Hydronephrosis and Hydroureter

Hydronephrosis can result from anatomic or functional processes interrupting the flow of urine. This interruption can occur anywhere along the urinary tract from the kidneys to the urethral meatus. The rise in ureteral 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, and protons and concentrate and to dilute the urine is severely impaired.

The extent and persistence of these functional insults is directly related to the duration and extent of the obstruction. Brief disruptions are limited to reversible functional disturbance with little associated anatomic changes. More chronic disruptions lead to profound tubular atrophy and permanent nephron loss.

Increased ureteral pressure also results in pyelovenous and pyelolymphatic backflow. Gross changes within the urinary tract similarly depend on the duration, degree, and level of obstruction. Within the intrarenal collecting system, the degree of dilation is limited by surrounding renal parenchyma. However, the extrarenal components can dilate to the point of tortuosity.

To distinguish acute and chronic hydronephrosis, one may consider acute as hydronephrosis that, when corrected, allows full recovery of renal function. Conversely, in chronic hydronephrosis the loss of function is irreversible even with correction of the obstruction. Early experiments with dogs showed that if acute unilateral obstruction is corrected within 2 weeks, full recovery of renal function is possible. However, after 6 weeks of obstruction, function is irreversibly lost.

Grossly, an acutely hydronephrotic system can be associated with little anatomic disturbance to renal parenchyma. On the other hand, a chronically dilated system may be associated with 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. 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 interstitium.

A multitude of causes exist for hydronephrosis and hydroureter. Classification can be made according to the level within the urinary tract and whether the etiology is intrinsic, extrinsic, or functional.

Ureter

Intrinsic ureter-level causes can be as follows:

• Ureteropelvic junction stricture
• Ureterovesical junction obstruction
• Papillary necrosis
• Ureteral folds
• Ureteral valves
• Ureterovesical reflux
• Ureteral stricture (iatrogenic)
• Blood clot
• Benign fibroepithelial polyps
• Ureteral tumor
• Fungus ball
• Ureteral calculus
• Ureterocele
• Endometriosis
• Tuberculosis
• Retrocaval ureter

Functional ureter-level causes can be as follows:

• Gram-negative infection
• Neurogenic bladder

Extrinsic ureter-level causes can be as follows:

• Retroperitoneal lymphoma
• Retroperitoneal sarcoma
• Cervical cancer
• Prostate cancer
• Retroperitoneal fibrosis
• Aortic aneurysm
• Inflammatory bowel disease
• Ovarian vein syndrome
• Retrocaval ureter
• Uterine prolapse
• Pregnancy
• Iatrogenic ureteral ligation
• Ovarian cysts
• Diverticulitis
• Tuboovarian abscess
• Retroperitoneal hemorrhage
• Lymphocele
• Pelvic lipomatosis
• Radiation therapy
• Urinoma

Bladder

Intrinsic bladder-level causes can be as follows:

• Bladder carcinoma
• Bladder calculi
• Bladder neck contracture
• Cystocele
• Primary bladder neck hypertrophy
• Bladder diverticula

Functional bladder-level causes can be as follows:

• Neurogenic bladder
• Vesicoureteral reflux

Extrinsic bladder-level causes can include pelvic lipomatosis.

Urethra

Intrinsic urethra-level causes can be as follows:

• Urethral stricture
• Urethral valves
• Urethral diverticula
• Urethral atresia
• Labial fusion
• Hypospadias and epispadias

Extrinsic urethra-level causes can be as follows:

• Benign prostatic hyperplasia (BPH)
• Prostate cancer
• Urethral and Penile cancer
• Phimosis

Frequency

United States

An autopsy series of 59,064 subjects ranging in age from neonates to geriatric persons reported hydronephrosis in 3.1%.[6] In this series, differences based on sex did not become apparent until age 20 years. At age 20-60 years, hydronephrosis was more common in women, possibly because of pregnancy and gynecologic malignancy. In men, prostatic diseases were indicated as the cause of the rise in prevalence after age 60 years. Autopsy studies also indicate that hydronephrosis is present in 2-2.5% of children.[6] The prevalence is slightly higher in boys, most of whom in the study were younger than 1 year.

These occurrence rates likely underestimate the prevalence because conditions such as temporary obstruction due to prior pregnancy or calculi were not included.

In a study that included 112 patients who underwent percutaneous nephrolithotomy, renal ultrasonography performed 4 - 6 weeks after stent removal, clinically silent hydronephrosis was identified in 16%. The hydronephrosis resolved spontaneously in 50% of cases, with a mean time to resolution of 6.3 months.[7]

Sex

In women, gynecologic cancers and pregnancy are common causes. As such, among younger patients (aged 20-60 y), the frequency of hydronephrosis is higher in women than in men.

In men, obstruction secondary to prostatic hypertrophy and prostate cancer are the major causes of hydronephrosis. Consequently, among older patients (>60 y), the frequency of hydronephrosis is higher in men than in women. 

Age

In young adults, calculi are the most common causes of hydroureter and hydronephrosis.

