Ureteropelvic Junction Obstruction: An Innovative Approach Combining Metallic Stenting and Virtual Endoscopy:

Metallic double pigtail ureteral stent usage during extracorporeal shock wave lithotripsy in the swine model: is there any effect on the ureter?

PURPOSE

To examine the safety and compatibility of full-length metal ureteral stent usage with extracorporeal shock wave lithotripsy (SWL).

METHODS

Four Resonance ureteral stents and four special Resonance ureteral stents modified to contain thermocouples were placed unilaterally in eight pigs, with contralateral ureter of each pig serving as its own control. All pigs were subjected to the same SWL protocol in both their ureters. In the animals containing the modified stents, ureter temperature was monitored during treatment. The animals were sacrificed on days 1 and 15 after treatment, and both their ureters were histologically examined.

RESULTS

No statistically significant increase (mean increase of 0.5 degrees C, p > 0.05) of stent temperature was observed during treatment. No differences in histology were observed among ureters containing stents and control ureters at both days 1 and 15 after treatment.

CONCLUSION

SWL appears to be harmless for the ipsilateral ureter.

Success of ureteral stents for intrinsic ureteral obstruction

PURPOSE

Previous reports suggest a high success rate for retrograde ureteral stenting for intrinsic ureteral obstruction, but few preoperative predictors of success have been offered. We reviewed our experience to look for factors that suggest failure of stents for intrinsic ureteral obstruction.

MATERIALS AND METHODS

We retrospectively reviewed the outcome of retrograde ureteral stent placement for intrinsic ureteral obstruction without concurrent or intended definitive management of the obstruction.

RESULTS

Thirty-eight patients treated for intrinsic ureteral obstruction, representing 41 ureteral units (UUs), were monitored for an average of 25.5 months. The overall success rate was 88%. Of the successes, 13 UUs had definitive therapy to permanently remove the cause of obstruction, obstruction resolved in 12 UUs after stent placement, and 11 UUs were managed with indwelling stents. Therapy failed in five UUs, with a median time to failure of 1.9 months. Of the UUs in which failure occurred, three failures were caused by misdiagnosis; in the remaining two, the stent did not correct the obstruction. On univariate analysis, male sex (P = 0.006), increased creatinine level as a presenting symptom (P = 0.002), and more severe preoperative hydronephrosis (P = 0.042) were predictive of failure. Adverse events were low, with complications from stenting occurring on only four of 41 UUs.

CONCLUSION

If initial stent placement was possible, intrinsic ureteral obstruction was managed successfully in 88% of patients. Given high success and minimal complications, retrograde placement of ureteral stents can be performed to treat patients with intrinsic ureteral obstruction. Treatment failure is more likely to occur in men and patients with severe hydronephrosis or an elevated creatinine level.

Virtual endoscopy of the urinary tract

Technological breakthroughs have advanced the temporal and spatial resolutions of diagnostic imaging, and 3 dimensional (3-D) reconstruction techniques have been introduced into everyday clinical practice. Virtual endoscopy (VE) is a non-invasive technique that amplifies the perception of cross-sectional images in the 3-D space, providing precise spatial relationships of pathological regions and their surrounding structures. A variety of computer algorithms can be used to generate 3-D images, taking advantage of the information inherent in either spiral computed tomography or magnetic resonance imaging (MRI). VE images enable endoluminal navigation through hollow organs, thus simulating conventional endoscopy. Several clinical studies have validated the diagnostic utility of virtual cystoscopy, which has high sensitivity and specificity rates in the detection of bladder tumor. Published experience in the virtual exploration of the renal pelvis, ureter and urethra is encouraging but still scarce. VE is a safe, non-invasive method that could be applied in the long-term follow-up of patients with ureteropelvic junction obstruction, urinary bladder tumors and ureteral and/or urethral strictures. Its principal limitations are the inability to provide biopsy tissue specimens for histopathologic examination and the associated ionizing radiation hazards (unless MRI is used). However, in the case of endoluminal stenosis or obstruction, VE permits virtual endoluminal navigation both cephalad and caudal to the stenotic segment. To conclude, VE provides a less invasive method of evaluating the urinary tract, especially for clinicians who are less familiar with cross-sectional imaging than radiologists.

Ureteral Metal Stents: A Tale or a Tool?

There are four types of ureteral metal stents: self expandable, balloon expandable, covered, and thermoexpandable shape-memory. Insertion of metal stents requires expertise with transurethral and percutaneous techniques. The stricture is traversed with the aid of a guidewire via a percutaneous nephrostomy, and the stenotic segment is dilated using a high-pressure balloon catheter. The stent is then inserted over the guidewire, such that the upper end bypasses the obstruction by at least 3 to 4 cm, while the lower end extends intravesically for 0.5 to 1 cm from the ureteral orifice. If necessary, two or more stents are placed in sequence, overlapping by at least 2 to 3 cm. Metal stents were initially used for the relief of end-stage malignant disease, and their role in the treatment of benign ureteral strictures is still undefined. Patients often complain of abdominal discomfort and mild pain after stent insertion, which soon resolve spontaneously. Hematuria usually stops after a few days and does not necessitate any treatment. Mild urothelial hyperplasia in the stent lumen is common but usually regresses after 4 to 6 weeks. Many authors suggest the use of a double-pigtail catheter for the first 4 to 6 weeks to avoid narrowing of the ureteral lumen. The influence of stents on ureteral peristalsis is a major but poorly documented issue. Encrustation is a significant problem that needs to be addressed. The characteristics of both the patient and the stent influence its likelihood. Migration of coated metal stents was seen in 81% of patients at our center. Virtual endoscopy has recently been introduced as a tool for the follow-up of patients with stented ureters. Further design development is necessary to obtain the ideal ureteral metal stent. In a recent study in female pigs, paclitaxel-eluting metal stents engendered less inflammation and hyperplasia of the surrounding tissues.