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Hydronephrosis and Hydroureter
Article Last Updated: Feb 25, 2008
AUTHOR AND EDITOR INFORMATION
Section 1 of 10  
Author: Srinivas Vourganti, MD, Staff Physician, Department of Urology, Case Western Reserve University, University Hospitals of Cleveland
Coauthor(s):
Prakash Maniam, MD, Staff Physician, Department of Urology, St Mary's Hospital of Troy
Editors: Richard A Santucci, MD, FACS, Chief of Urology, Detroit Receiving Hospital; Specialist-in-Chief of Urology, Detroit Medical Center; Chief of Urologic Trauma Surgery, Sinai Grace Hospital; Director, The Center for Urologic Reconstruction; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; J Stuart Wolf, Jr, MD, FACS, David A Bloom Professor of Urology, Director, Division of Minimally Invasive Urology, Department of Urology, University of Michigan Medical Center; Stephen W Leslie, MD, FACS, Founder and Medical Director of the Lorain Kidney Stone Research Center, Clinical Assistant Professor, Department of Urology, Medical College of Ohio
Author and Editor Disclosure
Synonyms and related keywords:
hydronephrosis, hydroureter, urinary tract obstruction, renal pelvis dilation, calyces dilation, hydroureteronephrosis, hydronephrotic system, pyonephrosis, urine flow interruption, interrupted urine flow, pyelolymphatic backflow, renal colic, advanced pelvic malignancy, prostatic hypertrophy, prostate cancer, cervical cancer, pregnancy, ureter calculi, ureteral calculi, ureteropelvic junction obstruction, UPJ obstruction, urine reflux, postobstructive diuresis
Background
Hydronephrosis and hydroureter are common clinical conditions encountered not only by urologists but also by emergency medicine specialists and primary care physicians. Hydronephrosis is defined as a dilation of the renal pelvis and calyces. Analogously, hydroureter is defined as a dilation of the ureter. The presence of hydronephrosis or hydroureter should be considered a physiologic response to the interruption of the flow of urine. Although this is often due to an obstructive process, in some cases, such as megaureter secondary to prenatal reflux, the collecting system may be dilated in the absence of obstruction. In addition, obstruction can sometimes occur in the absence of a dilated urinary tract. Thus, the terms hydronephrosis and obstruction should not be used interchangeably. Hydronephrosis and hydroureter can range from benign processes, such as the physiologic hydroureteronephrosis of pregnancy, to potential life-threatening situations, such as infected hydronephrosis or pyonephrosis. Although patients usually present with some signs or symptoms, hydronephrosis can be an incidental finding encountered during the evaluation of an unrelated process. If unrecognized or left untreated, hydronephrosis and hydroureter secondary to obstruction can lead to hypertension, loss of renal function, and sepsis. Consequently, all patients found to have hydronephrosis or hydroureter should undergo a thorough evaluation and should be referred to a urologist.
Pathophysiology
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, chronic hydronephrosis is a situation in which 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.
Frequency
United States
The frequency of hydronephrosis in a large autopsy series, ranging from birth to age 80 years, was 3.1%. The prevalence rate was 2.9% in females and 3.3% in males.
Mortality/Morbidity
- Long-standing hydronephrosis may be associated with obstructive nephropathy and renal failure.
- Urinary stasis may result in infection, renal scarring, calculus formation, and sepsis.
- Renovascular hypertension may result from renin secretion from the hydronephrotic kidney. The incidence rate of hypertension after acute unilateral obstruction has been reported to be 20-30%. In patients with unilateral obstruction and hypertension, the hypertension can be reversed with treatment of the obstruction. Reversal of the hypertension is most likely to occur if an increase in renin production is measured in the hydronephrotic kidney along with a decrease in renin secretion from the contralateral kidney. Also, these patients demonstrate ACE-inhibitor–responsive hypertension. Therefore, if lateralizing renin secretion can be demonstrated, then the obstruction should be treated to normalize blood pressure.
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
History
- Symptoms vary depending on whether the hydronephrosis is acute or chronic.
- With acute obstruction, patients may present with pain, which is usually described as severe, intermittent, and dull. Patients may describe worsening of pain with consumption of fluids. Depending on the level of hydroureter, pain may radiate to the ipsilateral testicle or labia. Often associated with nausea and vomiting, pain from an obstructed system is referred to as renal colic.
- 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.
- A history of 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.
- Bilateral symmetrical hydronephrosis usually suggests a cause related to the bladder, such as retention, prostatic blockage, or severe bladder prolapse.1
Physical
- 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.
Causes
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
- Functional
- Extrinsic
- Bladder
- Intrinsic
- Functional
- Extrinsic - Pelvic lipomatosis
- Urethra
- Intrinsic
- Extrinsic - Benign prostatic hyperplasia and prostate cancer
Other Problems to be Considered
Extrarenal pelvis
Peripelvic cyst
Congenital megacalyces
Calyceal diverticula
Lab Studies
- Urinalysis: 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: Leukocytosis may indicate acute infection.
- Serum chemistry: Bilateral hydronephrosis and hydroureter can result in an elevation of BUN and creatinine levels. In addition, hyperkalemia can be a life-threatening condition.
Imaging Studies
- Ultrasonography
- Ultrasonography is a rapid, inexpensive, and reasonably accurate method of detecting hydronephrosis and hydroureter; however, accuracy can depend on the user. Ultrasonography generally serves as the preferred screening test to establish the diagnosis of hydronephrosis.