In children and in neonates, the relative frequency of the causes of antenatal hydronephrosis has been determined to be as follows:

• Transient - 48%
• Physiologic -15%
• Ureteropelvic junction obstruction - 11%
• Vesicoureteral reflux - 9%
• Megaureter - 4%
• Multicystic dysplastic kidney - 2%
• Ureterocele - 2%
• Posterior urethral valves - 1%

Long-standing hydronephrosis may be associated with obstructive nephropathy and renal failure. Patients with complete or severe partial bilateral obstruction also may develop acute kidney injury or chronic kidney disease. In the latter setting, the patient is often asymptomatic and the urinalysis results may be relatively normal or reveal only a few white or red blood cells.[8]  Thus, urinary tract obstruction should be considered in all patients with otherwise unexplained renal insufficiency. The history may be helpful in some cases, possibly revealing symptoms of prostatic enlargement or prior malignancy or renal calculi.

Urinary stasis may result in infection, renal scarring, calculus formation, and sepsis.

Hypertension is occasionally induced by obstruction. The mechanism responsible for the elevation in blood pressure varies with the duration and type of obstruction. What remains unclear, however, is why the factors described below result in hypertension in only a minority of obstructed patients:

Acute, unilateral obstruction can cause hypertension via activation of the renin-angiotensin system; renal vein renin studies lateralize the increase in renin secretion to the obstructed kidney, a finding similar to that in unilateral renal artery stenosis.[9]

Renin secretion is usually normal in patients with bilateral urinary tract obstruction or obstruction of a solitary functioning kidney.[9]  In this condition, renal failure leading to volume expansion is typically present; the elevation in blood pressure is probably volume mediated and resolves with the diuresis following correction of the obstruction.

The plasma renin activity is also typically normal in chronic unilateral obstruction, and the presence of the contralateral healthy kidney prevents both renal failure and fluid retention.[9]  Furthermore, relief of the obstruction may not correct the hypertension. These observations suggest that the kidney may have incurred some permanent damage and that the elevation in blood pressure is unrelated to the renal disease.

Postobstructive diuresis refers to polyuria that occurs after relief of obstruction. Patients with edema, congestive heart failure, hypertension, weight gain, and azotemia are most likely to exhibit this condition. It is more common in patients with chronic obstruction. Postobstructive diuresis is usually clinically significant only in patients whose obstruction involves both kidneys or a unilateral obstruction of a solitary functioning kidney.

Adult hydronephrosis and hydroureter

Symptoms vary depending on whether the hydronephrosis is acute or chronic.

With acute obstruction, pain is frequently present, due to distention of the bladder, collecting system, or renal capsule. Pain is typically minimal or absent with partial or slowly developing obstruction (as with congenital ureteropelvic junction [UPJ] obstruction or a pelvic tumor). It is not uncommon, for example, to see an adult who is noted to have hydronephrosis due to previously unsuspected UPJ obstruction.

In comparison, relatively severe pain (renal or ureteral colic) may be seen with acute complete obstruction (as with a ureteral calculus) or when acute dilatation occurs after a fluid load that increases the urine output to a level greater than the flow rate through the area of obstruction. An example of the latter problem occurs after beer drinking in a college student with previously asymptomatic and unsuspected UPJ obstruction.

The site of obstruction determines the location of pain. Upper ureteral or renal pelvic lesions lead to flank pain or tenderness, whereas lower ureteral obstruction causes pain that may radiate to the ipsilateral testicle or labia.

With regard to renal insufficiency, patients with complete or severe partial bilateral obstruction also may develop acute or chronic renal failure. In the latter setting, the patient is often asymptomatic and the urinalysis results may be relatively normal or reveal only a few white or red blood cells.[3]

Anuria may be a presenting symptom of the patient. Although the urine volume could be reduced in any form of renal disease, anuria is most often seen in 2 conditions: complete bilateral urinary tract obstruction and shock. Other less common causes of anuria are hemolytic-uremic syndrome, renal cortical necrosis, bilateral renal arterial obstruction, and crescentic or rapidly progressive glomerulonephritis, particularly anti–glomerular basement membrane (GBM) antibody disease. Bilateral symmetrical hydronephrosis usually suggests a cause related to the bladder, such as retention, prostatic blockage, or severe bladder prolapse.

Considerations include the following:

• A history of hematuria may herald a stone or malignancy anywhere in the urinary tract
• A history of fever or diabetes adds urgency to the evaluation and treatment
• Hydronephrosis in a patient with a solitary kidney is an emergent situation
• Hydronephrosis may develop silently, without symptoms, as the result of advanced pelvic malignancy or severe urinary retention from bladder outlet obstruction.

Pediatric hydronephrosis and hydroureter

Fetal hydronephrosis is a readily diagnosed finding on antenatal ultrasound examination and can be detected as early as the 12th to 14th week of gestation.[10]

Although renal pelvic dilatation is a transient, physiologic state in most cases, urinary tract obstruction and vesicoureteral reflux (VUR) are also causal. Most cases of antenatal hydronephrosis are not clinically significant and can lead to unnecessary testing of the newborn baby and anxiety for patients and healthcare providers.

