(1)
Pediatric Surgery, AlSadik Hospital, Qatif, Saudi Arabia
3.1 Introduction
Pelviuureteric junction (PUJ) obstruction is a partial or complete blockage of the flow of urine from the renal pelvis into the ureter (Fig. 3.1).
Fig. 3.1
Diagrammatic representation of PUJ obstruction (Note the dilated renal pelvis and calyces of the kidney and the area of narrowing that usually causes partial obstruction to the flow of urine from the renal pelvis to the ureter)
This results in accumulation of the urine in the renal pelvis leading to its dilatation and back pressure on the renal parenchyma leading to progressive renal damage and deterioration.
PUJ obstruction is the most common cause of antenatally detected hydronephrosis and the most common cause of pediatric hydronephrosis.
Ultrasonography reveals fetal upper urinary tract dilatation in approximately 1 in 100 pregnancies; however, only 1 in 500 are later diagnosed with significant urologic problems.
PUJ obstruction is found in approximately 50 % of patients diagnosed with antenatal hydronephrosis.
The reported incidence of PUJ obstruction is 1 in 500 live births. Others report the estimated incidence of PUJ obstruction as 1 per 1,000–2,000 live newborns.
The widespread use of antenatal ultrasonography has contributed to an increase in the number and earlier diagnosis of hydronephrosis.
PUJ obstruction is commonly seen in infants and children and less commonly in adults.
PUJ obstruction is found more commonly in boys than in girls. The male-to-female ratio of UPJ obstruction is 3–4:1.
PUJ obstruction occurs more on the left side than on the right. The left kidney is affected in 67 % of cases and the right kidney in 33 % of the cases.
Bilateral PUJ obstruction is seen in about 10 % of the cases. Bilateral PUJ obstruction (synchronous and asynchronous) is seen in 10–40 % of infants <6 months.
Less than 5 % of patients with bilateral PUJ require bilateral repair because of spontaneous resolution in a significant number of cases.
With the current routine use of antenatal ultrasound, most cases of congenital pelviureteric junction obstruction are diagnosed antenatally.
PUJ obstruction may be diagnosed at any age.
Some of these cases may be asymptomatic discovered incidentally during evaluation of some other unrelated problem.
PUJ may be identified during the investigation of intermittent flank or abdominal pain, urinary tract infection, hematuria.
Symptomatic cases may present with intermittent flank or abdominal pain that is made worse by drinking large amounts of fluids or they may present with an abdominal or flank swelling.
The cause is usually a congenital abnormality in the pelviureteric junction leading to its narrowing.
Other causes of intrinsic PUJ obstruction include:
Valvular mucosal folds
Persistent fetal ureteral convolutions
Ureteral polyps
In about 10 % of children with PUJ obstruction, an aberrant or accessory renal artery or arterial branch may cross the lower pole of the kidney, resulting in compression of the PUJ and blockage of urinary flow.
In some cases, the obstruction may be acquired following injury to the pelviureteric junction leading to its narrowing. This is usually secondary to inflammation related to a stone stuck at the junction.
PUJ obstruction is known to be associated with other urological anomalies and these include:
Renal dysplasia
Contralateral multicystic dysplastic kidney
Contralateral renal agenesis
Duplicated renal collecting system, in which case the lower pole system is usually the obstructed segment
Horseshoe kidney
Ectopic kidney
Vesicoureteral reflux (up to 40 %)
The degree of obstruction is variable ranging from mild to severe.
Mild degrees of PUJ obstruction do not require any surgical treatment, and these patients can be followed up hoping for complete spontaneous relive of obstruction.
Symptomatic patients and those with impaired renal function require surgical intervention to preserve the remaining function of the kidney.
The first reconstruction of an obstructed kidney was made in the late 1800s by Trendelenburg.
In 1936, Foley described the YV-plasty to repair PUJ.
In 1946, Anderson and Hynes described their operation to treat PUJ obstruction. This is now the standard operation used to repair PUJ obstruction and bear their name (The Anderson-Hynes dismembered pyeloplasty).
3.2 Embryology
The ureter develops from the ureteral bud.
It extends upward towards the developing kidney.
Induction of the metanephric blastema has been thought to be mediated by the ureteral bud through several factors including:
Transcription factors such a Pax-2
Growth factors such as c-ret, kdn-1, and wt1
Transforming growth factor β (TGFβ).
Embryologically, the pelvi-ureteric junction forms usually around the fifth week of intra-uterine life.
At around the 10th–12th weeks of intra-uterine life, the initial solid tubular lumen of the ureter becomes reanalyzed.
It has been suggested that the ureteropelvic and ureterovesical portions of the ureter are the last to canalize.
