is incidental diagnosis on imaging for another purpose. Acute presentations of severe pain can occur with bleeding into a cyst as a result of the increased pressure from distension of the cystic wall. The differential diagnosis includes RCC, early autosomal dominant polycystic kidney disease (ADPKD), or complex renal cysts (i.e. containing blood, pus or calcification.)
On ultrasound, simple cysts are defined by being anechoic, round, or spherical in shape with a smooth outline. Where there are septations, calcification, or clusters of cyst, there is indication for further investigation with contrast CT or magnetic resonance imaging (MRI) to exclude concomitant malignancy. On CT, simple cysts have no enhancement after contrast injection and have homogenous fluid density within the cyst cavity (typically −10 to +20 Hounsfield Units [HU]). Hyperdense cysts have a higher density (20–90 HU); however, they are not enhanced with contrast. The Bosniak classification is based on CT appearance of simple and complex cysts and is useful as a predictor of malignant potential with increasingly complex features [32].
A simple cyst requires no further treatment or follow up. In the rare situations where flank pain thought to be the cause, options include percutaneous aspiration with or without sclerosing agent or surgical excision of the cyst wall (Figures 9.7–9.9).
Figure 9.7 (a–d) Treatment of a renal cyst. A small window is removed from the cyst wall, and there is no need to remove the rest of its wall.
Figure 9.8 When a parapelvic cyst is obstructing a calix, it is approached though the renal sinus.
Figure 9.9 It is only necessary to remove a small window from the wall of the parapelvic cyst.
9.2.5.4 Medullary Sponge Kidney
Medullary sponge kidney (MSK) is an acquired cystic condition of the kidneys whereby there is dilatation of the distal collecting ducts with multiple cysts and diverticulum within the medulla.
Pathologically, the kidney in cross section looks like a sponge due to dilated collecting ducts and the presence of numerous cysts, which are the result of urinary stasis precipitates calculi within the cysts (Figure 9.10) [33]. As the majority of people are asymptomatic, the diagnosis is an incidental finding, and in 75%, both kidneys are affected.
Figure 9.10 Medullary sponge kidney.
CT urogram shows dilatation of the distal portion of the collecting ducts with cysts resembling ‘bristles on a brush’ or ‘bunch of grapes’ if they become filled with calcifications. Hypercalciuria may be present in a third to half of patients and advice regarding fluid and diet should be tried before considering thiazide diuretics [34]. Whilst asymptomatic MSK disease necessitates no treatment, presentations with renal colic, haematuria, and recurrent UTI range (20–60% incidence) may require treatment [35]. Renal function is maintained in the long term.
9.2.5.5 Autosomal Dominant Polycystic Kidney Disease
Autosomal dominant polycystic kidney disease (ADPKD) is the most common inheritable form of renal cystic disease and tends to becomes apparent in the third decade of life. It is an autosomal dominant–inherited disorder that results in multiple expanding renal cysts. The majority of affected individuals have a mutation either of PKD1 gene on the short arm of chromosome 16 (85%), or less often, PKD2 gene on the long arm of chromosome 4. The products of PKD1 and PKD2 are polycystin‐1 (PC1) and polycystin‐2 (PC2), and they normally act to inhibit cell proliferation. Generally, there will be sonographic evidence in all affected individuals of cysts before the age of 20. Those with PKD1 mutations tend to progress quicker than those with PKD2 mutations [36].
Because of the 50% positive family history, the presentation may be known before symptoms arise. Symptoms of palpable abdominal masses, flank pain, or macroscopic haematuria tend to present by the fourth decade of life [37]. Hypertension is present in virtually all patients [38], and rarely patients may have renal failure symptoms of lethargy, nausea, and anaemia.
With increasing age, there is in association with liver cysts, which are present endemically by the age of 50; however, these remain largely asymptomatic [39].
ADPKD contributes to 10% of all cases of renal failure [36]. The expansion cysts and resultant ischemic atrophy of surrounding renal tissue leads to end‐stage renal failure (ESRF), inevitably by the fifth decade of life. Associated extrarenal conditions include Circle of Willis berry aneurysm (10–30%), which can lead to subarachnoid haemorrhage and death in 9% [40]. The incidence of RCC in patients with ADPKD is no higher than that of the general population but is often diagnosed at a younger age. Treatment of ADPKD aims to maintain renal function and is directed at controlling hypertension with ACE inhibitors and angiotensin receptor blockers and preventing UTIs.