Physical findings include the following:

• With severe hydronephrosis, the kidney may be palpable.
• With bilateral hydronephrosis, lower extremity edema may occur. Costovertebral angle tenderness on the affected side is common.
• A palpably distended bladder adds evidence of lower  urinary tract obstruction.

A digital rectal examination should be performed to assess sphincter tone and to look for hypertrophy, nodules, or induration of the prostate.

In children, the physical examination, especially in a newborn, can help detect abnormalities that suggest genitourinary abnormalities associated with antenatal hydronephrosis. These include the following:

• The presence of an abdominal mass could represent an enlarged kidney due to obstructive uropathy or multicystic dysplastic kidney (MCDK).
• A palpable bladder in a male infant, especially after voiding, may suggest posterior urethral valves.
• A male infant with prune belly syndrome will have deficient abdominal wall musculature and undescended testes. The presence of associated anomalies should be noted.
• The presence of outer ear abnormalities is associated with an increased risk of congenital anomalies of the kidney and urinary tract (CAKUT).
• A single umbilical artery is associated with an increased risk of CAKUT, particularly VUR.

Urinalysis is used to assess for signs of infection. Pyuria suggests the presence of infection. Microscopic hematuria may indicate the presence of a stone or tumor.

Complete blood cell count may reveal leukocytosis, which may indicate acute infection.

Serum chemistry studies can reveal an elevation of blood urea nitrogen (BUN) and creatinine levels, which may be the result of bilateral hydronephrosis and hydroureter. In addition, hyperkalemia can be a life-threatening condition.

Imaging in adults

Early diagnosis of urinary tract obstruction is important because most cases can be corrected and a delay in therapy can lead to irreversible renal injury.

Bladder catheterization should be performed initially if there is reason to suspect that bladder neck obstruction leading to acute or chronic urinary retention may be present. Possible clues to this diagnosis include suprapubic pain, a palpable bladder, or unexplained renal failure in an older man.

Radiologic tests are generally used to exclude obstruction at the level of the ureters or above by detecting dilatation of the collecting system. It is important to remember, therefore, that obstruction can occur without dilatation in the following three settings:

• Within the first 1-3 days, when the collecting system is relatively noncompliant and less likely to dilate: In this setting, unilateral obstruction can usually be diagnosed by duplex Doppler ultrasonography, which detects an increased resistive index (a reflection of increased renal vascular resistance) in the affected compared with the contralateral kidney.[11] This test is of no value with bilateral involvement because it cannot distinguish obstruction from intrinsic renal disease.

• When the collecting systems are encased by retroperitoneal tumor or fibrosis: In this setting, hydronephrosis may be present in the absence of ureteral dilatation. Retroperitoneal fibrosis can occur in a number of settings, including retroperitoneal fibrosis (most commonly idiopathic or associated with beta-blocker or methysergide use, malignancy, or a connective-tissue disorder) and with the fibrotic reaction that surrounds a renal transplant.[12] Thus, the diagnosis of renal insufficiency due to asymptomatic obstruction in a transplanted kidney may be made based on renal biopsy findings, which show diffuse tubular dilatation, rather than the signs of rejection or cyclosporine nephrotoxicity.

• When the obstruction is mild, a setting in which renal function is not usually impaired

Renal ultrasonography is the test of choice to exclude urinary tract obstruction, avoiding the potential allergic and toxic complications of radiocontrast media.[13] It can, in the majority of affected patients, help diagnose hydronephrosis and establish its cause; it can also detect other causes of renal disease such as polycystic kidney disease.

Although ultrasound can accurately identify hydronephrosis, it is less sensitive than computed tomography (CT) for detecting stones in the ureters.   In one study, hydronephrosis on ultrasound had a positive predictive value of 0.77 for the presence of a ureteral stone and a negative predictive value of 0.71 for the absence of a ureteral stone.[14]  

Indications for CT scanning include the following:

• Ultrasonography results are equivocal
• The kidneys cannot be well visualized
• The cause of the obstruction cannot be identified

The combination of a plain film of the abdomen (including tomographic cuts to detect radiopaque calculi), ultrasonography, and, if necessary, CT scanning is adequate for diagnostic purposes in over 90% of cases.[15] It should be noted, however, that the false-positive rate for ultrasonography may be as high as 25% if only minimal criteria (any visualization of the collecting systems) are used to diagnose obstruction.