Failure of canalization or partial canalization is thought to be the main embryological explanation of a PUJ obstruction.
Another theory suggests arrest of ureteral wall musculature development leading to the persistence of an aperistaltic segment at the PUJ level leading to partial obstruction.
Another theory suggests improper innervation with diminished synaptic vesicles at the PUJ which may play a role in the development of PUJ obstruction. This was supported by the findings of decreased amounts of the several factors in the resected specimens of PUJ. These include:
Protein gene product (PGP) 9.5 (a general neuronal marker)
S-100 protein (a nerve supporting cell marker)
Synaptophysin (a synapse vesical marker)
Nerve growth factor receptor
Early in the embryological development, the proximal ureter is folded on itself and persistence of the unfolding may contribute to the kinked appearance of the proximal ureter.
The most attractive theory is that the PUJ obstruction is secondary to muscular discontinuity. This disrupts the coordinated smooth muscles movement and disrupt peristalsis propagation across the PUJ. The end result is a narrow but structurally patent lumen at the PUJ which in the presence of high urine volume cannot efficiently empty. This is supported by the followings:
The findings of rearrangement and widely separated smooth muscle cells
The findings of excessive collagen fibers
The findings of increased elastin in the adventitia
The findings of diminution of nerve terminals and nerves at the stenotic portion.
3.3 Pathophysiology
The drainage of urine from the renal pelvis to the ureter depends on several factors.
Pressure within the renal pelvis is determined by the volume of urine produced
The internal diameter of the PUJ and collecting system
The compliance of renal pelvis
The peristaltic activity of the ureter
In response to the increased urinary volume and pressure, the renal pelvis dilates.
The effect of this on the renal parenchyma may be quite variable.
Sometimes and despite of massive dilation of the renal pelvis, preservation of renal function may occur.
A pressure-dependent flow:
This is seen in those with intrinsic obstruction where at low urinary flow rates, no obstruction exists; but as the urinary flow rate increases, urinary stasis will develop leading to dilatation of the renal pelvis.
A volume-dependent flow:
This is seen in those with extrinsic obstruction usually caused by aberrant vessels. There is a normal urine flow which is impeded only after a definite amount of urine is collected in the renal pelvis.
Patients with extrinsic obstructions tend to present late in childhood, with intermittent abdominal or flank pain.
The degree of renal damage generally is less than that of intrinsic obstruction because the pressure damage is only evident intermittently.
This obstructive nephropathy is progressive if the PUJ obstruction is not relived and this manifest in progressive deterioration of the renal function (Figs. 3.2 and 3.3).
Figs. 3.2 and 3.3
Abdominal CT-scan in two children with PUJ obstruction (Note the sever renal atrophy in the first CT as a result of progressive dilatation of the renal pelvis and pressure on the renal parenchyma while in the second one there is relative preservation of the renal parenchyma)
Sometimes, the obstructive nephropathy will progress and becomes irreversible in spite of relive of the PUJ obstruction.
There is also activation of the renin-angiotensin system and administration of the angiotensin-converting enzyme (ACE) inhibitors has been shown to maintain renal blood flow and prevent the histologic changes of glomerulosclerosis.
The long-term effects of PUJ obstruction on the kidney are quite variable and depend on several factors including:
The variability in the degree of obstruction
The timing of the obstruction
The ability of the renal pelvis and renal collecting system and renal parenchyma to adjust to the changes associated with obstruction.
Early PUJ obstruction causes severe malformation of the kidney (dysplasia), whereas late occurring PUJ obstruction may not affect the kidney as severely.
3.4 Etiology of PUJ Obstruction
There are several causes of PUJ obstruction and these can be divided into two groups, primary and secondary causes.
Primary causes include (Figs. 3.4 and 3.5):
Figs. 3.4 and 3.5
Contrast studies through a nephrostomy tube for two children with PUJ obstruction (Note the normally inserted ureter in the right picture and the highly inserted ureter in the left picture. Many feel that the high insertion of the ureter is secondary to the dilated renal pelvis rather the primary cause of PUJ obstruction)
Intrinsic obstruction from stenosis at the PUJ due to scarring of ureteral valves.
An abnormal or high insertion of the ureter into the renal pelvis. This is controversial ad many consider this a secondary phenomenon to obstruction.
Ureteral hypoplasia may result in abnormal peristalsis through the PUJ.
Asymmetry of ureteral wall musculature may inhibit the natural peristaltic emptying of the renal pelvis into the ureter.
