The Whitaker test: experimental analysis in a canine model of partial ureteric obstruction

(99m)Tc-DTPA diuretic renal scintigraphy in cats with nephroureterolithiasis

The purpose of this study was to evaluate results of diuretic renal scintigraphy in 32 feline kidneys with nephroureterolithiasis and variable degrees of renal pelvis/ureteral dilation. Six kidneys showed a non-obstructive scintigraphic pattern, with a downward slope of time-activity curves (TAC) and a median excretion half-time of radiopharmaceutical (T((1/2))) of 6.09 (5.08-8.43) min. Eight kidneys showed an obstructive pattern, with a continuous rise of TAC and median T((1/2)) of -7.91 (-43.13-0.00) min. In one kidney with presumptive partial obstruction scintigraphic results were equivocal. Seventeen kidneys, most of which had an individual kidney glomerular filtration rate below 0.5ml/min/kg, had non-diagnostic studies. Diuretic renal scintigraphy may be a useful adjunct modality in the diagnosis of ureteral obstruction in some cats if renal function is maintained. However, the large number of non-diagnostic studies in animals with decreased renal function represents a clear limitation of the technique.

International Scientific Committee of Radionuclides in Nephrourology (ISCORN) consensus on renal transit time measurements

This report is the conclusion of the international consensus committee on renal transit time (subcommittee of the International Scientific Committee of Radionuclides in Nephrourology) and provides recommendations on measurement, normal values, and analysis of clinical utility. Transit time is the time that a tracer remains within the kidney or within a part of the kidney (eg, parenchymal transit time). It can be obtained from a dynamic renogram and a vascular input acquired in standardized conditions by a deconvolution process. Alternatively to transit time measurement, simpler indices were proposed, such as time of maximum, normalized residual activity or renal output efficiency. Transit time has been mainly used in urinary obstruction, renal artery stenosis, or renovascular hypertension and renal transplant. Despite a large amount of published data on obstruction, only the value of normal transit is established. The value of delayed transit remains controversial, probably due to lack of a gold standard for obstruction. Transit time measurements are useful to diagnose renovascular hypertension, as are some of the simpler indices. The committee recommends further collaborative trials.

Renal transit time with MR urography in children

PURPOSE

To prospectively evaluate use of dynamic contrast material-enhanced magnetic resonance (MR) urography for measurement of renal transit time (RTT) of a contrast agent through the kidney and collecting system so as to identify obstructive uropathy in children.

MATERIALS AND METHODS

One hundred twenty-six children suspected of having hydronephrosis were hydrated prior to undergoing both conventional and dynamic contrast-enhanced MR urography of the kidneys and urinary tract. A three-dimensional sequence was used to track passage of contrast agent through the kidneys. Time between the appearance of contrast material in the kidney and its appearance in the ureter at or below the level of the lower pole of the kidney was defined as RTT. Bland-Altman plots were used to quantify intra- and interobserver performance. In 30 children, a nuclear medicine renogram was also obtained, and the half-life of renal signal decay after furosemide administration was derived and compared with the MR imaging RTT by using receiver operating characteristic curves.

RESULTS

On the basis of RTT, kidneys were classified as normal (RTT </= 245 seconds), equivocal (245 seconds > RTT </= 490 seconds), or obstructed (RTT > 490 seconds). Inter- and intraobserver agreement indicated that the technique is both robust and reproducible. Receiver operating characteristic analysis for comparison of results of MR imaging and diuretic renal scintigraphy showed good agreement between the modalities, with a mean area under the curve of 0.90.

CONCLUSION

When used in conjunction with morphologic images obtained in the same examination, RTT generally allowed normal kidneys to be differentiated from obstructed and partially obstructed kidneys.