The advantages of intravenous pyelography (IVP) in relation to ultrasonography are that IVP has a very low false-positive rate, it can identify the site of obstruction, and it can help detect associated conditions such as papillary necrosis or calyceal blunting from previous infection.[15] Disadvantages are that IVP is more cumbersome to perform and requires the administration of a radiocontrast agent. On balance, IVP can be used to screen for urinary tract obstruction in the following settings:

• In patients with staghorn calculi or multiple renal or parapelvic cysts, since hydronephrosis is usually not distinguishable from cysts or stones by ultrasonography or CT

• When CT scanning cannot identify the level of obstruction

• With suspected acute obstruction due to kidney stones (or less frequently, to other problems, such as a sloughed papilla or blood clot): Dilatation of the collecting system may not be seen at this time, but the presence and location of the obstructing stone can be identified

Diffusion-weighted magnetic resonance imaging (MRI) may allow noninvasive detection of changes in renal perfusion and diffusion that occur during acute ureteral obstruction.[16] The advantage of this technique is that it does not require the use of contrast agents. However, the clinical utility of diffusion-weighted MRI has not been adequately tested.

Hydronephrosis without apparent obstruction or with asymptomatic obstruction

In some cases, one of the above radiologic tests demonstrates hydronephrosis without evidence of obstruction. This is a normal finding in pregnant women. Megaureter due to previous marked vesicoureteral reflux or a dilated but nonobstructed extrarenal pelvis is the most common example of this problem. These patients are often being evaluated for back or flank pain, and the following two questions need to be answered:

• Is obstruction present?
• Is the obstruction responsible for the pain?

In this setting, 3 different tests have been used: diuretic renography, IVP (less often), and perfusion pressure flow studies.[3]

Diuretic renography involves the administration of a loop diuretic (eg, 0.5 mg/kg of furosemide) prior to radionuclide renal scanning or during IVP, while the latter involves percutaneous insertion of a catheter into the dilated renal pelvis, followed by fluid perfusion into the pelvis at a rate of 10 mL/min. The marked increase in urine flow should, if obstruction is present, slow the rate of washout of the radioisotope during renal scanning, further increase the size of the collecting system on IVP, or elevate the renal pelvic pressure to above 22 mm Hg during a perfusion study. Furthermore, any of these procedures may precipitate pain similar to the patient's initial complaint.

Noninvasive diuretic renography is generally preferred. However, optimal interpretation of any of these test results is uncertain, because both false-positive and false-negative results may be seen. Nevertheless, the following general recommendations have been made:

• Surgical correction should be considered in a patient with pain and positive diuretic renography findings.

• No therapy is necessary in an asymptomatic patient with positive diuretic renography findings but normal renal function. These patients often are adults and have therefore had the partial obstruction for many years without apparent damage to the kidney. Hydronephrosis may first be noted after a radiologic study is performed for some other reason, or, as noted above, obstruction may be suspected when pain is induced after a period of high fluid intake leads to a diuresis that exceeds the rate at which urine can flow through the obstructed area. Similarly, the decreased washout observed on renography occurs only at a urine flow rate much higher than the patient is likely to achieve on his or her own. Periodic monitoring of renal function and renal parenchymal size (by ultrasonography) is indicated in these patients to exclude progressive renal injury.

• No therapy is indicated in an asymptomatic patient with negative renography findings. Long-term follow-up has demonstrated stable renal function in most of these patients.

• A perfusion pressure flow study should be performed in a symptomatic patient with negative or equivocal diuretic renography findings. Some nonrenal cause for the pain is probably present if the perfusion study is negative. On the other hand, a positive study is suggestive of obstruction and the need for surgical correction.

• A perfusion pressure flow study may also be performed in patients with hydronephrosis and poor renal function. The diuretic renogram may be falsely negative in this setting, because the diuretic may not sufficiently raise the urine flow.

In general, approximately 50% of patients with positive diuretic renography findings eventually require surgery, either for pain or progressive parenchymal loss.[17]

Imaging in children

The following grading systems have been developed for evaluating hydronephrosis severity in infants[18] :

• Anterior-posterior (AP) diameter of renal pelvis
• Society for Fetal Urology (SFU)
• Radiology
• Urinary Tract Dilatation (UTD)
• Onen

The Onen grading system applies to both prenatal and postnatal ureteropelvic junction–type hydronephrosis and includes two categories of findings: dilation of the pelvicalyceal system and, most important, the quality of the renal parenchyma (thickness and appearance). AP diameter is not important.[18]

The Onen system has four grades. Grade 1 criterion is renal pelvic dilatation. Grade 2 criteria are as follows:

• Pelvis and caliceal dilatation
• Renal parenchyma (medulla and cortex) are normal (> 7 mm)

Grade 3 criteria are as follows:

• Pelvis and caliceal dilatation
• Medulla is short and thin
• Cortex is normal
• Total parenchymal thickness 2-5 mm second trimester, 2.5-6 mm third trimester, 3-7 mm postnatal
• Corticomedullary differentiation is normal

Grade 4 criteria are as follows:

• Pelvis and caliceal dilatation
• No medulla is present (total loss)
• Cortex is thin (second trimester, < 2 mm; third trimester, < 2.5 mm; postnatal, < 3 mm)
• No corticomedullary differentiation is visible
• Recesses between calyxes are significantly short and thin

Detection of antenatal hydronephrosis by ultrasound usually occurs in the second trimester. In this setting, hydronephrosis is defined as renal pelvic dilation (RPD) of 4 mm or more. Mild hydronephrosis (RPD of 4-10 mm or SFU grade 1 or 2) can be associated with Down syndrome or other chromosome anomalies. More severe dilatation increases the risk of renal and/or urinary tract disorders.