Secondary causes include (Figs. 3.6, 3.7, 3.8, 3.9, 3.10, 3.11 and 3.12):
Figs. 3.6 and 3.7
Contrast studies through a nephrostomy tube in two children with PUJ obstruction (Note the kinked ureters in both but it is difficult to decide whether this is the cause or it is secondary to PUJ obstruction)
Figs. 3.8, 3.9, and 3.10
A contrast study and intraoperative photographs of a child with a hydronephrotic pelvic kidney secondary to PUJ obstruction that was also malrotated
Figs. 3.11 and 3.12
Intraoperative photographs showing hydronephrosis secondary to an aberrant lower polar vessel. Note the vessel compressing the ureter in the upper photograph. Note also the associated hydronephrosis following division of the ureter
Crossing lower-pole renal vessel(s).
Fibrous bands
Kinks
Horseshoe or pelvic kidney
Duplex collecting systems
Rotational abnormalities of the kidney
Renal hypermobility can cause intermittent obstruction that is solely dependent on the position of the kidney relative to the ureter.
Secondary PUJ obstruction can be caused by prior surgical intervention to treat other renal disorders (e.g., renal stone)
Failed repair of a primary PUJ obstruction.
Inflammation at the PUJ secondary to an obstructing stone.
Ureteral-wall and periureteral scar formation as a result of inflammation or prior surgical repair.
Aberrant polar vessels may also cause compression and obstruction of the PUJ.
The end result of PUJ obstruction depends on the severity of obstruction. This will lead to the following changes:
Impaired urinary drainage
Elevated intrarenal back pressure
Dilatation of the renal pelvis and collecting system, and hydronephrosis
Back pressure on the renal parenchyma
Progressive renal damage and renal deterioration
3.5 Clinical Features
PUJ obstruction is the most common cause of neonatal and antenatal hydronephrosis, occurring in 1 per 1,000–1,500 live births.
The presentation of PUJ obstruction is also variable.
Neonates with PUJ obstruction are usually asymptomatic and the majority present with hydronephrosis that was diagnosed in utero by an antenatal ultrasound.
Prior to the use of prenatal ultrasonography, most patients with PUJ obstruction present with:
Pain
Hematuria
Urinary tract infection
Failure to thrive
A palpable mass
Currently, with the availability and routine use of prenatal ultrasonography, urologic abnormalities including PUJ obstruction are being diagnosed earlier and more frequently.
50 % of patients diagnosed with antenatal hydronephrosis are eventually diagnosed with PUJ obstruction upon further workup.
Fetal and neonatal hydronephrosis:
Most cases of PUJ obstruction are diagnosed antenatally during routine antenatal ultrasound.
These cases are confirmed by postnatal ultrasound.
Newborns may present with:
A palpable abdominal mass caused by an enlarged obstructed kidney.
Urinary tract infection
Hematuria
Failure to thrive
Renal failure is an unusual presentation, and occurs in infants with a single obstructed kidney or with bilateral severe hydronephrosis.
Older children may present with:
The presentation of patients with PUJ is variable depending on the severity of obstruction.
Intermittent back pain, flank pain or abdominal pain
The pain may worsen during brisk diuresis
Abdominal pain may be accompanied by nausea and vomiting
A detailed history may reveal that the pain correlates with periods of increased fluid intake or ingestion of a food with diuretic properties (i.e. Dietl’s crisis).
Urinary tract infection
A flank mass representing the hydronephrotic kidney
The enlarged kidney is vulnerable to traumatic injury (Figs. 3.13, 3.14 and 3.15)
Figs. 3.13, 3.14, and 3.15
Abdominal CT-scans showing trauma and rupture of a hydronephrotic kidney in a child with PUJ obstruction
Hematuria
Renal calculi
Hypertension
An incidental finding on abdominal ultrasound evaluation
Initially, most children diagnosed to have PUJ obstruction are treated conservatively and monitored closely.
Surgical intervention is indicated in symptomatic patients and those with significantly impaired renal drainage and decreased renal function.
The presence of significant hydronephrosis on antenatal ultrasound is based on the followings:
The anteroposterior diameter of the renal pelvis is more than 10 mm.
The ratio of the renal pelvis to the anteroposterior kidney is more than 0.3.
Evidence of caliectasis is present after 24 weeks of gestation.
A follow-up postnatal ultrasound should be performed 36–48 h after birth to avoid the transient neonatal dehydration.
Earlier postnatal ultrasound (24–48 h) is performed for those with severe PUJ obstruction.
Those with very large renal pelvis
Those with bilateral hydronephrosis
Those with solitary kidney
Those with PUJ obstruction and oligohydramnios
The most widely used grading system of the severity of hydronephrosis on ultrasonography after birth is SFU (Society for Fetal Urology) system, rather than the anteroposterior diameter of the renal pelvis.