Pressure flow measurement of hydronephrosis in children: a new approach to definition and quantification of obstruction

PURPOSE

Hydronephrosis due to obstruction of the ureteropelvic junction is not uncommon in children. The critical level of outflow resistance characterizing obstruction remains to be established. It was previously found in our laboratory that the outflow resistance could be calculated in an animal model by servoregulating the infused flow to preset pressure levels. We determine whether this procedure is also feasible in patients with hydronephrosis.

MATERIALS AND METHODS

A total of 46 patients with 48 hydronephrotic kidneys were examined. There were 32 boys and 14 girls with a diagnosis of hydronephrosis and suspected ureteropelvic junction obstruction who underwent a pressure flow study under general anesthesia for evaluation before possible surgery. The kidney was punctured percutaneously under ultrasonic guidance, and the study was performed under fluoroscopy. Flow levels were measured when steady state flow was achieved at pressures 5, 10, 15, 20, 25 and 30 mm. Hg greater than the intra-abdominal pressure. A conventional Whitaker test at an infusion rate of 10 ml. per minute was performed for comparison. The patient then underwent pyeloplasty if the kidney was considered obstructed.

RESULTS

There were 2 patients excluded from evaluation because of significant leakage of contrast medium. Stable and repeatable recordings were obtained in all pressure flow studies but only in 7 of 46 Whitaker tests. A total of 41 kidneys were considered obstructed at pressure flow studies and operated on. The resistance was pressure dependent. Thus, mean resistance in the previous range 5 to 15 mm. Hg was considered a good overall measure of outflow resistance. Mean resistance less than 0.75 was normal and greater than 1.25 obstruction. There were 7 patients who had crossing vessels and a high mean resistance (3 or greater).

CONCLUSIONS

The Whitaker test proved to be of no value for calculating the outflow resistance in ureteropelvic junction obstruction. The pressure flow study is superior to the Whitaker test for determining the outflow resistance and also allowing categorization of ureteropelvic junction obstruction.

Constant elevation in renal pelvic pressure induces an increase in urinary N-acetyl-beta-D-glucosaminidase in a nonobstructive porcine model

PURPOSE

To clarify the physiological significance of renal pelvic pressure elevations encountered in the evaluation of hydronephrotic kidney we examined the effects of different levels of renal pelvic pressure on the induction of renal injury.

MATERIALS AND METHODS

A nonobstructive porcine model was created in which the urine drained against a constant predetermined pressure gradient. Renal pelvic pressure of 10, 20 and 40 cm. was created in 2, 2 and 4 animals, respectively. During 18 to 23 hours serial urinary N-acetyl-beta-D-glucosaminidase levels were determined as an indicator of renal tubular injury. Tissue specimens were examined histologically and renal arterial blood flow was monitored.

RESULTS

Urinary N-acetyl-beta-D-glucosaminidase levels in the kidneys subjected to 10 cm. water remained essentially unchanged. However, at 20 and 40 cm. water statistically significant increases were observed. Similarly, renal arterial blood flow was unchanged at 10 cm. water but it became significantly lower than in controls at 20 and 40 cm. water. Histological evaluation revealed mild to moderate tubular dilatation in the kidneys subjected to 20 and 40 cm. water.

CONCLUSIONS

Excessively high collecting system pressure induced renal cellular injury, as reflected by an increase in urinary N-acetyl-beta-D-glucosaminidase levels. While renal pelvic pressure up to 10 cm. water appeared to be innocuous, renal cellular injury was evident within as little as 1 hour at renal pelvic pressures 20 cm. water or greater. The degree of N-acetyl-beta-D-glucosaminidase in the urine also correlated with a decrease in renal arterial blood flow.

Evaluation of Doppler ultrasonography and dynamic contrast-enhanced CT in acute and chronic renal obstruction

The development of a reliable, minimally invasive method of distinguishing physiologically significant renal obstruction from dilation without obstruction would have important clinical implications. As it is well known that renal blood flow decreases over time in the presence of obstruction, we investigated the ability of color flow Doppler ultrasonography and dynamic contrast-enhanced CT scanning to detect changes in blood flow in unilaterally obstructed porcine kidneys. In the initial phase of this study, the effect of acute unilateral obstruction were studied in nine pigs. The resistive index (RI) was measured with Doppler ultrasonography, and renal blood flow was quantitated with dynamic CT using tracer kinetic principles and deconvolution. The RI measurements were unable to distinguish between the obstructed kidneys and their controls. Dynamic CT scanning demonstrated a greater fall in blood flow in the obstructed kidney, and this change was significantly different from baseline. The same findings were supported by radiolabelled microsphere blood-flow measurement. In the chronic portion of the study, after surgical creation of a partial ureteric obstruction, the kidneys were studied by both techniques at 1, 2, and 3 weeks. Again, RI was unable to demonstrate any difference between obstructed and unobstructed kidneys, while CT showed a progressive fall in blood flow in each successive week that was statistically significant. Dynamic contrast-enhanced CT scanning is a promising diagnostic tool that might be used to distinguish a functionally significant renal obstruction from nonobstructive dilation. Further clinical studies to validate this technique are warranted.

Imaging for ureteropelvic junction obstruction in adults

The three goals of imaging for ureteropelvic junction (UPJ) obstruction are to determine the presence and degree of renal obstruction, to assess renal function, and to determine the cause of the problem. The diagnostic techniques are intravenous urography, which is unreliable; ultrasonography, with the addition of pulsed Doppler technology; diuretic scintigraphy; and pressure-flow studies (Whitaker test), which is the only direct clinical test of renal outflow resistance. Voiding cystography, retrograde ureteropyelography, and CT have utility in some patients. In determining the cause of obstruction, the patient often is evaluated for crossing vessels using angiography, endoluminal ultrasonography, or spiral CT. It is not possible to formulate a single algorithm for radiographic evaluation of suspected UPJ obstruction, but in the average adult patient, urography and diuretic scintigraphy are sufficient.

Pressure decay half-life: a method for characterizing upper urinary tract urine transport

PURPOSE

We examined the pressure dynamics of hydronephrotic kidneys after elevated renal pelvic pressure developed.

MATERIALS AND METHODS

A total of 40 patients (44 renal units) 0.2 to 12 years old was evaluated. Transiently elevated renal pelvic pressure was induced with a percutaneous nephrostomy infusion. After renal pelvic pressure increased the infusion was stopped and the subsequent decrease in pressure with time was plotted as a pressure decay curve. The rapidity of the decrease in renal pelvic pressure was then quantitated as a half-life for each pressure decay curve. Pressure decay half-lives were compared to corresponding pressure flow study results and diuretic nuclear renography half-lives.

RESULTS

Renal units without elevated renal pelvic pressure during infusion at a high physiological flow rate were associated with relatively rapid pressure decay, whereas those with elevated renal pelvic pressure during infusion were associated with much slower pressure decay (p < 0.0001). Diuretic nuclear renography half-lives had no correlation with collecting system pressure dynamics.

CONCLUSIONS

Pressure decay half-life provides an objective quantitative measure of the relative tendency for elevated renal pelvic pressure to persist. When used in conjunction with other diagnostic modalities, it may be a useful parameter for a comprehensive assessment of the risk of pressure induced injury in hydronephrotic kidneys.

Renal resistive index in experimental partial and complete ureteral obstruction

RATIONALE AND OBJECTIVES

Recent clinical work suggests that the Doppler resistive index (RI) may be useful in distinguishing obstructive from nonobstructive hydronephrosis. We evaluated the usefulness of the RI in a rabbit model of hydronephrosis.

METHODS

Unilateral partial ureteral obstruction was produced in nine rabbits and complete obstruction in another nine. Three sham operations were performed, and these animals served as control subjects. The RI was measured in all kidneys before and 6 hr after surgery and on days 1, 4, and 7 postoperatively. The RI and the difference in RI (delta RI) between the obstructed and normal kidney were evaluated over time using a two-way analysis of variance. The intravenous urography and Whitaker tests served as gold standards.