9.2.5.6 Autosomal Recessive Polycystic Kidney Disease
Autosomal recessive polycystic kidney disease (ARPKD) is the result of a mutation of the PKHD1 gene on chromosome 6 and is rarer than the dominant variety at 1 in 5000–40 000. When severe it manifests in utero, whilst milder cases can emerge in children up to 20 years old. Between 30 and 50% of patients can die within several days because of uraemia or respiratory compromise [41]. The early form of the disease is associated with symmetrically large kidneys that are homogeneously hyperechogenic, and then these may appear as more discrete cysts with age. Hypertension and renal insufficiency are the major manifestations in surviving children; however, liver disease from invariable congenital hepatic fibrosis, becomes more evident with age.
9.2.5.7 Acquired Renal Cystic Disease
Acquired renal cystic disease (ARCD) is associated with chronic renal failure and is most commonly seen in patients on long‐term haemodialysis and peritoneal dialysis. In contrast to simple cysts, they are in continuity with the renal tubules and are usually multiple, bilateral, and within the cortex of contracted kidneys. The cysts are hyperplastic and frequently adenomas, either of which may progress to RCC. The incidence of RCC in the dialysis population is 5–50 times that of the general population and is increased with length of time on dialysis [42]. Even if the cysts regress with transplantation, then the risk of RCC persists, albeit at a much lower level [43].
Investigation is focussed on the presenting symptom. If haematuria is persistent as it may be in patients on heparinised dialysis, then the options of transfer to peritoneal dialysis, renal embolization, or nephrectomy of nonfunctioning kidneys should be considered. Where malignancy is suspected, the options of nephrectomy or surveillance should be based on symptoms and likelihood of malignancy. Due to the high risk of development of RCC, there is indication for surveillance ultrasound or CT of patients with ARCD on dialysis.
9.3 Congenital Abnormalities of the PUJ
9.3.1 Hydronephrosis
Hydronephrosis is defined as an abnormal dilatation of the pelvis with or without associated calyceal dilatation. Hydronephrosis is found in around 1% of pregnancies and is caused by PUJ obstruction in 10–30% of cases.
9.3.2 PUJ Obstruction
PUJ obstruction is generally the result of a primary intrinsic defect of the ureteric muscular layers where there is an aperistaltic segment of ureter. Crossing vessels have been noted in up to 63% of adult with PUJ obstruction and only in 20% of patients with normal kidneys [44]. However, historically it is thought that it is truly an intrinsic lesion defect and the crossing vessel may be incidental [45].
Symptoms varies from UTIs and flank pain, even if the diagnosis is currently made very early by ultrasound and usually during pregnancy. Generally, the typical diagnosis shows decreasing differential renal function and increasing hydronephrosis with or without symptoms. In adults, the classical presentation is of flank pain precipitated by a diuresis but may also be associated with a flank mass or recurrent UTI. However, many PUJ obstructions lack to manifest all the typical features.
Renal ultrasound shows a dilated renal pelvis in the absence of a dilated ureter. CT urogram demonstrates a delay in excretion of contrast and a dilated renal pelvis. MAG 3 renogram with diuretic is the gold standard for showing radioisotope accumulation in the pelvis, and following furosemide, there continues to be a rising curve as contrast remains in the renal pelvis.
Indications for intervention include symptoms associated with obstruction, impairment of overall renal function or progressive impairment of ipsilateral function, and development of stones or infection. Only a third of children with PUJ obstruction will require intervention [46]. Pelvic AP dilatation >3 cm is also a strong indicator of intervention for PUJ obstruction. Poor drainage after the administration of furosemide, increased anteroposterior diameter on the ultrasound, and grades III and IV dilatation as defined by the Society for Foetal Urology (Table 9.1) are also strong indicators. PUJ obstructions with a residual function <10% should be approach carefully because successful repair for poor functioning kidneys is more difficult to achieve, and nephrectomy should be considered. The diagnosis is completed confirmed with ultrasound and MAG3 (Figure 9.11) [46].
Table 9.1 The SFU‐Grading System for Hydronephrosis takes into account three parameters: dilatation of renal pelvis, dilatation of calyces, and thickness of parenchyma.
| SFU‐grade | Description |
| 0 | No hydronephrosis |
| 1 | Only renal pelvis visualised |
| 2 | Dilatation of pelvis |
| Dilatation of pelvis + major calyces | |
| 3 | Grade II + minor calyces |
| 4 | Grade III + thinning of parenchyma |
Figure 9.11 Ultrasound showing calyceal dilatation on a two‐month‐old girl with pelviureteric junction obstruction.
