0022-5347 /92/1482-0281$03.00/0 VcL 148 281-284,
THE JOURNAL OP UROLOGY
1
Printed
Copyright© 1992 by AMERICAN UROLOGICAL ASSOCIATION, INC.
1992
US.A.
METALLIC WALLSTENTS: A NEW THERAPY FOR EXTRINSIC URETERAL OBSTRUCTION WALTER PAUER
AND
HERBERT LUGMAYR
From the Departments of Urology and Radiology I, General Hospital, Weis, Austria
ABSTRACT
Self-expanding metallic stents, frequently used in interventional radiology, were implanted into 15 obstructed ureters in 12 patients. The cause of obstruction was lymph node metastases of different malignant tumors or direct tumor compression of the ureter. Followup in 12 patients was 3 to 31 weeks. Immediately after implantation all stents drained well. During the initial 4 weeks slight obstruction occurred due to hyperplasia of regenerating urothelium. The stents were fully incorporated into the ureteral wall 8 weeks after implantation, they were covered by smooth epithelium and the hyperplasia had disappeared. Complications were hemorrhagia in 1 patient and incrustation in 2. No infection was observed. Complications due to the tumor were obstruction distal to the stent in the presence of a widely open catheter in 3 patients. Early results are presented. Late results are not yet available. The method seems to be minimally invasive and easy to perform. KEY WORDS:
ureter, urinary catheterization, ureteral obstruction, carcinoma
Percutaneous nephrostomy and Double-J* stents are frequently used for relief of extrinsic ureteral obstruction in patients with metastatic carcinoma. As shown in the literature more than 45% of all Double-J stents do not solve the problem because obstruction recurs within the first 30 days. 1 On the other hand, the alternatively performed percutaneous nephrostomy is affected with serious complications, such as hemorrhage and infection, in approximately 4 to 5% of the patients. 2• 3 The self-expanding metallic catheter (Wallstentt) offers the possibility to restore physiological flow inside the ureter without the risk of recurrent obstruction, hemorrhage or infection. Implantation is easy and minimally invasive. MATERIALS AND METHODS
Between April 1980 and June 1991, 12 patients (15 ureters) with multiple metastases from malignant tumors and ureteral extrinsic obstruction with marked hydronephrosis were treated by endoscopic implantation of a self-expanding stent. Patient age and sex, diagnosis, site and cause of obstruction, date of implantation, followup and complications are listed in the table. Only patients who met the following criteria were selected for implantation: current polychemotherapy, life expectancy of at least 6 months, nonfunctioning Double-J stent or nephrostomy tube, severe clinical symptoms associated with hydronephrosis or increasing serum creatinine level. A total of 9 patients underwent polychemotherapy at implantation, while 2 with stage T3,N2,MO- l carcinoma of the prostate previously underwent orchiectomy and estramustine phosphate therapy, and 1 had polychemotherapy and radiation for transitional cell carcinoma of the bladder. Three patients presented with severe colicky pain, 3 with septic fever and 1 with anuria. The serum creatinine level was significantly elevated in 6 patients. The device used was woven from multiple strands of a medical grade stainless steel alloy as used in interventional radiology for vascular distention (fig. 1). The woven structure allows for extreme flexibility. The stent is inserted in a stretched position. After being distended by a releasing mechanism the stent increases in diameter (maximum 7 mm.) while decreasing the length. The inserting mechanism then can be retracted easily while the stent remains in place. The morphology of the stent and the releasing technique have been described previously. 4 - 9 Accepted for publication January 31, 1992. * Medical Engineering Corp., New York, New York. t Medinvent SA, Lausanne, Switzerland.