During the ultrasonography, the appearance of the fetal renal system can vary in both healthy fetuses without hydronephrosis and those with hydronephrosis. Therefore, this diagnosis should not be based on a single measurement.[19] An increase of maternal hydration can also increase the RPD in both healthy fetuses and those with hydronephrosis.[20]

If fetal hydronephrosis is detected, the following parameters need to be evaluated using ultrasonography, as they guide further need for evaluation and are helpful in determining the cause of hydronephrosis:

• Severity of hydronephrosis: The likelihood of a congenital kidney or urinary tract anomaly increases with the severity of RPD.

• Unilateral versus bilateral involvement: Bilateral involvement increases the risk of a significant renal abnormality and the risk of impaired postnatal renal function.

• Ureter: Dilatation of the ureter can be consistent with vesicoureteral reflux (VUR) or obstructive uropathy distal to the ureteropelvic junction.

Postnatal radiologic studies

Postnatal radiologic evaluation of a newborn with antenatal hydronephrosis begins with an ultrasonography examination. The timing of ultrasonography and the need for other studies depend on the severity of postnatal hydronephrosis and whether there is bilateral involvement or an affected solitary kidney.

Ultrasonography of kidneys and bladder should be performed in the postnatal period on affected infants. The timing of the study depends on the severity of the antenatal hydronephrosis. In general, examination should be avoided in the first 2 days after birth because hydronephrosis may not be detected because of extracellular fluid shifts that underestimate the degree of hydronephrosis. However, infants with bilateral hydronephrosis and those with a severe hydronephrotic solitary kidney require urgent evaluation on the first postnatal day because of the increased likelihood of significant disease and a possible need for early intervention. For unilateral hydronephrosis without antenatal bladder pathology, performing postnatal sonography 1-4 weeks after birth is recommended.

A voiding cystourethrography (VCUG) is performed to detect VUR and, in boys, to evaluate the posterior urethra. For this procedure, a urinary catheter is inserted into the bladder and contrast material is instilled. Fluoroscopic monitoring is performed while the bladder is filling and during voiding. Infants usually tolerate this procedure well. Although the duration of fluoroscopy is minimized, the gonads, especially the ovaries, are exposed to radiation.[21]

Diuretic renography is used to diagnose urinary tract obstruction in infants with persistent hydronephrosis and is usually ordered after a VCUG has demonstrated no vesicoureteral reflux.[22] It measures the drainage time from the renal pelvis and assesses total and individual kidney renal function. The test requires insertion of a bladder catheter to relieve any pressure that can be transmitted to the ureters and kidneys. Intravenous access is needed for hydration and the administration of the radioisotope and diuretic. The preferred radioisotope is technetium Tc 99m-mercaptoacetyltriglycine (Tc99mMAG3), which is taken up by the renal cortex, filtered across the glomerular basement membrane to the renal tubules, and excreted into the renal pelvis and urinary tract.[23]

Diuretic renography includes two phases. First, radioisotope is injected intravenously and renal parenchymal (cortical) uptake is measured during the first 2-3 minutes. The relative contribution of each kidney to overall renal function (called the split renal function) is assessed quantitatively and is useful as a baseline study. Subsequent studies can be compared to assess whether kidney function remains stable or has deteriorated, suggesting true obstruction.[24]

Second, at peak renal uptake, intravenous furosemide is administered and the excretion of isotope from the kidney is measured, referred to as the washout curve. This phase indicates the extent of obstruction, if present. In a healthy kidney, furosemide administration results in a prompt washout. In a dilated system, if washout occurs rapidly after diuretic administration (< 15 min), the system is not obstructed. If washout is delayed beyond 20 minutes, the pattern is consistent with obstructive uropathy. However, a delayed washout must be interpreted with caution.[25, 26]

In a series of 39 infants with antenatal unilateral hydronephrosis followed without surgery, diuretic renography indicated obstruction in 24 patients whose renal function never decreased and who thus did not have obstruction.[26] These results may be due, in part, to the normally low neonatal GFR that can be refractory to diuretic therapy. If washout is from 15-20 minutes, the study is indeterminate.

Gravity-assisted drainage imaging may assist in the assessment of pediatric hydronephrosis. Unlike customary diuretic renography, in which the patient remains supine, with gravity-assisted renography a single, static image is obtained after positioning the child in the upright position for 5 minutes to promote additional drainage of tracer from the collecting system. Notable improvement in drainage with this maneuver suggests that slowness in drainage is not due to urinary tract obstruction.[27]

Split renal function results are the most useful criteria to evaluate a decrease in renal function. In patients with unilateral hydronephrosis (which is the most common clinical scenario), if the normal nonhydronephrotic kidney and hydronephrotic kidney both have equal function, conservative management without surgery is a safe option. In a cohort of 831 cases of antenatal hydronephrosis, renal scanning performed in 229 newborns demonstrated that 16% of patients had a significant decrease in renal function of one kidney, defined as 35% or less differential renal function.[28] A decrease in differential renal function was associated with severe antenatal hydronephrosis (ie, renal pelvic diameter >10 mm at 20-24 wk gestation and >16 mm at 33 wk gestation).