9.3.2.1 Surgical Correction
The armamentarium for the surgeon is wide and effective as different techniques and approaches have been described. The generally adopted technique is the Anderson‐Hynes dismembered pyeloplasty, described in 1949, with success rates currently consistently >90% [47]. This operation can be completed using open (i.e. flank, posterior lumbotomy, subcostal), laparoscopic (i.e. transabdominal, retroperitoneal), or robotic approaches [48]. Minimally invasive approaches, including robotic, have shown a low perioperative complication rate, a short hospital stay, and success rates of >95% [49]. As yet there is no randomised trial comparing open to laparoscopic and robotic pyeloplasty. Other techniques for pyeloplasty, like the Foley Y‐V plasty or the Davis intubated ureterotomy, have declined in popularity. Endoscopic incision or dilatation of the PUJ (either antegrade or retrograde) have been reported with overall less successful rates compared to dismembered pyeloplasty and are now prevailing in cases of recurrent PUJ obstructions after failed pyeloplasty [50]. Endopyelotomy might be challenging in failed pyeloplasty, if the length of the stricture is >1 cm. For children, redo laparoscopic pyeloplasty has been used effectively but may be a difficult operation because of scarring [51].
In children, the debate exists regarding the need of a transanastomotic stent (nephrostomy or double‐J) in the postoperative period after pyeloplasty, given another anaesthetic is required for removal. However, a longer hospital stay because of the management of complications like urine leak and clot obstruction has been reported when the stent was avoided [52]. In adults, a stent is generally placed for four to six weeks postoperatively, and subsequent MAG3 renogram is used to demonstrate improved obstruction. Most failures of surgery, either of symptom persistence or lack of radiographic improvement occur within two years of surgery although 30% of failures occur later [53]. Failed pyeloplasty refers to either persistent obstruction or its recurrence due to anastomotic stricture and it occurs in 2–6% of cases. The laparoscopic approach has shown high effectiveness for redo pyeloplasty [53].
9.3.3 Congenital Abnormalities of the Ureter
The ureter may fail to develop or can partly develop or can abnormally develop. Also, failure of developing duplication ureters may lead to blinded‐ending ducts with ureteric orifices or an aberrant ureter (Figures 9.12–9.14).
Figure 9.12 Cystoscopic findings in agenesis: there is no ureter on one side.
Figure 9.13 At the lower end of the ureter, there are often a number of blind‐ending ducts, presumably attempts at formation of ureteric buds.
Figure 9.14 An aberrant ureter may end in a blind‐ended pouch.
9.3.3.1 Duplex System
A duplex system refers to a single kidney functionally divided into two moieties (upper and lower) draining independently into two pelvicalyceal systems. Those systems can join together before the PUJ (bifid system) (Figure 9.15) or beyond it but above the bladder (incomplete duplex) or be completely separated with two distinctive ureters with two separate ureteric openings (complete duplex).
Figure 9.15 Diagram of a duplex kidney in which the ureters divide about half way up to the kidney.
The Wiegert–Meyer rule dictates that the upper pole ureter opens onto the bladder medially and distally to the upper pole moiety ureter which opens laterally and proximally (Figure 9.16) [54]. Therefore, the upper pole moiety ureter with its long intramural course is predisposed to obstruction, whilst the lower pole moiety with reduced intramural ureteric length is susceptible to reflux in 85% of cases.
Figure 9.16 When there is complete duplication, the ureter from the upper half‐kidney always enters the bladder caudal to the ureter from the lower half.
Unilateral cases of renal duplication are more common than bilateral with a higher female to male ratio of 2:1. The overall incidence is 1 in 125 and both sides are affected equally. The presentation may be an incidental finding, UTI symptoms or recurrent, flank pain (Figure 9.17).
Figure 9.17 Diagram of see‐saw reflux: the urine from the lower moiety of the duplex kidney passes up to the upper calix causing distension and pain; urine stasis can lead to infections and reinfections.