Technique of implantation. The ureteral obstruction is localized under fluoroscopic vision, and its site and length are marked on the monitor. Care must be taken not to move the patient or the C-arm after the obstruction is marked. A guide wire is inserted through a 6F cobra catheter and pushed up through the stenosis. With the wire as a guide, an Olbert ballooii dilator is inserted and the stenosis is dilated with 10 bar intraluminal pressure. After the balloon dilator is removed insertion of the self-expanding stent is easy along the guide wire. The stent is mounted on a catheter in a stretched manner and covered by a plastic sheath. Under fluoroscopic control the stent is placed exactly inside the stricture. One must ensure that the stent exceeds both ends of the obstruction because when it is released by removal of the outer sheath the stent gains diameter and loses length. If it becomes evident that the stricture is longer than the implanted stent, a second selfexpanding stent may be placed easily in an overlapping manner. Sometimes, it is necessary to dilate again after implantation of the stent to ensure that it is expanded fully and there is no free space between the stent and ureteral wall. If it is not possible to pass a guide wire through the stricture from below it, the same procedure is also possible via a nanh~r.c,t.-,,m» tract. Placement of a self-expanding stent in a is shown in figure 2. To date we were able to bypass all obstructions endoscopic manipulation. After implantation of the stent a Double-J catheter was inserted in all patients and this was removed 4 weeks later. Norfloxacin as perioperative prophylaxis was administered for 10 days. AH patients were followed every 4 weeks with urine cultures, sonography of both kidneys, determination of serum creatinine levels (once a month) and excretory urography (IVP) (after 2 and 6 months). If necessary, isotope studies using the furosemide washout technique were performed. RESULTS
Average followup was 27 weeks (range 3 to 53). Of 15 stents 13 remained open during the observation period. In 2 patients we observed incrustations of the stent after 30 weeks. Endoscopic examination revealed incrustations in a small area of the stent that was not covered by urothelium because it did not contact the ureteral wall in this area. Incrustations could be removed endoscopically. Contrast medium administered via a ureteral catheter immediately after implantation of the stent easily passed down the ureter through the stenotic area and into the bladder. 281
282
PAUER AND LUGMAYR
Pt. No.-Age-Sex
Date of Implantation
Results in 12 patients Diagnosis
Followup
Cause of Obstruction
Event
1-F -29
Malignant melanoma
Feb. 26, 1990
5 mos.
2-F
Ca of colon
June 13, 1990
7 mos.
3-F -76
Ca of bladder
Nov. 20, 1990
12 mos.
Rt. stricture (after radiation), It. tu-
4-F -67 5-F -74
Ca of ovaries NonHodgkin's lymphoma
Nov. 20, 1990 Dec. 3, 1990
12 mos. 12 mos.
Tumor compression Lymph node metastases
Hematuria Incrustion endoscopically removed Apr. 19, 1991
Ca of breast
Dec. 22, 1990
-11-mos.
Lymph node metas-
Tumor -progression,
-46
Lymph node metastases Lymph node metastases
Died July 19 Incrustation It. side, removed endoscopically Dec. 7, died Jan. 24, 1991
mor compression
6-F
-65
tases
7-M -59
Ca of sigmoid
Jan. 10, 1991
6 mos.
8-M -61
Ca of prostate
Jan. 15, 1991
5 mos.
9-F
-63
Ca of endometrium
Feb. 5, 1991
3 wks.
10-M -60 11-F -63
Ca of prostate Ca of ovaries
Feb. 22, 1991 Apr. 18, 1991
2 mos. 7 mos.
12-F -59
Ca of ovaries
May 7, 1991
6mos.
Lymph node metastases Tumor compression
Lymph node metastases Tumor compression Lymph node metastases Lymph node metastases
obstruction distal to stent, second overlapping stent implanted Aug. 2, 1991 Hematuria Tumor progression, obstruction distal to stent, second overlapping stent implanted Apr. 19, died June 14 Died Feb. 25 Died July 26
The site of obstruction was the mid ureter on the right side in patients 1, 4, 9 and 12, the left side in patients 5 and 7, and bilaterally in patients 2 and 11. Patient 3 had bilateral intramural ureteral obstruction. Patient 6 had right upper and prevesical ureteral obstruction, while patient 8 had right and patient 10 had left prevesical obstruction. Placement of the stent was antegrade in patients 1, 6 and 10, and retrograde in patients 2 to 5, 7 to 9, 11 and 12.
Macroscopic hematuria occurred in 1 patient but it stopped spontaneously 1 day later. DISCUSSION
FIG. 1. Self-expanding metallic stent (length 45 mm., diameter 7 mm.).
Endoscopic controls with a flexible ureteroscope in patients 1 to 5 revealed smooth, sometimes hyperplastic urothelium that covered the stent completely within 8 weeks. During the initial 4 weeks hyperplasia and edema of the regenerating urothelium were noted in every case. This hyperplasia diminishes with time 10 and can be overcome during the first month by additional insertion of a Double-J stent. Elevated serum creatinine levels returned to normal in all but 1 patient who already had serious parenchymal damage. Urinary tract infection was not observed in any patient. Two patients required secondary overlapping implantation of a self-expanding stent because of tumor progression that compressed the ureter distal to the stent. In 1 patient (malignant melanoma) the ureter was dislocated in such a manner that the ureteral wall occluded the distal opening of the stent, forming a 90-degree angle to the stent. In this patient a silicone Double-J stent restored free urinary flow until the patient died. In 3 patients the stent lumen itself remained open and the obstruction occurred distal to the stent.