Magnetic resonance urography (MRU) in children is becoming more commonly used in the diagnosis and management of congenital uropathies such as UPJ obstruction.[29, 30] MRU is especially useful in the management of obstructed kidneys that have rotation or ascent anomalies, or are solitary. MRU can more clearly define the anatomy and delineate the proper surgical approach (ie, retroperitoneal vs transperitoneal). Newer MRU technology may even define obstruction, eliminating the need for diuretic renal scanning.

The disadvantage of MRU is that the study often requires general anesthesia or heavy conscious sedation in children. Furthermore, the contrast agent gadolinium can only be used if renal function is normal (requiring a preprocedure serum creatinine test) because of reports of irreversible renal fibrosis in patients with renal insufficiency.

Antegrade or retrograde pyelography is usually used to relieve, rather than diagnose, urinary tract obstruction. However, these procedures can also be performed for diagnosis when the history is highly suggestive (eg, unexplained acute kidney injury in a patient with known pelvic malignancy), even though hydronephrosis may be absent (due to possible ureteral encasement) on ultrasonography and CT scanning.[15]

In fetuses with severe oligohydramnios and documented lung maturation, early delivery has been suggested. Although no data document improved renal outcome with early delivery, early delivery may be indicated to reduce the risk of other adverse outcomes from oligohydramnios, such as umbilical cord compression.

The role of medical treatment of hydronephrosis and hydroureter in adults is limited to pain control and treatment or prevention of infection. Most conditions require either minimally invasive or open surgical treatment. Two notable exceptions are (1) oral alkalinization therapy for uric acid stones and (2) steroid therapy for retroperitoneal fibrosis.

The management approach to infants with antenatal hydronephrosis is based on the confirmation of persistent postnatal hydronephrosis and the following two predictive factors:

• Bilateral involvement
• Severe hydronephrosis: Fetuses with a renal pelvic diameter greater than 15 mm during the third trimester are at the greatest risk for significant kidney disease

Bilateral hydronephrosis

Infants with severe bilateral antenatal hydronephrosis and/or bladder distension are at increased likelihood of having significant disease. These infants and those with a severe hydronephrotic solitary kidney should be evaluated initially by ultrasonography on the first postnatal day. Bilateral hydronephrosis suggests an obstructive process at the level of or distal to the bladder, such as ureterocele or posterior urethral valves (PUV) in a male infant, which can be associated with impaired renal function and ongoing renal injury.

If postnatal ultrasonography demonstrates persistent hydronephrosis, voiding cystourethrography (VCUG) should be performed. In male infants, the posterior urethra should be fully evaluated to detect possible PUVs.

Infants with mild or moderate hydronephrosis can be evaluated after 7 days of life.

Severe unilateral hydronephrosis

In newborns with severe antenatal unilateral hydronephrosis (renal pelvic diameter > 15 mm in the third trimester), ultrasonography should be performed after the infant returns to birth weight (after age 48 h and within the first 2 wk of life).

Moderate and mild unilateral hydronephrosis

In newborns with less severe antenatal unilateral hydronephrosis (renal pelvic diameter < 15 mm during third trimester), ultrasonography can be performed after age 7 days to see whether the hydronephrosis has persisted postnatally.

Moderate hydronephrosis resolves by age 18 months in most cases. This was illustrated by a prospective study of 282 infants (age 2 mo) with renal pelvic diameters between 10 and 15 mm, which resolved in 94% of patients by age 12-14 months (resolution was defined as renal pelvic diameter ≤5 mm on two consecutive ultrasounds). Of the 18 patients with persistent hydronephrosis, 14 had ureteropelvic junction (UPJ) obstruction and 4 had vesicoureteral reflux (VUR).[31]

Antibiotic prophylaxis

Higher rates of urinary tract infection (UTI) have been reported in children with prenatally diagnosed hydronephrosis compared with the general pediatric population.[32, 33] The risk of infection rises if there is an underlying urologic abnormality, such as VUR or obstructive uropathy, and is greater in girls than in boys.[34]

As a result, in infants with severe hydronephrosis who are at greater risk for an underlying urologic abnormality, antibiotic prophylaxis is started after delivery until the diagnosis of VUR or obstructive uropathy is excluded.