Investigation with ultrasound shows ureteric duplication with the possibility of dilatation. The CT urogram findings of a ‘drooping lily’ arise due to decreased contrast excretion from an obstructed renal upper pole, displacing the lower pole downwards and laterally. The definitive test of reflux is a micturating cysto‐urethrogram and a 99mTc‐ DMSA renogram assesses renal function.
Treatment depends on symptoms and whether reflux or obstruction is the main issue.
9.3.3.1.1 Embryology
The ureteric bud which arises from the mesonephric duct meets the metanephrons to form the kidney as the result of the bidirectional induction between the two structures. To develop normally, the ureteric bud needs to arise and reach the metanephrons in the correct area. The farther the ureteric bud joins the metanephrons from the normal region, the more significant the degree of renal dysplasia will be. The ureteric bud will originate the entire collecting system. If it branches before to reach the metanephrons, the result will be an incomplete duplex or a bifid system. If two ureteric buds arise from the mesonephric duct, there will be a complete duplex; initially, the proximal ureteric bud will meet the metanephrons above the other to form the upper moiety, but then, during the process of rotation to establish the final junction between ureters and bladder, the proximal ureter will move more caudal compared to the ureter draining the lower moiety. The result is that, in a complete duplex, the caudal ureteric orifice (UO) drains the upper moiety as explained by the Weigert‐Meyer rule. The ureter draining the upper moiety can insert within the bladder or more caudally, into structures derived from the mesonephric duct; whatever the level of insertion is, those ureters are called ‘ectopic’. Clinically, the main difference between ectopic ureter in men male and women female is that for the former the UO of an ectopic ureter is always above the urethral sphincter, providing the maintenance of urinary continence. In females, the ectopic ureter can insert below the urethral sphincter, leading to various degree of incontinence. The ureter draining the lower moiety tends to insert more laterally, with a shorter intramural tunnel and hence more prone to reflux.
9.3.3.1.2 Pathophysiology and Management
Duplex system can be clinically asymptomatic or be affected by different pathological conditions:
VUR is a frequent finding in duplex with an incidence, in children presenting with UTIs, around 70% [55]. VUR affects mostly the lower moiety ureter because of its short intramural course; however, both ureteric orifices can be refluxing.
VUR has similar spontaneous resolution rates compared to simplex systems. Indications for surgical correction, especially for those with high grade reflux, are scar formation or recurrent UTIs (failure of medical treatment).
Treatment can be ureteric reimplantation (i.e. open, laparoscopic, vesicoscopic), uretero‐ureterostomy (open, laparoscopic), or endoscopic injection of bulging agents. Endoscopic treatment has shown similar successful rate (64%) for VUR in duplex kidneys compared to single systems [56]. If the affected moiety shows poor function and is dilated, then hemi‐nephro‐ureterectomy is the option (either open or laparoscopic).
9.3.3.2 Ectopic Ureter
The ureteric orifice arises below the normal insertion point of the trigone of the bladder. The majority of cases hare associated with a duplex collecting system and are caused by the ureteric bud arising from an abnormal position on the mesonephric duct. As the upper pole as previously described always enters distal and medial to the lower pole ureter, upper pole ureters are predisposed to ectopic placement (Weigert‐Meyer rule.) The sites of ectopic ureters vary in females from bladder neck, urethra, and vagina and in males from posterior urethra, seminal vesicles, ejaculatory duct, vas deferens, or bladder neck (Figure 9.18). It is three times more common in females than males. The presentation is usually in both sexes with acute or recurrent UTI. In females when the opening lies below the urethral sphincter, girls present with persistent vaginal discharge or incontinence. In males, the ureter always sits above the external urethral sphincter; therefore, there is no incontinence.
Figure 9.18 The ureter from the upper half‐kidney may open into the vagina below the sphincter and cause incontinence.
The farther is the UO form the orthotopic position, the higher is the degree of dysplasia affecting the renal moiety drained by that ureter [57]. Recognising an ectopic ureter might be very difficult, and a high index of suspicious is required. In suspected cases of ectopia, it is not unusual and requiring an MRU to have the best anatomical details. Even with this, poor functioning and small upper‐pole moieties can be difficult to visualise (cryptic duplex). MCUG and cysto‐vaginoscopy may or may not help to identify the ectopic ureter or UO, respectively. Once the diagnosis is established, the surgical treatment depends on the functional contribution of the upper‐pole moiety and symptoms. If poor functioning, upper‐pole hemi‐nephrectomy is indicated. If a reasonable function is preserved, then ureteric reimplantation (of both the duplex system ureters) or uretero‐ureterostomy can be performed.