Ureteral obstruction by progressive tumor in patients who are not able to undergo surgery for any reason is a problem that has not been solved sufficiently to date. Double-J stents and percutaneous nephrostomy tubes have a high rate of complications (4 to 45%), such as hemorrhage, infection and loss of function due to stent failure. 1•3 Ureteral self-expanding stents offer the possibility to treat such cases of obstruction in a minimally invasive and maximally effective manner. Although most reported uses of expandable metallic stents have been in the vascular system, 4 - 6 they also have been placed in the biliary system and in the penile and prostatic urethra. 7•8 As shown previously, the stent is covered by urothelium within a certain intervaI. 7- 9 In our series we observed complete coverage within 8 weeks. Milroy et al described a coverage period of 4 to 6 months in the penile urethra of dogs. 7 Transitional cell epithelium regenerates more rapidly, and a 4 cm. defect affecting half of the circumference of the ureter will have a new mucosa! surface within 10 days. 10 Wishnow et al described regeneration of the epithelium in experimental denuded bladders. 11 In their experiment the entire bladder (in dogs) was covered by new urothelium within 3 weeks. The regenerated epithelium was described as a hyperplastic transitional epithelium characterized by increased thickness, cells with enlarged nuclei and prominent mitotic activity. During a 9-week period the epithelium gradually returned to a normal appearance. The hyperplastic epithelium, which also was observed in our series, was bridged by insertion of a Double-J stent for the first 4 weeks. The self-expanding stent becomes totally incorporated into the ureteral wall, thus, reducing its potential to act as a nidus for incrustation. No information is available on the long-term
W ALLSTENTS IN URETERAL OBSTRUCTION
283
FIG. 2. Placement of stent in glass model. A, stent is mounted on special catheter inserted over guide wire. B and C, outer sheath is partially withdrawn and stent expands by itself. D, outer sheath is completely withdrawn, stent is expanded and catheter can easily be removed.
Fm. 3. Patient 4. A, retrograde ureteropyelography shows stricture (arrow), and dilated upper ureter and pelvis. B, IVP 8 weeks after implantation of stent (between arrows) shows no dilatation of upper tract.
effects of metallic stents in the urinary tract, nor is any information available about the effect on the peristaltic movement of the ureter after using such a stent. The Whitaker test, performed in 1 of our patients, showed no increased pressure
in the pelvis or upper ureter. When Djurhuus et al studied renal pelvic function after total alloplastic replacement of the ureter in animals, they concluded that ureteral peristalsis was not a prerequisite for normal pelvic function, and the question of
284
PAUER AND LUGMAYR 4, A). This finding can be demonstrated by a simple experiment with elastic material over a rigid tube (fig. 4, B). The rate of nonobstructed stents in our series is higher than the overall survival rate, which suggests the possibility of maintaining lifetime free urinary flow in these patients. REFERENCES
FIG. 4. A, IVP in patient 5 shows disproportion of stent and ureter mimicking stenosis below stent. Note complete coverage of stent with urothelium. B, experimental model demonstrates elastic woven structure (white) over rigid tube (black).
peristalsis occurring in regenerated segments of ureter would be irrelevant. 12 The development of urinary tract infection in the presence of a foreign body was of some concern. However, after initial perioperative antibiotic prophylaxis our patients did not need further antibiotic treatment. The diameter of the stent (7 mm.) used in our series exceeds the diameter of the normal ureter but it seems to be ideal concerning the slight hyperplasia and edema that occur immediately after implantation. After complete incorporation of the stent an ideal lumen results that may be observed on an x-ray, on endoscopy and at autopsy (fig. 3). A diameter of 7 mm. also has the advantage that endoscopy with a diagnostic 9.5F ureteroscope may be done easily. In some patients the disproportion of the self-expanding stent and ureter simulated a stenosis radiographically that was not obstructive urodynamically (fig.
1. Docimo, S. G. and Dewolf, W. C.: High failure rate of indwelling ureteral stents in patients with extrinsic obstruction: experience at 2 institutions. J. Urol., 142: 277, 1989. 2. Stables, D. P.: Percutaneous nephrostomy: techniques, indications, and results. Urol. Clin. N. Amer., 9: 15, 1982. 3. Pfister, R. C. and Newhouse, J. H.: Interventional percutaneous pyeloureteral techniques. II. Percutaneous nephrostomy and other procedures. Rad. Clin. N. Amer., 17: 351, 1979. 4. Gunth~r,IL \Y., Vorw_erk,_ D_._, J3ohndorf, K, el-Dj11, A, Pet_ers, I. and Messmer, B.: Perkutane Implantation von Gefiissendoprothesen (Stents) in Becken- und Oberschenkelarterien. Dtsch. Med. Wschr., 114: 1517, 1989. 5. Duprat, G., Jr., Wright, K. C., Charnsangavej, C., Wallace, S. and Gianturco, C.: Self-expanding metallic stents for small vessels: an experimental evaluation. Radiology, 162: 469, 1987. 6. Gunther, R. W., Vorwerk, D., Bohndorf, K., Peters, I., el-Din, A. and Messmer, B.: Iliac and femoral artery stenoses and occlusions: treatment with intravascular stents. Radiology, 172: 725, 1989. 7. Milroy, E. J. G., Chapple, C.R., Cooper, J.E., Eldin, A., Wallsten, H., Seddon, A. M. and Rowles, P. M.: A new treatment for urethral strictures. Lancet, 1: 1424, 1988. 8. Machan, L., Jager, H. R., Adam, A., Gill, K., Williams, G. and Allison, D. J.: Benign prostatic hypertrophy: treatment with a metallic stent. AJR, 153: 779, 1989. 9. Lugmayr, H. and Pauer, W.: Selbstexpandierende Metall-Stents bei malignen Ureterstenosen. Dtsch. Med. Wschr., 116: 573, 1991. 10. Ramsay, J. W. A. and Whitfield, H. N.: Structure and function of the upper urinary tract. In: Scientific Basis of Urology. Edited by A. R. Mundy. New York: Churchill Livingstone, p. 34, 1987. 11. Wishnow, K. I., Johnson, D. E., Grignon, D. J., Cromeens, D. M. and Ayala, A. G.: Regeneration of the canine urinary bladder mucosa after complete surgical denudation. J. Urol., 141: 1476, 1989. 12. Djurhuus, J. C., Ladefoged, 0. and Jorgensen, S. J.: Renal pelvic function following total alloplastic replacement of ureter in pigs. Electrophysiology, renal function and morphology. Acta Chir. Scand., suppl., 472: 67, 1976.
THE JOURNAL OP UROLOGY
1
Printed
Copyright© 1992 by AMERICAN UROLOGICAL ASSOCIATION, INC.
1992
US.A.
METALLIC WALLSTENTS: A NEW THERAPY FOR EXTRINSIC URETERAL OBSTRUCTION WALTER PAUER
AND
HERBERT LUGMAYR
From the Departments of Urology and Radiology I, General Hospital, Weis, Austria
ABSTRACT
Self-expanding metallic stents, frequently used in interventional radiology, were implanted into 15 obstructed ureters in 12 patients. The cause of obstruction was lymph node metastases of different malignant tumors or direct tumor compression of the ureter. Followup in 12 patients was 3 to 31 weeks. Immediately after implantation all stents drained well. During the initial 4 weeks slight obstruction occurred due to hyperplasia of regenerating urothelium. The stents were fully incorporated into the ureteral wall 8 weeks after implantation, they were covered by smooth epithelium and the hyperplasia had disappeared. Complications were hemorrhagia in 1 patient and incrustation in 2. No infection was observed. Complications due to the tumor were obstruction distal to the stent in the presence of a widely open catheter in 3 patients. Early results are presented. Late results are not yet available. The method seems to be minimally invasive and easy to perform. KEY WORDS:
ureter, urinary catheterization, ureteral obstruction, carcinoma
Percutaneous nephrostomy and Double-J* stents are frequently used for relief of extrinsic ureteral obstruction in patients with metastatic carcinoma. As shown in the literature more than 45% of all Double-J stents do not solve the problem because obstruction recurs within the first 30 days. 1 On the other hand, the alternatively performed percutaneous nephrostomy is affected with serious complications, such as hemorrhage and infection, in approximately 4 to 5% of the patients. 2• 3 The self-expanding metallic catheter (Wallstentt) offers the possibility to restore physiological flow inside the ureter without the risk of recurrent obstruction, hemorrhage or infection. Implantation is easy and minimally invasive. MATERIALS AND METHODS