Antibiotic prophylaxis in children with mild or moderate hydronephrosis confirmed postnatally has not been studied prospectively. However, a prospective study of 237 children diagnosed with prenatal hydronephrosis found that those with ureteral diameter 7 mm or greater had three times the risk of UTI regardless of the presence of VUR and would likely benefit from continuous antibiotic prophylaxis. Conversely, patients with non-refluxing hydroureter less than 7 mm were not at increased risk of UTI.[35]  

In one retrospective study of 1514 with mild persistent hydronephrosis, the use of prophylactic antibiotics reduced the risk of febrile UTI in patients who had VUR.[36] Until further prospective studies are conducted, antibiotic prophylaxis should be considered until VCUG has been performed and either the diagnosis of VUR has been made or eliminated.

Antibiotic prophylaxis is not needed in infants with normal postnatal ultrasonography findings.[37]

Four retrospective studies have considered the role of antibiotic prophylaxis in infants with hydronephrosis. Zareba et al analyzed the risk factors for UTI in 376 infants with prenatal hydronephrosis and reported that infants with high-grade hydronephrosis, girls, and uncircumcised boys were at highest risk for UTI. Antibiotic prophylaxis did not decrease the risk in any of the groups studied.[38]

In a systematic review that included 3876 newborns with antenatal hydronephrosis, Braga et al found that infants with high-grade hydronephrosis receiving continuous antibiotic prophylaxis (CAP) had significantly lower UTI rates than those who did not receive an antibiotic regimen (14.6% vs 28.9%). However, the rates for infants with low-grade hydronephrosis were similar (2.2% vs. 2.8%). The researchers cautioned that the level of evidence of available data was moderate to low.[39]

Herz et al reviewed the records of 278 children maintained on CAP and 127 who were not and compared individual characteristics to determine risk factors for UTI. The presence of ureteral dilation, high-grade VUR, and ureterovesical junction obstruction were independent risk factors for development of UTI. CAP had a significant role in reducing UTI in children with the risk factors but was unnecessary otherwise.[40]

Varda et al studied the use of CAP during the interval between birth and initial neonatal imaging in 494 infants with a history of prenatal urinary tract dilation, and these authors concluded that routine CAP may be of limited benefit in most patients in this setting. The incidence of UTI prior to initial neonatal imaging was low, and was not significantly different in study patients who received CAP and those who did not. The ropensity score adjusted odds of developing UTI with CAP versus without was 0.93 (95% CI 0.10-8.32; P = 0.95).[41]

A systematic review from the European Association of Urology/European Society for Paediatric Urology Guidelines Panel found that most studies of CAP had low-to-moderate quality of evidence and high risk of bias. Consequently, the panel concluded that whether CAP is superior to observation in decreasing UTIs remains unproven. However, CAP may be warranted in uncircumcised boys, children with ureteral dilatation, and those with high-grade hydronephrosis, who may be more likely to develop UTI.[42]

The specific treatment of a patient with hydronephrosis and hydroureter depends, of course, on the etiology of the process. Several factors help determine the urgency with which treatment should be initiated. In general, any signs of infection within the obstructed system warrant urgent intervention because infection with hydronephrosis may progress rapidly to sepsis. A mildly elevated white blood cell count is often observed in patients with stones but does not necessarily mandate immediate action in the absence of other signs or symptoms of systemic infection. However, even a low-grade fever in a diabetic or immunosuppressed patient (ie, on steroid therapy) requires immediate treatment.

The potential for loss of renal function also adds to the urgency (eg, hydronephrosis or hydroureter bilaterally or in a solitary kidney). Finally, patient symptoms help determine the urgency with which treatment is initiated. For example, refractory pain in a patient with an obstructing ureteral calculus necessitates intervention, as does intractable nausea and vomiting.

Urethral catheterization is important to help rule out a lower tract cause for hydronephrosis and hydroureter. Difficulty in placing a Foley catheter may suggest urethral stricture or bladder neck contracture.

Urologists commonly use ureteral stent placement in cases of intrinsic and extrinsic causes of hydronephrosis. The procedure is usually performed in conjunction with cystoscopy and retrograde pyelography. Stents can bypass an obstruction and dilate the ureter for subsequent endoscopic treatment.

Urologists or interventional radiologists can place a percutaneous nephrostomy tube if ureteral stenting is not possible. Usually, ultrasonography is used first to locate the dilated collecting system. Using the Seldinger technique, a tube ranging from 8-12F can be placed. Nephrostomies are typically placed when a retrograde stent cannot be passed because of anatomic changes in the bladder or high-grade obstruction in the ureter. Because this procedure can be performed under local anesthesia, patients who are too hemodynamically unstable for general anesthesia may undergo percutaneous nephrostomy tube placement. In addition, nephrostomy tube placement may be performed with minimal use of radiation and may be useful in pregnant patients.

In a study of fluoroscopically guided percutaneous nephrostomy (PCN) placement in infants and young children (mean age 8.6 months; range, 1 day-75.5 mo), Hwang et al reported achieving complete decompression of hydronephrosis in 35 of 53 kidneys (66%) and incomplete decompression in 17 of 55 kidneys (32.1%). The authors concluded that PCN is a feasible and effective option for relieving urinary obstruction in these patients, and can serve as a bridging procedure to definitive corrective surgery.[43]

Advances in endoscopic and percutaneous instrumentation have decreased the role of open or laparoscopic surgery for hydronephrosis. Certain causes of hydronephrosis, mostly extrinsic, still require treatment with open surgery. Examples include retroperitoneal fibrosis, retroperitoneal tumors, and aortic aneurysms. Some stones that cannot be treated endoscopically or with extracorporeal shockwave lithotripsy require open removal. Although endoscopic management does play a role in low-grade low-stage ureteral tumors, these lesions also usually require open or laparoscopic surgical management.