Bilateral ectopic ureters affect girls, and the challenge is not only to correct the insertion of the ureters with ureteric reimplantation, but mostly to manage the small bladder and poor sphincteric mechanism that the bilateral ectopia has induced.
9.3.3.3 Ureterocele
Ureterocele represents a cystic dilatation of the terminal ureter into the bladder. The most adopted classification distinguishes the ureterocele into two types: orthotopic and ectopic. An orthotopic ureterocele arises entirely from the normal location of its UO; it is contained within the bladder, but it can prolapse at the bladder neck or beyond. The ectopic ureterocele has part of its wall arising from an abnormal location, usually the bladder neck. The ectopic type is most commonly associated with the upper moiety of a duplex kidney and may cause obstruction (Figure 9.19). The diagnosis is reached by the combination of ultrasound and MCUG. Cystoscopy might be required to delineate the exact anatomy. DMSA is indicated to assess the functional contribution of the upper moiety draining into the ureterocele.
Figure 9.19 (a and b) A ureterocele may prolapse through the urethra and cause obstruction.
The treatment varies depending on symptoms, function, degree of obstruction, and ureterocele type (Figure 9.20). Conservative management is an option in an asymptomatic child with a good to poor functioning upper moiety draining into a nonobstructing ureterocele. Leaving poor functioning or dysplastic parenchyma does not increase the risk of hypertension [58].
Figure 9.20 A ureterocele may cause (a) obstruction and (b) the formation of a calculus.
Endoscopic ureterocele puncture has the advantages of the minimal‐invasive approach. The need of further surgeries might be very high [59], and the most common reason for reoperation is VUR. There is no consensus in surgical management of ureterocele; however, endoscopic puncture has achieved the favour of many in case of emergency decompression of an infected or obstructed ureterocele. Upper pole hemi‐nephroureterectomy can be considered if there is poor or no function in the upper moiety. Uretero‐ureterostomy is a relatively simple procedure which can be performed laparoscopically or be laparoscopically‐assisted with minimal tissue mobilisation. Following failed ureterocele puncture in infancy, ureterocele excision/bladder neck reconstruction is a difficult surgery.
Single system ureteroceles are mostly orthotopic, and the corresponding kidney usually shows reasonable residual function. Conservative management is acceptable if no obstruction is suggested, otherwise the endoscopic approach is usually successful, with a low rate of further surgeries. Generally surgical ureteric reimplantation follows incision of the ureterocele to preserve renal function and prevent reflux.
9.3.3.4 Megaureter
Megaureter refers to an abnormal dilatation of the ureter, with or without hydronephrosis. Any dilatation of the retrovescical ureter ≥7 mm from the 30th week of gestation onward is considered abnormal [60]. Megaureter can be classified pathophysiologically into four categories: obstructive, refluxing, reflux with obstruction, and non‐refluxing and non‐obstructing.
9.3.3.4.1 Diagnosis and Work‐Up
A predictive value of a megaureter detected antenatally has not been established yet [61]. The only current recommendation is to monitor it postnatally if ≥7 mm. As the hydroureteronephrosis carries an increased risk of UTI; antibiotic prophylaxis is advisable [62]. Postnatally, the first investigation should be ultrasound followed by MCUG in all the cases of ureteric dilatation. Irrespective of bilateral or unilateral hydroureteronephrosis in a male infant, the MCUG should be done early (around 14% of males with unilateral hydroureteronephrosis have posterior urethral valves) [63]. The possible obstructive component of a megaureter is the most dangerous for the kidney; therefore, prompt diuretic renogram is indicated in case of isolated ureteric dilatation >10 mm. Interpretation of the MAG3 can be difficult because delays in drainage might be seen in the absence of obstruction due to the nature of the redundant ureter or capacious pelvis. The result should be therefore interpreted based on both clinical and radiological data. In an asymptomatic patient, an initial differential renal function of 40% or a drop by 5% on serial scans should indicate an element of obstruction. Contrariwise, delayed drainage at MAG3 with stable or improving dilatation on ultrasound and normal differential renal function in an asymptomatic patient do not indicate the need of urgent intervention.