Between April 1980 and June 1991, 12 patients (15 ureters) with multiple metastases from malignant tumors and ureteral extrinsic obstruction with marked hydronephrosis were treated by endoscopic implantation of a self-expanding stent. Patient age and sex, diagnosis, site and cause of obstruction, date of implantation, followup and complications are listed in the table. Only patients who met the following criteria were selected for implantation: current polychemotherapy, life expectancy of at least 6 months, nonfunctioning Double-J stent or nephrostomy tube, severe clinical symptoms associated with hydronephrosis or increasing serum creatinine level. A total of 9 patients underwent polychemotherapy at implantation, while 2 with stage T3,N2,MO- l carcinoma of the prostate previously underwent orchiectomy and estramustine phosphate therapy, and 1 had polychemotherapy and radiation for transitional cell carcinoma of the bladder. Three patients presented with severe colicky pain, 3 with septic fever and 1 with anuria. The serum creatinine level was significantly elevated in 6 patients. The device used was woven from multiple strands of a medical grade stainless steel alloy as used in interventional radiology for vascular distention (fig. 1). The woven structure allows for extreme flexibility. The stent is inserted in a stretched position. After being distended by a releasing mechanism the stent increases in diameter (maximum 7 mm.) while decreasing the length. The inserting mechanism then can be retracted easily while the stent remains in place. The morphology of the stent and the releasing technique have been described previously. 4 - 9 Accepted for publication January 31, 1992. * Medical Engineering Corp., New York, New York. t Medinvent SA, Lausanne, Switzerland.
Technique of implantation. The ureteral obstruction is localized under fluoroscopic vision, and its site and length are marked on the monitor. Care must be taken not to move the patient or the C-arm after the obstruction is marked. A guide wire is inserted through a 6F cobra catheter and pushed up through the stenosis. With the wire as a guide, an Olbert ballooii dilator is inserted and the stenosis is dilated with 10 bar intraluminal pressure. After the balloon dilator is removed insertion of the self-expanding stent is easy along the guide wire. The stent is mounted on a catheter in a stretched manner and covered by a plastic sheath. Under fluoroscopic control the stent is placed exactly inside the stricture. One must ensure that the stent exceeds both ends of the obstruction because when it is released by removal of the outer sheath the stent gains diameter and loses length. If it becomes evident that the stricture is longer than the implanted stent, a second selfexpanding stent may be placed easily in an overlapping manner. Sometimes, it is necessary to dilate again after implantation of the stent to ensure that it is expanded fully and there is no free space between the stent and ureteral wall. If it is not possible to pass a guide wire through the stricture from below it, the same procedure is also possible via a nanh~r.c,t.-,,m» tract. Placement of a self-expanding stent in a is shown in figure 2. To date we were able to bypass all obstructions endoscopic manipulation. After implantation of the stent a Double-J catheter was inserted in all patients and this was removed 4 weeks later. Norfloxacin as perioperative prophylaxis was administered for 10 days. AH patients were followed every 4 weeks with urine cultures, sonography of both kidneys, determination of serum creatinine levels (once a month) and excretory urography (IVP) (after 2 and 6 months). If necessary, isotope studies using the furosemide washout technique were performed. RESULTS
Average followup was 27 weeks (range 3 to 53). Of 15 stents 13 remained open during the observation period. In 2 patients we observed incrustations of the stent after 30 weeks. Endoscopic examination revealed incrustations in a small area of the stent that was not covered by urothelium because it did not contact the ureteral wall in this area. Incrustations could be removed endoscopically. Contrast medium administered via a ureteral catheter immediately after implantation of the stent easily passed down the ureter through the stenotic area and into the bladder. 281
282
PAUER AND LUGMAYR
Pt. No.-Age-Sex
Date of Implantation
Results in 12 patients Diagnosis
Followup
Cause of Obstruction
Event
1-F -29
Malignant melanoma
Feb. 26, 1990
5 mos.
2-F
Ca of colon
June 13, 1990
7 mos.
3-F -76
Ca of bladder
Nov. 20, 1990
12 mos.
Rt. stricture (after radiation), It. tu-
4-F -67 5-F -74
Ca of ovaries NonHodgkin's lymphoma
Nov. 20, 1990 Dec. 3, 1990
12 mos. 12 mos.
Tumor compression Lymph node metastases
Hematuria Incrustion endoscopically removed Apr. 19, 1991
Ca of breast
Dec. 22, 1990
-11-mos.