RESULTS

Hydronephrosis was observed on sonograms in all obstructed kidneys. Comparing groups, there was no significant difference in mean RI or delta RI between the three groups at any time point. Looking at individual groups over time, there was no significant change in mean delta RI, whereas the change in mean RI was significantly elevated above baseline only in the complete obstruction group at 6 hr (p = .002) and on days 4 (p = .008) and 7 (p = .006). In evaluating varying thresholds of RI and delta RI, we could not consistently discriminate between normal and obstructed kidneys.

CONCLUSION

Although complete obstruction caused a significant increase in RI, partial obstruction failed to do so. RI and delta RI values proved to be insensitive predictors of obstruction in this rabbit model.

Renal haemodynamics and prostaglandin synthesis in partial unilateral ureteric obstruction

Haemodynamic changes in partial unilateral ureteric obstruction (PUUO) may be related to altered prostaglandin synthesis. In 12 dogs the left ureter was partially obstructed for 5 weeks. In six dogs the ureter was reimplanted into the bladder and to investigate the effect of this procedure on the contralateral side the other six animals underwent ipsilateral nephroureterectomy. Renal blood flow (RBF) was measured by the distribution of radiolabelled microspheres. Changes in urinary prostaglandin (PG) concentrations were validated by renin activity using angiotensin I. Reduced left RBF during obstruction was associated with increased thromboxane A2 synthesis (P < 0.01). Increased RBF to the non-obstructed side was associated with elevated PGE2 formation (P < 0.05). Elevated angiotensin I levels (P < 0.01) corresponded to maximal increases in PG synthesis. Reimplantation of the obstructed kidney did not exert a direct effect on contralateral RBF or PG concentration. Haemodynamic changes in PUUO in vivo are associated with alterations in renal PGs.

Incidence, diagnosis, and treatment of ureteric stenosis in 1298 renal transplant patients

Of 1130 patients who had undergone a total of 1298 kidney transplantations, 40 developed a stenosis of the ureter (3.1%). In all of the transplants, the anastomosis between the ureter and the urinary bladder was established as extravesical ureteroneocystostomy. Up until 1984, in cases where an obstruction in the urinary tract was suspected, the diagnosis was made by an i.v. pyelogram or by nuclear scans of the transplant. Thereafter, in 28 patients, in cases of sonographically suspected stenosis of the ureter, the diagnosis was established by means of a simplified Whitaker test. Nearly one-half of the stenoses of the ureter developed within the first 3 months after transplantation. In five patients (12.5%) the stenosis developed significantly later, 3-10 years after kidney transplantation. Seventy percent of the stenoses were localized in the distal third of the ureter. About 75% of the surgically explored stenoses could be corrected by resection and reimplantation of the ureter. During the post-operative follow-up, restenosis occurred in three patients. At present, 62% of all patients whose ureteric stenoses were corrected have well-functioning kidney transplants.

Diuretic renography: concepts and controversies

Diuretic renography has proved to be a reliable, noninvasive test for the diagnosis of upper urinary tract obstruction. False positive and false negative results may occur but can be minimized by careful attention to technique. The timing of diuretic administration, state of hydration, and furosemide dosage appear to be the key methodologic variables.

An experimental technique for renal intrapelvic access

This study describes an experimental technique for insertion of an indwelling cannula into the canine renal pelvis, and demonstrates its use in the measurement of pelviureteric pressure and motility, creatinine clearance, Whitaker tests, nephrostograms and nephrostomy drainage. The system, which consists of cannula, Heplock and plastic fixation disc, has been inserted into 53 canine kidneys (48) dogs, and percutaneous needle passage into the subcutaneously placed Heplock was used to gain access to the renal pelvis. This technique was successful in virtually all cases (131 separate procedures), and there were few complications. The indwelling intrapelvic cannula is a simple, cheap and reliable method of gaining longterm renal intrapelvic access in the dog, and has many experimental applications.