Obstructed Megaureter Workup

Updated: Dec 26, 2016
  • Author: Robert A Mevorach, MD; Chief Editor: Edward David Kim, MD, FACS  more...
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Workup

Laboratory Studies

Sequential Multiple Analysis–6 different serum tests

Consider the following:

  • Sequential Multiple Analysis–6 different serum tests (SMA-6) includes measurement of creatinine and BUN to assess gross renal function.

  • Levels of sodium, potassium, chloride, or bicarbonate may show subtle changes in some patients with bilaterality or associated dysplasia.

  • In neonates, wait 3-5 days to evaluate the baby’s kidney function rather than the mother's kidney function.

  • A creatinine level of 1 mg/dL or greater at age 1 year is prognostic for subsequent renal failure.

  • A serum calcium assessment for associated ureteral calculi is an essential screening test for hyperparathyroidism.

Urinalysis

Urinalysis is recommended upon evidence of infection, proteinuria, high pH level, and low specific gravity that may reflect underlying infection or renal dysplasia or damage. Urinalysis is used to screen for urinary tract infection (UTI) and assess urine concentration and acidification in bilateral lesions and dysplasia.

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Imaging Studies

On renal or bladder ultrasonography (see the imafes below), prenatal imaging reveals both hydroureter and hydronephrosis. Repeat ultrasonography for hydronephrosis within the first few days of life in patients with solitary kidney or bilateral lesions. Hydroureter and unilateral lesions may be evaluated electively within the first 2 months of life.

This renal sonogram demonstrates hydronephrosis wi This renal sonogram demonstrates hydronephrosis with good parenchymal thickness and retained corticomedullary differentiation.
This pelvic sonogram reveals the classic spindle c This pelvic sonogram reveals the classic spindle configuration of primary obstructed megaureter.

Postnatal imaging is used to define the degree of hydronephrosis based on the following Society of Fetal Urology guidelines:

  • Grade I - Splitting of the renal sinus more than 10 mm

  • Grade II - Splitting of the renal sinus more than 10 mm in an extrarenal or intrarenal pelvis not extending to the calyces

  • Grade III - Dilatation extending into the calyces without cortical thinning

  • Grade IV - Dilatation extending into the calyces with cortical thinning

Postnatal imaging further defines the following anatomy:

  • Extent of hydroureter, presence of collecting system duplication

  • Presence or absence of ureterocele

  • Bladder configuration, size, and thickening

Postnatal imaging further provides clinically relevant data, including the following:

  • Presence or absence of calculi

  • Echogenic debris suggesting infection

  • Indirect evidence of degree of obstruction by presence of a ureteral jet

  • Location and condition of remaining renal units

Voiding cystourethrography (VCUG) is performed to assess for the presence of vesicoureteral reflux and to further delineate the anatomy of the bladder and outlet. In boys with bilateral megaureter, posterior urethral valves must be excluded.

Radionuclide renal scanning

After ultrasonography and VCUG are performed, the diagnosis of primary megaureter may be secure; the only remaining clinical issue is evaluating for obstruction. In these cases, technetium Tc 99m diethylenetriamine pentaacetic acid (DTPA) or technetium Tc 99m mercaptotriglycylglycine (MAG-3) renal scanning may be used to assess renal blood flow, relative function, and drainage. It is also helpful in predicting the capacity for functional recovery prior to surgery.

Increasing ureteral dilation warrants consideration of renal and ureteral drainage. Although kidney drainage may be normal, it may be the result of urine pooling in the abnormally dilated ureter, resulting in ureteral obstruction.

Exact definitions of obstruction do not exist. Serial examinations to demonstrate a trend toward decreasing function or delayed drainage are often required to establish an accurate treatment approach. In addition, renal resistive index can be used to help identify true obstruction as long as renal function is good. [7]

This panel from a technetium Tc 99m mercaptotrigly This panel from a technetium Tc 99m mercaptotriglycylglycine (MAG-3) renal scan shows differential obstruction of each kidney. While the classic image of a primary obstructed megaureter is shown on the left, a severe congenital ureteropelvic junction obstruction is present in the contralateral kidney. (These images are viewed with the left kidney on the left portion of each panel and the right kidney on the right portion of each panel.)

Intravenous urography: In cases in which anatomic definition is desired, intravenous urography (IVU) can be used if renal function is good and the degree of obstruction to the affected renal unit is mild.

Magnetic resonance imaging: In centers that have the technology, MRI can be used to reconstruct a 3-dimensional depiction of the urinary collecting system. The requirement for special software to assess renal function accurately and the need for restraint, sedation, or general anesthesia limit its application in neonates and infants.

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Diagnostic Procedures

Antegrade injection of contrast directly into the renal pelvis via percutaneous access is used as an adjunct to placement of a nephrostomy tube to drain an infected system or to define an equivocal obstruction (Whitaker test) by infusion of contrast medium at a fixed rate with concurrent pressure measurements in the kidney and bladder. Infusion rates for adults generally have been 10 mL per minute, and a pressure differential between kidney and bladder of less than 15 cm H2 O is accepted as normal. This study is often used to provide additional evidence of obstruction to support surgical intervention. This technique also helps to delineate anatomy when diagnostic questions persist after less-invasive testing, often in the same setting as planned surgical repair.

As is evident from the 600-mL/h rate of urine flow that is used in the Whitaker test, the physiologic implications of all except negative test results are debatable. In the author's experience, this test is too dependent on variations in anatomy (renal collecting system compliance) and technique to provide any real benefit over a gestalt from antegrade pyelography alone.

Retrograde pyelography involves placement of a catheter into the ureteral meatus via endoscopy with injection of contrast medium under real-time fluoroscopy. It is reserved for diagnostic dilemmas and as an adjunct to surgery.

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Histologic Findings

Surgical pathology reveals 5 histologic types: (1) abnormal circular orientation of muscle fibers with hypertrophy and hyperplasia, (2) mural fibrosis with little normal muscle within the ureteral wall, (3) hypoplasia and atrophy of all ureteral musculature, (4) absent longitudinal musculature, and (5) normal ureteral anatomy.

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