Urodynamics

Urodynamics

Sally E. Mitchell

Causes of nonobstructive dilatation of the renal collecting system include vesicoureteral reflux, urinary tract infection, previous obstruction, congenital malformations, and a noncompliant bladder. Distinguishing between obstructive hydronephrosis and nonobstructive dilatation presents a problem in a number of clinical scenarios. Anatomic evaluation by means such as ultrasonography measures the degree of dilatation but does not delineate the degree of obstruction. Often, this differentiation can be made using radiologic tests such as diuretic renography and intravenous urography, as well as retrograde pyelography. However, these tests sometimes fail to conclusively determine whether an anatomic obstruction exists. It is in such cases that urodynamics can prove most useful.¹

The renal collecting system and ureters are components of a dynamic system, and it is the resistance within this system that must be taken into account in determining whether an obstruction exists. Poiseuille’s equation, which originally characterized the flow of fluid through rigid tubes, has been adapted to physiologic systems. This law describes the relationship between resistance, flow, and pressure. Specifically, resistance through any conduit is directly proportional to pressure and indirectly proportionate to flow. Urodynamic studies, therefore, serve an optimal role in the evaluation of the renal collecting system and ureters because they deal directly with both the pressure and flow of fluid through these systems.

Indications

• Congenital megaureter—obstructed or nonobstructed?2,3

• Congenital megacalyces ⁴

• Congenital ureteropelvic junction obstruction—severe enough to require surgical repair?5,6

• Any congenital hydronephrosis requiring assessment for obstruction (Fig. 145-1)

FIGURE 145-1 This 2-year-old boy presented with bilateral hydronephrosis. Despite bilateral nephrostomies (including two placed in different calyces on the right) and a Foley catheter, his ureters remained very dilated. To assess the ureterovesical junction for obstruction, a urinary Whitaker test was requested. A, Supine view of left collecting system during left urinary Whitaker test. Note hydronephrosis on left, dilated ureter, and trabeculated bladder. B, Supine view of right collecting system during right urinary Whitaker test. Note hydronephrosis on right, dilated and very tortuous right ureter, and more filled view of extremely trabeculated bladder. C, Pediatric urinary Whitaker test form filled out for this patient’s height (length) of 82 cm and weight of 10.9 kg. By using the DuBois chart for finding body surface area, a straight edge is placed between patient’s height and weight to cross the surface area, which can be read off the nomogram. A standard glomerular filtration rate (GFR) can be chosen by patient’s age. These numbers are then used to calculate patient’s maximal physiologic urine output per kidney in milliliters per minute. This is the rate at which urinary Whitaker test should be infused to match the rate at which kidney produces urine. In this patient, we had estimated 5 mL/min. Using the form, his rate calculated to be 4 mL/min. (In actuality, his rate of infusion should probably have been even lower because his creatinine value was 0.8 owing to chronic renal obstruction. Using the Schwartz formula, his estimated GFR was only 56.1. Using this GFR in the calculation would have calculated his maximal physiologic urine output per kidney to be 1.8 mL/min! However, keep in mind that the point of this pediatric form is to avoid infusing the adult rate of 10 mL/min in small children to avoid infusing renal pelvis above patient’s physiologic rate, which could result in collecting system rupture if there is obstruction.) Pressure results and nephroureterograms demonstrate that this patient had no ureteral obstruction but had a very trabeculated bladder with a low capacity, consistent with previously undiagnosed posterior urethral valves.

• Postoperative ureteropelvic junction repair. Is the urine draining well antegrade through the repair? This is often difficult to assess because the renal pelvis will remain large and baggy owing to the previous chronic obstruction.7,8

• Postoperative distal ureteral reimplantation. This also may be difficult to assess if the upper collecting systems remain large or dilated from previous obstruction.

• Postoperative balloon dilatation of urinary stricture

• Assessment of ureteral strictures after injury, either traumatic or surgical (Fig. 145-2)

FIGURE 145-2 This 52-year-old woman presented with a history of right ureteral injury 8 years earlier after a hysterectomy. Obstruction was managed with nephrostomies, attempted nonsurgical management, and repair. Eventually, patient underwent ureteral reimplant but developed right flank pain again and had a new hydronephrosis managed by a stent. She improved clinically, but her intravenous pyelogram showed a narrowing in the mid- to distal ureter. She was referred from an outside hospital for evaluation and a urinary Whitaker test. A, Prone image of right renal collecting system accessed with a 21-gauge needle from flank approach into lower pole posterior calyx. Note nondilated collecting system and rapid filling of ureter. Needle was exchanged over 0.018-inch guidewire for inner sheath of a Jeffrey set (5F) with multiple side holes punched near end of sheath for good pressure measurements. If a nephrostomy or nephroureteral stent or any ureteral interventions were needed, this access would be excellent for proceeding with definitive management. B, Prone image of right renal collecting system during urinary Whitaker test. Note tightly narrowed distal ureter with slight dilation above, and bladder filled with contrast medium.

• Assessment of malignant obstruction resolution after chemotherapy or irradiation

• Transplant kidneys with question of obstruction (Fig. 145-3)^9–11

FIGURE 145-3 A, Transplant ureteral stricture in 10-year-old boy with history of autosomal-recessive polycystic kidney disease and living related kidney transplant 3 weeks previously. B, After crossing stricture, it was carefully dilated with a 2-mm and then a 4-mm balloon to allow placement of an 8F nephroureteral stent. C, After stenting stricture for 6 weeks, then changing stent to a nephrostomy tube in renal pelvis, patient went home for 2 weeks of a clinical trial. This image taken during urinary Whitaker procedure done after clinical trial. Pressure in renal pelvis for this image is 23 cm H₂O, with bladder pressure of 11 cm H₂O, for a differential pressure of 12 cm H₂O. Note good flow of contrast medium into bladder.

• Equivocal results from less invasive tests ¹²

• Suspected obstruction in presence of poor ipsilateral renal function ¹²

• Continued loin pain with upper urinary tract dilatation and a nonobstructive diuresis renogram ¹²

• Unexplained loin pain that might be due to intermittent obstruction at high urine flow rates ¹²

• Definitive investigation of the grossly dilated upper urinary tract where there is concern about the implications of an obstructive diuresis renogram with minimal symptoms ¹²

FIGURE 145-2 C, Whitaker test pressures for this patient. Differential pressures ranged between 1 and 3.5 cm H₂O, clearly normal for this patient despite visible ureteral narrowing. The 5F sheath was then removed; patient experienced no hematuria or fever and was subsequently able to be discharged.

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Tags: Image-Guided Interventions Expert Radiology Series

Dec 23, 2015 | Posted by admin in INTERVENTIONAL RADIOLOGY | Comments Off

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