Ureteropelvic Junction Obstruction Workup

Updated: Aug 06, 2021
  • Author: Michael Grasso, III, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Workup

Laboratory Studies

All patients with possible ureteropelvic junction (UPJ) obstruction should be evaluated with the following laboratory studies:

  • Complete blood cell count (CBC)
  • Coagulation profile
  • Electrolyte levels
  • Kidney function assessment - Blood urea nitrogen (BUN) and serum creatinine levels
  • Urine culture
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Imaging Studies

Neonates who present with hydronephrosis should be fully evaluated with voiding cystourethrography (VCUG; to rule out vesicoureteral reflux) and renal ultrasonography (see image below) soon after birth. These patients should also be placed on prophylactic antibiotics (amoxicillin 15 mg/kg) to prevent urinary tract infections (UTIs), especially while diagnostic imaging is being performed.

Intraluminal sonogram of ureteropelvic junction ob Intraluminal sonogram of ureteropelvic junction obstruction demonstrating multiple crossing vessels.

If renal ultrasonography demonstrates hydronephrosis without reflux on VCUG, a diuretic renal scan (mercaptotriglycylglycine [MAG-3], diethylenetriamine [DTPA], or dimercaptosuccinic acid [DMSA]) should be performed to quantify relative kidney function and to define the extent of obstruction. Renal ultrasonography and VCUG are performed in children with suspected UPJ obstruction.

Historically, intravenous pyelography (IVP) was used to evaluate patients with possible UPJ obstruction. However, in the evaluation of a child with a hydronephrotic kidney, diuretic renography has taken the place of IVP. The benefits of diuretic renography are that iodine-based intravenous contrast is not used, radiation exposure is minimal, and kidney function can be better quantified. The disadvantage of the nuclear medicine scan is that insight into renal anatomy is not obtained.

In 1992, the Society for Fetal Urology and the Pediatric Nuclear Medicine Council published guidelines for the "Well-Tempered Diuresis Renogram." [3] Standardized protocols for hydration, radiopharmaceuticals, bladder catheterization, diuretic dose, timing of diuretic, and determination of clearance half-time (T1/2) have been established.

Functionally significant obstruction is often diagnosed with diuretic renal scanning. The conventional renographic criteria include a flat or rising washout curve after diuretic with T1/2 of greater than 20 minutes and differential function of less than 40. Studies suggest that measurement of P40 (percent tracer clearance at 40 minutes) may be more sensitive in assessing clinically significant renal obstruction. [4] This particular assessment has the benefit of using an existing diagnostic study. The differential function is important in determining the need for intervention, especially in asymptomatic patients, and in selecting the appropriate treatment (pyeloplasty vs nephrectomy).

Poorly functioning kidneys (< 10%) are often best treated with nephrectomy; however, studies by Nishi (2016) and Singla (2016) have demonstrated evidence of good functional outcomes with pyeloplasty, despite age and low preoperative renal split functions (less than 25%). [5, 6] Additionally, a retrospective review by Li et al that utilized multivariate analysis comparing factors of age, renal pelvis type, and renal resistive index concluded that preoperative differential function cannot independently predict postoperative recoverability of kidney function. [7]

The evaluation of ureteral anatomy is difficult with nuclear medicine renal scanning. In adult patients, IVP is more commonly used to outline this anatomy and can often replace nuclear medicine scanning altogether. See the images below. However, nuclear medicine scanning is also used to assess outcomes after surgical intervention.

Intravenous pyelogram demonstrating ureteropelvic Intravenous pyelogram demonstrating ureteropelvic junction obstruction with dilatation of the collecting system and non-visualization of the ureter on delayed imaging.
Retrograde pyelogram demonstrating ureteropelvic j Retrograde pyelogram demonstrating ureteropelvic junction obstruction secondary to annular stricture.
Retrograde pyelogram demonstrating ureteropelvic j Retrograde pyelogram demonstrating ureteropelvic junction obstruction secondary to crossing vessels.

Multidetector computed tomography (CT) scanning with three-dimensional reconstruction may be used to help establish the anatomy of UPJ obstruction and associated vessels. In children, retrograde ureteropyelography is sometimes performed to define the entire ureter just prior to surgical repair. Contrast-enhanced color Doppler imaging is recommended by some as a useful imaging modality for the detection of crossing vessels in patients with UPJ obstruction.

Dynamic contrast-enhanced magnetic resonance urography (MRU) is the latest imaging modality used in assessing UPJ obstruction. In children, this study offers the advantages of no radiation exposure and excellent anatomical and functional details with a single study. The study also provides details of renal vasculature, renal pelvis anatomy, location of crossing vessels, renal cortical scarring, and ureteral fetal folds in the proximal ureter.

Recent criteria for diagnosis of UPJ obstruction on MRU include fluid levels on delayed contrast-enhanced scans and the presence of swirling contrast material on the dynamic images. MRU using a time-resolved, data-sharing three-dimensional contrast-enhanced technique can demonstrate ureteral peristalsis and permits quantification of ureteral peristaltic frequency. [8]

Contrast-enhanced magnetic resonance angiography (MRA) had a sensitivity of 85%, a specificity of 80%, and a positive predictive value of 0.8 for the diagnosis of aberrant and obstructing renal arteries in a retrospective study of 19 pediatric patients with UPJ obstruction. [9]

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Diagnostic Procedures

When the workup results are equivocal, a Whitaker antegrade pressure-flow study may be performed to further evaluate for UPJ obstruction. This test begins with the placement of a small-diameter nephrostomy tube through the back and directly into the kidney. Dilute contrast medium is instilled, and the intrarenal collecting system is pressure-monitored. Under fluoroscopy, the UPJ is assessed and drainage through this segment is defined.

While function cannot be assessed, relative resistance and pressure within the renal pelvis can be measured. High intrarenal pressures define obstruction, while low pressures in the presence of hydronephrosis are consistent with normal variance. This is particularly useful in large dilated systems in which the renal pelvis must be completely full prior to drainage assessment. In this setting, nuclear medicine scanning can yield false-positive results.

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