Pediatric Surgery, AlSadik Hospital, Qatif, Saudi Arabia
The word “hydro” represents “water” and “nephro” represents “kidney”.
Hydronephrosis means “water inside the kidney”.
Hydronephrosis is defined as distension and dilation of the renal pelvis and calyces (Figs. 2.1 and 2.2).
Figs. 2.1 and 2.2
Intravenous urogram and a micturating cystourethrogram showing bilateral hydronephrosis and unilateral hydroureteronephrosis
Hydroureteronephrosis refers to distention of both the ureter and the renal pelvis and calices.
Hydronephrosis is usually caused by obstruction of the free flow of urine from the kidney.
Hydroureteronephrosis is usually caused by obstruction at the uretrovesical junction or below.
The signs and symptoms of hydronephrosis depend upon:
Whether the obstruction is acute or chronic
Whether the obstruction is partial or complete
Whether the obstruction is unilateral or bilateral
Hydronephrosis that occurs acutely with sudden onset can cause intense pain in the flanks (Dietl’s crisis).
If symptoms occur they can include:
Back, flank or lower abdominal pain
Nausea and vomiting
Burning during micturition
Febrile urinary tract infections
Hydronephrosis should be graded accurately in order to make good clinical decisions concerning the management and follow-up.
There are currently two methods to grade the degree of hydronephrosis:
The simple classification system of “mild, moderate, and severe” is less accurate.
The Society for Fetal Urology (SFU) has developed a more accurate numerical grading system for hydronephrosis.
The causes of hydronephrosis can be congenital or acquired.
It is important to understand that hydronephrosis does not always mean there is obstruction to the flow of urine from the kidney and hydronephrosis is a secondary effect of some other disease. Thus, the terms hydronephrosis and obstruction should not be used interchangeably.
With the widespread use of prenatal ultrasounds, antenatal hydronephrosis is currently the most common diagnosed prenatal condition.
Hydronephrosis can be caused by obstruction anywhere along the upper or lower urinary tract.
Obstruction that occurs anywhere along the upper urinary tract will lead to increased pressure within the kidney.
Obstruction occurring in the lower urinary tract can also cause this increased pressure through efflux of urine into the kidney.
This would eventually lead to:
Urinary tract infection
Loss of renal function
Neonatal hydronephrosis can be caused by several abnormalities. These commonly include (Figs. 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, and 2.9):
Figs. 2.3 and 2.4
Intravenous urography and micturating cystourethrogram showing pelviureteric junction obstruction and bilateral vesicoureteric reflux
Figs. 2.5 and 2.6
A micturating cystourethrogrma showing severe vesicoureteric reflux in a patient with a duplex system. An intravenous urogram showing a negaureter with hydroureteronephrosis is seen in the second picture. In patients with megaureter, there is no anatomical obstruction at the uretrovesical junction and micturating cystourethrogram doe not show vesico ureteric reflux
Figs. 2.7, 2.8, and 2.9
An intravenous urogram showing hydrouretronephrosis secondary to obstruction at the uretrovesical junction. Note the ureter tappering at the lower part. This was confirmed intraoperatively in the second two intraoperative picrures. Note the dilated ureter above the site of obstruction. This was treated by resection of the stenotic part and reimplantation of the ureter
Ureteropelvic junction obstruction
Ureterovesical junction obstruction
Ureterovesical junction obstruction and megaureter are fairly uncommon and, therefore, pediatric patients who have hydronephrosis and a normal voiding cystourethrogram are presumed to have ureteropelvic junction obstruction.
Prenatally diagnosed hydronephrosis:
Approximately 50 % are transient and resolve by the time the infant is born.
In 15 %, the hydronephrosis persists (non-refluxing, non-obstructing hydronephrosis) but spontaneously regress by age 3 years.
In the remaining 35 %, a pathological cause can be identified.
Extensive use of prenatal ultrasound has led to an increased rate of diagnosis of neonatal hydronephrosis, of which ureteropelvic junction obstruction is the most frequent cause.
Ureteropelvic junction obstruction occurs in approximately 1 in every 2,000 live births and accounts for approximately half of the cases of prenatal hydronephrosis.
In most cases, neonatal hydronephrosis secondary to ureteropelvic junction obstruction gradually resolves without surgical intervention.
