eMedicine Specialties > Urology > Hydronephrosis and Ureter Disorders

Hydronephrosis and Hydroureter: Differential Diagnoses & Workup

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
Contributor Information and Disclosures

Updated: Feb 25, 2008

Differential Diagnoses

Other Problems to Be Considered

Extrarenal pelvis
Peripelvic cyst
Congenital megacalyces
Calyceal diverticula

Workup

Laboratory 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.

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