202
			Practical Urology: EssEntial PrinciPlEs and PracticE
	Issues in Patient Management		Saline or contrast material is infused at 10 mL/
			min into the renal access, while pressures within
	Diagnostic Imaging		the kidney and bladder are monitored.
			Intravesical pressure is subtracted from intrare­
	Ultrasound		nal pressure and a difference between these pres­
			sures greater than 22 cm H2O is considered
	Ultrasound imaging is frequently utilized in the		obstructive, 15–22 cm H2O is considered inde­
	diagnostic management of suspected renal		terminate, and less than 15 cm H2O is considered
	obstruction.Ultrasound can easily detect hydro­		nonobstructive. The Whitaker test is associated
	nephrosis, and the addition of color Doppler		with poor sensitivity and specificity for renal
	duplex sonography allows noninvasive assess­		obstruction and is rarely utilized today.62
	ment of renal perfusion.57 Ultrasound is advan­
	tageous in that it is noninvasive, portable,		Nuclear Renography
	relatively inexpensive, and does not require ion­		Radionucleotide imaging provides a noninva­
	izing radiation, or contrast media.58 Ultrasound
	has the potential to detect characteristics of		sive means to assess for renal obstruction and
			differential renal function. The current radiop­
	renal parenchymal disease that may be associ­
			harmaceutical of choice is Tc­99m MAG3.63
	ated with obstruction such as increased echoge­
	nicity, loss of corticomedullary differentiation,		Adequate hydration is essential prior to the
			study as dehydration can mimic renal obstruc­
	or cystic disease.
			tion. Bladder catheterization is required in
	Doppler ultrasound can be utilized to calcu­
			patients with neurogenic or surgically altered
	late the resistive index (RI), which is defined as
			bladders, vesicoureteral reflux, lower urinary
	(peak systolic velocity­lowest diastolic velocity) /
			tract obstruction, or pelvic kidneys.63 Standard
	peak systolic velocity.59 A RI above 0.70 has been
	thought to be associated with renal obstruc­		diuretic renography involves administration of
			furosemide 20 min after injection of the
	tion.58 In diagnosing obstruction in adults with
	renal dilatation, an RI above 0.70 has 92% sensi­		radiotracer. In patients with equivocal results,
			administering furosemide 15 min before the
	tivity and 88% specificity.59 In children with
	hydronephrosis, the sensitivity of RI to diagnose		radiotracer can improve sensitivity and specific­
			ity for obstruction.64,65
	obstruction decreases to 82% and specificity
			Obstruction is assessed by determining the
	decreases to 63%.60
			time it takes for 50% of the radiotracer to clear
	Intravenous Urography		from the kidney (t1/2). In a standard renogram
			where furosemide is administered 20 min after
	Over the last couple of decades, intravenous		radiotracer injection: t1/2 greater than 20 min is
	urography (IVU) has been replaced by other		consistent with obstruction, t1/2 between 10 and
	imaging modalities. IVU provides anatomic		20 min is equivocal, and t1/2 less than 10 min is
	information such as degree of hydronephrosis		normal.66 These values will change if other
			methodology is used.For example,if furosemide
	and possible level of obstruction, and also func­
			is administered 15 min before the radiotracer:
	tional information. IVU may be particularly
			t1/2 greater than 10 min is consistent with
	useful in diagnosis of calyceal obstruction (e.g.,
	calyceal diverticulum), or complex duplex or		obstruction, t1/2 between 5 and 10 min is equivo­
	ectopic ureteral anatomy. Since it is dependent		cal, and t1/2 less than 5 min is normal.66
	upon renal excretion of contrast medium, IVU
	should not be used in patients with renal insuf­		Computed Tomography
	ficiency or patients with contrast allergy.		Unenhanced computed tomography (CT) is the
	Antegrade Urography and the Whitaker Test		most accurate radiologic study for the diagnosis
			of renal calculi with a sensitivity of 97% and a
	The Whitaker test was first described in 1973 to		specificity of 96%.67 CT is able to image all types
	diagnosis upper urinary tract obstruction, but is		of radiolucent calculi with the exception of pro­
	currently not commonly used.61 A percutaneous		tease inhibitor stones.68 Utilization of intrave­
	renal catheter and bladder catheter are placed.		nous contrast in CT is useful for anatomical