There is a strong correlation between the Society for Fetal Urology (SFU) grade of hydronephrosis and the likelihood of spontaneous resolution:
Grade I resolves in approximately 50 % of patients
Grades II resolves in approximately 36 % of patients
Grade III resolves in approximately 16 % of patients
Grade IV resolves in approximately 3 % of patients
The initial severity of the hydronephrosis at the time of antenatal diagnosis and the presence of the hydronephrosis at birth were the only two factors that predicted hydronephrosis failure to resolve.
Hydronephrosis that was mild to mild-to-moderate in severity resolved in 71 % of patients, compared to 28 % of children with moderate to severe hydronephrosis. This supports the claim that the severity of hydronephrosis predicts failure of the lesion to resolve.
Hydronephrosis can result from anatomic or functional causes that interrupt the flow of urine (Figs. 2.10 and 2.11).
Figs. 2.10 and 2.11
Two micturating cystourethrograms showing hydrouretronephrosis with dilated urinary bladder secondary to posterior urethral valve. Note the tortuous dilated ureter
This interruption can occur anywhere along the urinary tract from the kidneys to the urethral meatus.
Gross changes within the urinary tract depend on:
The duration of obstruction
The degree of obstruction
The level of obstruction
Within the intrarenal collecting system, the degree of dilation is limited by surrounding renal parenchyma.
This is in contrast to the extrarenal components which can dilate to the point of tortuosity.
Hydronephrosis can reasonably be viewed as a beneficial compensatory mechanism that actually protects the kidney against high intrapelvic pressures and further renal damage.
The extent and persistence of these functional insults are directly related to the duration and severity of the obstruction.
Brief disruptions lead to reversible functional disturbances with little associated anatomic changes.
More chronic disruptions lead to profound tubular atrophy and permanent nephron loss.
The rise in ureteral or renal pelvic pressure leads to marked changes in glomerular filtration, tubular function, and renal blood flow.
The glomerular filtration rate (GFR) declines significantly within hours following acute obstruction. This significant decline of GFR can persist for weeks after relief of obstruction.
In addition, renal tubular ability to transport sodium, potassium, to concentrate and to dilute the urine is severely impaired.
Increased ureteral pressure also results in pyelovenous and pyelolymphatic backflow.
Acute hydronephrosis when corrected, usually allows full recovery of renal function.
It can be associated with little anatomic disturbance to renal parenchyma.
In chronic hydronephrosis, the loss of function is usually irreversible even with correction of the obstruction.
It may be associated with compression of the papillae, thinning of the renal parenchyma around the calyces, and coalescence of the septa between calyces.
Eventually, cortical atrophy progresses to the point at which only a thin rim of parenchyma is present (Figs. 2.12, 2.13, and 2.14).
Intraoperative photograph showing an atrophic kidney with dilated refluxing duplex system. Note the markedly dilated duplex ureter
Figs. 2.13 and 2.14
Intraoperative photographs showing atrophic kidneys secondary to severe reflux and hydroureters
Microscopic changes consist of dilation of the tubular lumen and flattening of the tubular epithelium. Fibrotic changes and increased collagen deposition are observed in the peritubular interstitial tissue.
Long-standing hydronephrosis may be associated with obstructive nephropathy and renal failure.
Patients with complete or severe partial bilateral obstruction also may develop acute or chronic renal failure.
Urinary stasis as a result of obstruction may be complicated by:
Hypertension is occasionally induced by renal obstruction.
The mechanism responsible for the elevation in blood pressure varies with the duration and type of obstruction.
Acute, unilateral obstruction can cause hypertension via activation of the renin-angiotensin system.
The elevation in blood pressure is probably volume mediated as renin secretion is usually normal in patients with bilateral urinary tract obstruction or obstruction of a solitary functioning kidney. The elevation in blood pressure resolves with the diuresis following correction of the obstruction.
The plasma renin activity is also typically normal in chronic unilateral obstruction, and the elevation in blood pressure is unrelated to the renal disease.
The pathophysiological changes of hydronephrosis depends on several factors which can be summarized as follows:
Persistent hydronephrosis will lead to the following changes:
Dilatation of the renal pelvis and the intrarenal collecting system.
The degree of dilatation is limited by surrounding renal parenchyma.
This will lead to compression of the papillae, thinning of the parenchyma around the calyces, and coalescence of the septa between calyces.
Eventually, cortical atrophy progresses to the point at which only a thin rim of parenchyma is present.