Urine should be collected from the kidney when obstruction is relieved to allow identification and targeted treatment of any infection that may be present.

Fetal surgery

Although several prospective and retrospective studies have examined antenatal surgery in fetuses with sonographic findings consistent with lower urinary tract obstruction, no good evidence supports that this intervention improves renal outcome.[44] Although these procedures may increase the amount of amniotic fluid, thus potentially improving lung development and survival rate, the rate of chronic renal disease is high in survivors, necessitating renal replacement therapy in almost two thirds of the cases.

The benefit of vesicoamniotic shunting (VAS) proved inconclusive in the Percutaneous vesicoamniotic shunting in Lower Urinary Tract Obstruction (PLUTO) trial, which compared VAS with conservative nonsurgical management in 31 singleton fetuses younger than 28 weeks’ gestation with isolated bladder outflow obstruction. Although survival to 28 days and 1 year appeared to be higher with VAS than with conservative management, the PLUTO investigators could not prove benefit beyond reasonable doubt, and VAS was substantially more costly.[45]

Newborns in the PLUTO trial had a very low chance of surviving with normal renal function, regardless of whether they underwent VAS. Short-term and long-term morbidity in both trial groups was substantial, and complications of VAS resulted in pregnancy loss in some cases.[45]

Refer the patient to a urologist whenever hydronephrosis or hydroureter is newly diagnosed. Further consultations may be sought by the urologist, depending on the circumstances. For example, a nephrologist's input would be useful in cases of severe pathological postobstructive diuresis. In addition, an interventional radiologist would be needed for nephrostomy tube placement if urgent decompression is needed and ureteral stent placement is not possible. Patients with antenatal and postnatal hydronephrosis should be referred to a pediatric urologist for evaluation and management.

Monitor patients for postobstructive diuresis. This is a marked polyuria observed after relief of an obstructed system.

Patients who are most likely to experience postobstructive diuresis present with chronic obstruction, edema, congestive heart failure, hypertension, weight gain, and azotemia. Clinically significant postobstructive diuresis is usually seen only in the setting of prior bilateral obstruction or, similarly, a unilateral obstruction of a solitary functioning kidney.

This postobstructive diureses can lead to a marked diuresis with the wasting of sodium, potassium, phosphate, and the divalent cations. Management involves avoiding severe volume depletion, hypokalemia, hyponatremia, hypernatremia, and hypomagnesemia.

Volume or free-water replacement is appropriate only when the salt and water losses result in volume depletion or a disturbance of osmolality. In many cases, excessive volume or fluid replacement prolongs the diuresis and natriuresis. An appropriate starting fluid for replacement is 0.45% saline. During this period, vital signs, volume status, urine output, and serum and urine chemistry and osmolality should be monitored.

Postobstructive diuresis is usually self-limited. It usually lasts for several days to a week but may, in rare cases, persist for months.

Once the diagnosis is made and treatment is performed, follow-up imaging studies are necessary to assess for resolution of the hydronephrosis and hydroureter. Additionally, laboratory studies of renal function should be performed, to assess the recovery of renal function.

For ultrasonography follow-up, fetuses with mild hydronephrosis should have follow-up ultrasonography in the third trimester (32-34 wk gestation). The interval for follow-up examination and management is dictated by the initial findings and the amount of amniotic fluid. Those with resolution have a low risk of clinically significant pathology and do not need further antenatal or postnatal evaluation. Serial follow-up ultrasonography is indicated for fetuses with the following:

• Moderate or severe hydronephrosis

• Bilateral involvement

• Progression and/or persistence of hydronephrosis

• Normal amniotic fluid volume: Fetuses with unilateral involvement and normal amniotic fluid volume should have repeat prenatal ultrasonography examination at 32-34 weeks of gestation to evaluate and guide postnatal evaluation.

• Bilateral hydronephrosis and normal amniotic fluid volume: These patients should have repeat ultrasonography examination 2-3 weeks after diagnosis to evaluate for progression and amniotic fluid volume. Follow-up examinations are determined according to the serial ultrasonography results.

For follow-up in older children with hydronephrosis, most protocols recommend serial monitoring with ultrasound and diuretic renography. Indications for surgery include worsening of hydronephrosis, lithiasis, recurrent infections, or deterioration of renal function. Although diuretic renography remains the gold standard for the diagnosis of obstructive hydronephrosis, the use of color Doppler ultrasound to determine hydronephrosis grading and the absence of ureteral jets offers an accurate and noninvasive option that can limit the need for renography.[46]