Conservative management of primary obstructing megaureter (POM) is well established in the literature with more than 70% of patients not requiring surgery at long term follow‐up [64]. Indications for intervention are drop or reduced differential renal function, breakthrough UTI, pain, or worsening dilatation. Ureteric reimplantation (with or without tapering) is the definitive treatment. In experienced hands, the reimplant can be performed before the first year of age [65]. Otherwise it can be postponed and a temporising procedure can be undertaken such as double‐J stenting, cutaneous ureterostomy, endoureterotomy, or endoscopic balloon dilatation. Late complications of conservatively treated POMs have been reported during the adult life, suggesting that follow‐up is still needed after childhood [66].
9.3.3.5 Retrocaval Ureter
Retrocaval ureter is a rare entity where the course of the ureter becomes posterior to the inferior vena cava at the level of L3–L4 (Figure 9.21). It is the result of the inferior vena cava developing from the subcardinal system (which lies anteriorly to the ureter during the foetal life) instead of the supracardinal system (which lies posteriorly). Its prevalence is around 1:100 live births and is more common in males. It occurs as a result of the persistence of the cardinal veins. Usually it presents in the third to fourth decades of life with flank pain, haematuria, UTI, or urolithiasis. The ultrasound shows hydronephrosis along with proximal ureteric dilatation. MAG3 renogram confirms the degree of obstruction and MRU defines the anatomy and suggests the diagnosis. Based on previous intravenous urogram (IVU) series, there may be an ‘S Shaped’ or ‘sickle shaped’ curve of the ureter, with the point of obstruction coinciding with the lateral margin of the inferior vena cava [67].
- Moderate to severe hydronephrosis with ‘S’ or ‘fish‐hook’ deformity of the ureter at the point of obstruction. The point of obstruction has some distance from the lateral margin of the IVC.
- Mild hydronephrosis with ‘sickle‐shaped’ curve of the ureter at the point of obstruction. The obstruction coincides with the lateral margin of the inferior vena cava.
Figure 9.21 Diagram of retrocaval ureter.
Retrocaval ureters requiring surgery are mostly treated by uretero‐ureterostomy either approached open or laparoscopically (Figure 9.22).
Figure 9.22 (a–d) Operation for a retrocaval ureter: there is no need to remove the narrow segment of ureter from behind the vena cava. A long elliptical anastomosis is made between the redundant pelvis and the ureter.
9.3.3.6 Congenital Abnormalities of VUJ
VUJ obstruction, even if anatomically belonging to the junction itself, has been described in the paragraphs dedicated to megaureter, which represents the radiological and clinical manifestation guiding the management.
9.3.3.6.1 VUR
VUR refers to the retrograde flow of urine from the bladder up to the ureter or kidney. The incidence in children is around 10%, with higher rates in younger, Caucasian, and females. Because an affected child has a 40% of a sibling being affected as well, screening of siblings is recommended. Amongst children presenting with UTI, around 30% are found to have reflux [68]. When the ureter passes through the bladder wall the muscular attachments prevent reflux. Therefore, when the intramural ureter is short (ratio of intramural ureter length to diameter of ureter <5:1) reflux occurs. VUR when associated with UTI can result in reflux nephropathy, hypertension, and progressive renal failure. In adults, 25% of patients requiring renal replacement therapy do so because of reflux nephropathy. The presentation is generally with symptoms of UTI but can be more general with abdominal pain, failure to thrive, or vomiting. In adults, VUR may be asymptomatic, a cause of loin pain associated with a full bladder, or recurrent UTI.
VUR can be classically divided into two main subtypes: primary, due to a shorter intravesical tunnel at the VUJ, and secondary, due to other pathological conditions (e.g. posterior urethral valves, neurogenic bladder, detrusor sphincter dysynergia) which increase the intravesical pressures. In adults, secondary VUR may occur iatrogenically following ureteric meatotomy for the removal of ureteric stones at the VUJ. It also arises in duplex systems where the lower pole moiety with a shorter intramural course is predisposed to VUR.
VUR has been classified, based on the degree of the retrograde flow of urine, into five grades [69]:
- Grade I: reflux into the ureter only
- Grade II: reflux into a nondilated pelvi‐calyceal system
- Grade III: dilatation of the collecting system
- Grade IV: more dilation with blunting of the calyces and tortuosity of the ureter
- Grade V: massive dilation of the collecting system and severe tortuosity of the ureter
The grade of the VUR has been found the most important factor in determining the likelihood of spontaneous resolution, even if other variables can be put into the equation to finally estimate the specific risk for each patient (e.g. age, gender, laterality, bladder behaviour, renal scarring, and number of UTIs.)