Fibrotic changes and increased collagen deposition are also observed in the peritubular interstitium.
The extrarenal dilatation can progress leading to ureteral dilatation to the point of tortuosity.
Urinary stasis in these patients may result in complications including:
Loss of renal function
Longstanding hydronephrosis may be associated with obstructive nephropathy, hypertension and renal failure.
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2.3 Etiology of Hydronephrosis
The etiology and presentation of hydronephrosis and/or hydroureter in adults differ from that in neonates and children (Figs. 2.15, 2.16, 2.17, 2.18, 2.19, 2.20, 2.21, 2.22, 2.23, 2.24, 2.25, 2.26, 2.27, 2.28, 2.29, 2.30, 2.31, 2.32, 2.33, and 2.34).
Figs. 2.15 and 2.16
Intravenous urography showing bilateral hydroureters and hydronehrosis secondary to exteral compression by a distended vagina and uterus (hydrometrocolpos) secondary to vaginal atresia. This will resolve once the vaginal atresia is treated
Figs. 2.17, 2.18, and 2.19
MRI showing bilateral hydronephrosis and distended vagina secondary to vaginal atresia
Figs. 2.20 and 2.21
Inra-operative photographs showing hydrometrocolpos secondary to vaginal atresia. The distended vagina and uterus will lead to compression on the ureters leading to hydroureteronephrosis. Drainage of the hydrometrocolpos will lead to relief of the obstruction and resolution of the hydroureteronephrosis
Figs. 2.22 and 2.23
Plain abdominal x-ray and IVU showing a staghorn stone in a child causing hydronephrosis. The stone took the shape of the renal pelvis and cayces. Note the stone is causing obstruction and hydronephrosis on the IVU
Figs. 2.24, 2.25, and 2.26
Intravenous urogram and voiding cystourethrogrms showing unilateral hydroureteronephrosis secondary to uretrovesical obstruction and posterior urethral valve
Figs. 2.27 and 2.28
A voiding cystourethrogram showing urethral stricture causing vesicoureteral reflux with hydroureter and hydronephrosis
Figs. 2.29, 2.30, 2.31, and 2.32
Abdominal and pelvic ultrasound and CT-scan showing right and left uretrocele with hydroureter and hydronephrosis
Figs. 2.33 and 2.34
A cystogram showing an uretrocele and intraoperative photograph showing a large ureterocel causing obstruction and marked hydroureter and atrophic dysplastic kidney
The causes of hydronephrosis with or without hydroureter depends on:
The site of obstruction
Whether it is unilateral or bilateral
Whether it is intrinsic, extrinsic or functional.
The following are the main causes of hydronephrosis in infants and children:
Pelvi-ureteric junction obstruction
Ureterovesical junction obstruction
Ureteral folds and valves
Benign fibroepithelial polyps
Hydrocolpos and hydrometrocolpos
Duplicated renal collecting systems
Multi cystic dysplastic kidney
Retroperitoneal lymphoma and sarcoma
Renal, bladder and ureteric calculi
Posterior urethral valve
Posterior urethral valves
Phimosis and meatal stenosis
Multi cystic dysplastic kidney (MCDK) (Figs. 2.35, 2.36, and 2.37):
CT-scan showing multicystic dysplastic kidney
Figs. 2.36 and 2.37
Clinical photographs showing resected multicystic dysplastic kidneys
This will show several round, well defined, cystic structures within the kidney that often look just like severe hydronephrosis.
These abnormally developed kidneys are generally found early in pregnancy through antenatal ultrasounds.
The true diagnosis can be confirmed postnatally by the following tests:
A post-natal ultrasound
A voiding cystourethrogram
A nuclear renal scan
The renal scan confirms that the kidney has no function.
MCDKs have no function and will involute (shrink up) over time.
Rarely, these multi cystic dysplastic kidneys needs to be removed for the following reasons:
Very large multi cystic dysplastic kidney
If they fail to involute
If they rupture
If they develop unmanageable high blood pressure
If they are complicated by severe infection
There are several congenital and acquired conditions that can lead to hydronephrosis in infants and children.
PUJ (Pelvi-Ureteric Junction) obstruction
Posterior urethral valve
Uretro-vesical junction (UVJ) obstruction
Abnormal polar vessels
Severe meatal stenosis
Kidney and ureteric stones
In children and in neonates, the relative frequency of the causes of antenatal hydronephrosis has been determined to be as follows: