Dilatation or hydrops does not always equate to obstruction.^1,2 This is an important concept. The upper urinary tract (UT) remains at different degrees of dilation for most patients who underwent ureteral reconstructive surgery, which makes it difficult to assess the obstruction.³ Failure to identify upper UT obstruction before removing the drainage tube may result in recurrent flank pain, fever, deterioration of hydronephrosis, impairment of renal function, and secondary intervention.

Traditional examinations, for instance, contrast-enhanced CT, MRI, and ultrasonography, rely mainly on the morphological changes to diagnose whether the UT is unobstructed. More difficult to interpret is the dilatation that remains after the relief of obstruction. Diuretic renography assesses the excretory function through radioisotopes and has been widely used since it was proposed.⁴ However, the test may be unreliable in a kidney with impaired function or associated with an extremely large collecting system. The response to a diuretic is also in doubt according to whether the damage is localized in glomerular or tubular.

In 1973, Whitaker advocated a constant perfusion flow study to distinguish whether UT dilatation was caused by obstruction.⁵ It is the lack of standardized procedures and its invasive manipulation that limit its application.^5,6 Based on the Whitaker test, we made the following improvements (Figure 1): (1) all patients were pre-placed with a nephrostomy tube for “ureteral rest” and protective drainage; (2) comprehensive evaluation was performed by expanding the range of perfusion velocity (1-20 mL/min) and taking into account the physiological phase and high load phase; and (3) the results were classified into 3 types (normal, critical, and obstructive) according to the imaging and pressure (type I, the pressure remains stable near the baseline throughout the perfusion process, and the reconstructed ureter is well visualized [Figure 2]⁷; type II, the renal pelvic pressure increases with perfusion, while urography shows the ureteral peristalsis still exists. At the end of the examination, the pressure difference is lower than 15 cm H₂O and the renal pelvis pressure is lower than 22 cm H₂O [Figure 3]; type III, the renal pelvic pressure and pressure difference increase with perfusion and exceed the normal level. At the same time, ureteral peristalsis is weak or absent [Figure 4]).

Figure 1. The schematic diagram of upper urinary tract videourodynamics.

Figure 2. Normal pressure and imaging of upper urinary tract videourodynamics (type I). Reprinted with permission from Li X et al. Urol J. 2021;19(1):56-62.⁷

Figure 3. Critical pressure and imaging of upper urinary tract videourodynamics (type II).

Figure 4. Obstructive pressure and imaging of upper urinary tract videourodynamics (type III).

In our preliminary results, UT videourodynamics (VUDS) has its unique role in assessing obstinate and equivocal hydronephrosis. The UT-VUDS classification helps determine the further strategy. All patients with type III received further treatment, including regular double-J stent replacement, Allium stent, ureteroscopic balloon dilation, ureteroneocystostomy, and ileal ureter. Ultrasound showed that the degree of hydronephrosis remained stable. Therefore, reintervention should be considered in patients with obstructive UT-VUDS (type III), with potential benefits in renal function. In critical UT-VUDS (type II), the upper UT has poor urination reserve function, and it is important to avoid holding urine or diuretic food and drugs. Renal function may fluctuate slightly, but not to the point where surgery is required. Overall, the sensitivity and specificity of the modified UT-VUDS in predicting the need for further treatment were 54.5% and 100%, respectively, and the area under curve was 0.747 (P = .007).

During the past decade, researchers have passed different judgments on the Whitaker test. Proponents have approved its values for the diagnosis of obstruction and exclusion of unobstructed dilatation. Johnston proposed the Whitaker test was useful in evaluating patients with skeptical ureteropelvic or ureterovesical junction obstruction.⁸ Lupton and George concluded that the Whitaker test contributed to the clinical management in 84% of the suspected upper UT obstructions.⁹ However, Djurhuus et al have shown that the resting pelvis pressure may show considerable overlap in a hydronephrotic or in a normal one.¹⁰ Wahlin et al also agreed the specificity of the method was limited.¹¹

Modified UT-VUDS has played a significant role in improving diagnostic accuracy and reducing false-positives. In the classic Whitaker test, the perfusion rate was constant at 10 mL/min, which came from healthy volunteers. However, the physiological urinary rate is 1-3 mL/min, and the urine output could easily exceed 10 mL/min in some specific conditions. The fixed compromising perfusion speed is not appropriate. In our modified UT-VUDS, the initial perfusion rate is 1-3 mL/min and gradually increases. This speed continues until the renal pelvis could be visualized on x-ray. After that, the perfusion rate gradually increases to 20 mL/min to determine whether there is a high flow obstruction.

The advantage of this study is utilizing perfusion manometry to quantify the excretion function of the ureter after upper UT reconstruction, taking into account the rate of urine production under different physiological conditions. Further grouping results have clinical application value for the diagnosis and treatment of stubborn dilatation of the ureter. On the other hand, postoperative urodynamics does not exert additional trauma on the patient.² In conclusion, obstinate dilation after upper UT reconstruction is a confusing condition that cannot be overlooked. The false-positive result of diuretic renography is worrisome. UT-VUDS evaluates the recovery of transport urine function of the reconstructed ureter through changes in morphology and pressure. It is suitable for patients with no significant improvement in the degree of hydronephrosis after reconstruction. The UT-VUDS classification helps determine the further treatment strategy. The noticeable increase in the upper UT pressure and poor contrast agent excretion suggests that the obstruction still exists, and the appropriate intervention should be taken in time.