The SFU grading system for hydronephrosis is as follows :
Grade 0:
No hydronephrosis, intact central renal complex seen on ultrasonography
Grade 1:
Only renal pelvis visualized, dilated pelvis on ultrasonography, no caliectasis
Grade 2:
Moderately dilated renal pelvis and a few calyces
Grade 3:
Hydronephrosis with nearly all calyces seen, large renal pelvis without parenchymal thinning
Grade 4:
Severe dilatation of renal pelvis and calyces with accompanying parenchymal atrophy or thinning
Approximately 20 % of antenatally diagnosed hydronephroses are not found on postnatal ultrasound.
PUJ obstruction is known to be associated with other types of congenital abnormality. This is seen in almost 50 % of patients.
PUJ obstruction is bilateral in about 10 % of patients (Figs. 3.16, 3.17 and 3.18).
Figs. 3.16, 3.17, and 3.18
Abdominal CT-scan and intravenous urography showing bilateral hydronephrosis secondary to PUJ obstruction
About 10 % of patients with PUJ obstruction have ipsilateral vesicoureteral reflux and to detect this, a voiding cystourethrogram should be part of the work-up of these patients.
There are also reports of coexisting PUJ obstruction and uretero-vesical junction obstruction. In these cases, the uretero-vesical obstruction is usually mild and PUJ obstruction should be treated first.
Duplication anomalies usually cause PUJ obstruction at the lower poles and the possibility of vesicoureteral reflux should be rolled out.
Rarely, the PUJ may be so severe leading to massive dilation of the renal collecting system and these patients may present with a palpable flank mass. This however is a rare and unusual presentation of PUJ at present.
PUJ obstruction is often associated with other congenital anomalies, including:
Anorectal malformations
Contralateral multicystic kidney
Congenital heart disease
VATER (vertebra, anus, trachea, esophageal, renal) syndrome
Esophageal atresia
The SFU Grading System for Hydronephrosis
Grade 0:
No hydronephrosis, intact central renal complex seen on ultrasonography
Grade 1:
Only renal pelvis visualized, dilated pelvis on ultrasonography, no caliectasis
Grade 2:
Moderately dilated renal pelvis and a few calyces
Grade 3:
Hydronephrosis with nearly all calyces seen, large renal pelvis without parenchymal thinning
Grade 4:
Severe dilatation of renal pelvis and calyces with accompanying parenchymal atrophy or thinning
3.6 Diagnosis and Investigations
Prenatal evaluation:
Prenatal ultrasound is widely used to diagnose fetal abnormalities.
Among these abnormalities is PUJ obstruction.
Prenatal ultrasound evaluation should include the followings:
Amniotic fluid volume to rule out oligohydramnios
Bladder volume
Kidney size
Anteroposterior diameter of the renal pelvis
Other associated abnormalities
Functionally significant hydronephrosis can be determined when:
The anteroposterior diameter of the renal pelvis is more than 10 mm.
The ratio of the renal pelvis to the anteroposterior kidney size is more than 0.3.
There is evidence of caliectasis after 24 weeks of gestation.
Patients with PUJ obstruction diagnosed by prenatal ultrasound should have a postnatal ultrasound. The timing of ultrasound is variable and depends on the severity of the PUJ obstruction.
In general, however, ultrasound examination should be avoided in the first 2 days after birth, because hydronephrosis may not be detected because of extracellular fluid shifts that will underestimate the degree of hydronephrosis.
Therefore, in unilateral disease, ultrasonography should be performed at least after 48 h of life.
These patients should also be placed on prophylactic antibiotics (amoxicillin 15 mg/kg) to prevent urinary tract infections.
Other investigations include:
Complete blood count
Urine analysis and culture
Serum electrolytes, BUN and creatinine
Plain abdominal radiograph
Abdominal ultrasound
Abdominal CT-scan
Abdominal MRI
A nuclear renal scan can
Intravenous urography
Voiding cystourethrography
Percutaneous nephrostography
Cystoscopy and retrograde pyelography
A Whitaker antegrade pressure-flow study
Serum electrolytes, BUN and creatinine are important to measure renal function especially in those with bilateral disease.
Urine analysis and culture are important to roll out associated urinary tract infection especially in asymptomatic patients.
Abdominal radiograph (Fig. 3.19):
Fig. 3.19
Abdominal radiograph showing a soft tissue density on the left side in a child with severe left PUJ obstruction
A plain abdominal x-ray may show a soft tissue density secondary to a hydronephrotic kidney.
A plain abdominal x-ray may also show radiopaque stones complicating PUJ obstruction.
Abdominal ultrasound (Figs. 3.20 and 3.21):
Figs. 3.20 and 3.21
Andominal ultrasound showing severe hydronephrosis secndary to PUJ obstruction
Renal ultrasound will show a dilated renal pelvis with a collapsed non-dilated ureter.Related posts:
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