- Ultrasonography is inferior to other modalities for identifying the presence, source, or duration of obstruction. A chronically obstructed system may remain dilated long after the obstructive process resolves.
- Intravenous pyelography
- Intravenous pyelography (IVP) is useful for identifying both the presence and cause of hydronephrosis and hydroureter. Intraluminal causes are identified most easily based on IVP findings.
- In addition to its ability to delineate renal and collecting system anatomy, the IVP is also a functional study. The functional status of a chronically obstructed kidney can be assessed with both the timing (prompt/symmetric vs delayed/asymmetric) and intensity of the resulting nephrogram and pyelogram.
- Excretion of contrast for an IVP study requires intact renal function. In general, a serum creatinine level of less than 2 mg/dL is needed. In addition, such patients are at increased risk for contrast nephropathy, further limiting its usefulness in such settings.
- Another limitation of IVP is that, in cases of severe or long-standing obstruction, visualization of the ureter may be inadequate and the point of obstruction may not be apparent.
- While once considered the criterion standard of upper urinary tract imaging, the IVP is slowly being replaced by axial imaging modalities.
- CT scanning
- CT scanning has an important role in the evaluation of hydronephrosis and hydroureter.
- Retroperitoneal processes causing extrinsic obstruction of the ureter and bladder are evaluated best on CT scans.
- Unenhanced helical CT scanning is currently the imaging modality of choice to assess for a possible calculus. It provides 97% sensitivity, 96% specificity, and 97% overall accuracy in diagnosis of stones. Many stones that were once considered radiolucent (eg, uric acid stones) are readily apparent on CT scans. One exception is stones that are composed of HIV protease inhibitors (indinavir), which are not visible on CT scans.
- Contrast-enhanced CT scanning may also be used to evaluate hydronephrosis in patients with intact renal function. Three-dimensional reconstruction of the excretion phase of contrast (CT urography) may be performed to better evaluate the anatomy of intrinsic causes of hydronephrosis and hydroureter.
- Radionuclide studies
- Findings from radionuclide studies may be used to measure differential function and, therefore, are useful for treatment planning. A functional obstruction can be differentiated from an anatomic cause.
- Findings from diuretic renography can help determine whether an obstruction is present or absent in a hydronephrotic kidney. In this study, furosemide (Lasix) (1 mg/kg) is administered after approximately 20 minutes into the study if washout appears delayed.
- The assessment of renal blood flow provides a sense of whether function may return upon relief of the obstruction. However, images from these scans lack the resolution to define a site of obstruction.
- An advantage to nuclear renography is that it may provide useful information when iodinated contrast is not appropriate (eg, renal insufficiency, contrast allergy).
- MRI: Generally, MRI has a limited role in the workup of hydronephrosis and hydroureter because of long acquisition time and cost. However, in the setting of pregnancy, in which ionizing radiation should be avoided, MRI may have a role. MR urography (MRU) can be used as a safe adjunct to ultrasonographic evaluations to help distinguish physiologic from pathologic causes of hydronephrosis and hydroureter. Specifically, MRU can offer the clinician great detail as to the specific size and location of obstruction, if present. In addition, MRU can be used when an obstruction is identified but CT imaging has excluded stone disease. In this setting, MRU can replace more invasive modalities such as retrograde pyelography to elucidate the cause of obstruction.
- Plain film
- Although a routine kidney, ureter, bladder (KUB) scan with all CT scans is not necessary, KUB scan images are helpful for classifying a stone as radiodense or radiolucent.
- Also, obtaining KUB images before a planned treatment such as lithotripsy is helpful to assess for migration of the stone.
Procedures
- Retrograde pyelography may be performed on patients with contrast allergy to opacify the entire upper collecting system; however, risks associated with anesthesia and the risk of infection are present. In cases of severe or long-standing obstruction, the ureter may not be visualized on IVP images, and a retrograde pyelogram would demonstrate the location and nature of the obstruction.
Medical Care
The role of medical treatment of hydronephrosis and hydroureter 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.2
Surgical Care
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. 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.
- 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.
Consultations
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. Also, an interventional radiologist would be needed for nephrostomy tube placement if urgent decompression is needed and ureteral stent placement is not possible.
Further Inpatient Care
- 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.
Further Outpatient Care
- 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, perform laboratory studies on renal function to assess the recovery of renal function.
Complications
- 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.
Patient Education
Medical/Legal Pitfalls
- Once the diagnosis of hydroureteronephrosis is made, immediately refer the patient to a urologist. Delay in referral could result in irreversible loss of renal function.
- If bladder outlet obstruction is the cause of the hydroureteronephrosis and a large volume is drained, the catheter should be left in place, with a leg bag. Severe bladder distention can be associated with impaired detrusor function for the first few days after relief of obstruction. The catheter allows drainage during this recovery period.
- Before performing any invasive procedure to relieve an obstructed system, assess the degree of function in the contralateral kidney.
Special Concerns
- Hydronephrosis and hydroureter during pregnancy are physiologic and are most pronounced during the third trimester. This is believed to be due to mechanical obstruction by the gravid uterus and the effects of increased progesterone levels.
The authors and editors of eMedicine gratefully acknowledge the contributions of previous coauthor Martin I Resnick, MD †, to the development and writing of this article.
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Hydronephrosis and Hydroureter excerpt Article Last Updated: Feb 25, 2008
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