Diagnosis
VUR is clinically suspected and subsequently confirmed with radiological investigations. The gold standard is the MCUG, on which the grading scale is based. After the age at which a child is toilet trained, an alternative to MCUG is the MAG3‐IRC (MAG3 with indirect radionuclide cystography), where the captured images continue during the micturition, to detect the concurrent radionuclide activity back to the ureter or kidney. MAG3‐IRC is less invasive but less sensitive. Ultrasound can identify reflux, especially if the difference between the ureteric dilatation before and after the micturition is evident. For the evaluation of renal scars, DMSA is historically adopted, even if MAG3 seems to have the same sensitivity [70].
Treatment
Large debate exists in regards to the need for and treatment modalities for VUR. Various treatment modalities like no active treatment, prophylactic antibiotic, endoscopic treatment, and reimplantation (i.e. open, laparoscopic, vesicoscopic) have all showed to be of value depending on the cohort of patients analysed.
VUR Treatments in Children
The rationale of any algorithm for the treatment of VUR is based on:
- 1) The formation of new renal scars is due to the presence of infected urine reaching the kidney [71].
- 2) VUR, especially low grade, has high chances of spontaneous resolution
Undoubtedly, there is a subgroup of patients who could be observed safely even if the first presentation was UTI. The assumption that the VUR is always the cause of the UTI might be wrong in some cases as the likelihood of UTIs in the presence of a low‐grade reflux without any stasis of urine in the upper tract is minimal.
The daily administration of antibiotic prophylaxis until the spontaneous resolution of the VUR is a widely used strategy. The RIVUR trial found a significant decreased number of recurrent UTI in patients with VUR who received prophylaxis compared to the placebo group, even if there was no difference in the risk of renal scarring [72]. Whilst the Swedish reflux trial, which included children aged 12–23 months with grades III–IV reflux, showed a benefit of prophylaxis in diminishing the incidence of UTI and renal scar formation only in girls [73]. Antibiotic prophylaxis needs good compliance from the family and regular follow‐up from the clinician to catch breakthrough UTIs promptly.
Surgical Treatment
Surgical treatment is generally indicated in case of breakthrough UTIs, development of new scars, or symptoms. If a VUR has not resolved spontaneously after conservative treatment the cut‐off age for surgery is usually around five years, but the timing is absolutely individualised.
The endoscopic injection of dextranomer/hyaluronic acid copolymer (Dx/HA) Deflux®, has achieved popularity with time as the VUR can be treated as a day case. The overall successful rate of endoscopic injection is about 70%. The procedure can be repeated if indicated, with improved efficacy however this is not replicated in a third injection. The two most widely adopted techniques are the STING (originally meaning ‘subureteral Teflon injection’) and the hydrodistention injection technique (HIT), with its modifications of double‐HIT and triple‐HIT. The main difference is that with the STING the injection is made just outside the ureteric orifice, usually at 6 o’clock, while with the HIT the injection is made into the ureter beyond the ureteric orifice.
The rate of complications is low: ureteric obstruction occurs with an incidence of around 0.7%. The reflux can be resolve completely or step down to a lower degree; the long‐term outcome is difficult to estimate as the distal ureter can improve its anatomy spontaneously, contributing to the long‐term effect. The Dx/HA has shown less tendency to migrate with time compared to other materials previously used.
Ureteric reimplantation surgery has reported successful rates of >95%. When done open, the approach is usually through a Pfannenstiel incision. Many techniques have been described to reimplant the ureter, and they can be divided into two types: extravesical (e.g. Lich‐Gregoir) and intravesical (e.g. Cohen, Politano‐Leadbetter) reimplantation. Specific complications include recurrence, UO stenosis, and bladder dysfunction (especially for extravesical bilateral reimplantation). The length of the new ureteric tunnel should be five times the diameter of the ureteric lumen [74].
VUR Treatment in Adults
In adults with primary VUR and recurrent UTI who have no symptoms in between the infection, treatment should be directed at UTIs when they occur, with the added option of low‐dose prophylaxis if the frequency of UTIs increases. If there is regular pyelonephritis or deterioration in renal function or progressive radiological signs of reflux, then reimplantation should be considered. When there is minimal function in the affected kidney (<10%), nephrectomy should be considered. For secondary reflux into a transplanted kidney no treatment is required.
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