Lymph node metas-
Tumor -progression,
-46
Lymph node metastases Lymph node metastases
Died July 19 Incrustation It. side, removed endoscopically Dec. 7, died Jan. 24, 1991
mor compression
6-F
-65
tases
7-M -59
Ca of sigmoid
Jan. 10, 1991
6 mos.
8-M -61
Ca of prostate
Jan. 15, 1991
5 mos.
9-F
-63
Ca of endometrium
Feb. 5, 1991
3 wks.
10-M -60 11-F -63
Ca of prostate Ca of ovaries
Feb. 22, 1991 Apr. 18, 1991
2 mos. 7 mos.
12-F -59
Ca of ovaries
May 7, 1991
6mos.
Lymph node metastases Tumor compression
Lymph node metastases Tumor compression Lymph node metastases Lymph node metastases
obstruction distal to stent, second overlapping stent implanted Aug. 2, 1991 Hematuria Tumor progression, obstruction distal to stent, second overlapping stent implanted Apr. 19, died June 14 Died Feb. 25 Died July 26
The site of obstruction was the mid ureter on the right side in patients 1, 4, 9 and 12, the left side in patients 5 and 7, and bilaterally in patients 2 and 11. Patient 3 had bilateral intramural ureteral obstruction. Patient 6 had right upper and prevesical ureteral obstruction, while patient 8 had right and patient 10 had left prevesical obstruction. Placement of the stent was antegrade in patients 1, 6 and 10, and retrograde in patients 2 to 5, 7 to 9, 11 and 12.
Macroscopic hematuria occurred in 1 patient but it stopped spontaneously 1 day later. DISCUSSION
FIG. 1. Self-expanding metallic stent (length 45 mm., diameter 7 mm.).
Endoscopic controls with a flexible ureteroscope in patients 1 to 5 revealed smooth, sometimes hyperplastic urothelium that covered the stent completely within 8 weeks. During the initial 4 weeks hyperplasia and edema of the regenerating urothelium were noted in every case. This hyperplasia diminishes with time 10 and can be overcome during the first month by additional insertion of a Double-J stent. Elevated serum creatinine levels returned to normal in all but 1 patient who already had serious parenchymal damage. Urinary tract infection was not observed in any patient. Two patients required secondary overlapping implantation of a self-expanding stent because of tumor progression that compressed the ureter distal to the stent. In 1 patient (malignant melanoma) the ureter was dislocated in such a manner that the ureteral wall occluded the distal opening of the stent, forming a 90-degree angle to the stent. In this patient a silicone Double-J stent restored free urinary flow until the patient died. In 3 patients the stent lumen itself remained open and the obstruction occurred distal to the stent.
Ureteral obstruction by progressive tumor in patients who are not able to undergo surgery for any reason is a problem that has not been solved sufficiently to date. Double-J stents and percutaneous nephrostomy tubes have a high rate of complications (4 to 45%), such as hemorrhage, infection and loss of function due to stent failure. 1•3 Ureteral self-expanding stents offer the possibility to treat such cases of obstruction in a minimally invasive and maximally effective manner. Although most reported uses of expandable metallic stents have been in the vascular system, 4 - 6 they also have been placed in the biliary system and in the penile and prostatic urethra. 7•8 As shown previously, the stent is covered by urothelium within a certain intervaI. 7- 9 In our series we observed complete coverage within 8 weeks. Milroy et al described a coverage period of 4 to 6 months in the penile urethra of dogs. 7 Transitional cell epithelium regenerates more rapidly, and a 4 cm. defect affecting half of the circumference of the ureter will have a new mucosa! surface within 10 days. 10 Wishnow et al described regeneration of the epithelium in experimental denuded bladders. 11 In their experiment the entire bladder (in dogs) was covered by new urothelium within 3 weeks. The regenerated epithelium was described as a hyperplastic transitional epithelium characterized by increased thickness, cells with enlarged nuclei and prominent mitotic activity. During a 9-week period the epithelium gradually returned to a normal appearance. The hyperplastic epithelium, which also was observed in our series, was bridged by insertion of a Double-J stent for the first 4 weeks. The self-expanding stent becomes totally incorporated into the ureteral wall, thus, reducing its potential to act as a nidus for incrustation. No information is available on the long-term
W ALLSTENTS IN URETERAL OBSTRUCTION
283
FIG. 2. Placement of stent in glass model. A, stent is mounted on special catheter inserted over guide wire. B and C, outer sheath is partially withdrawn and stent expands by itself. D, outer sheath is completely withdrawn, stent is expanded and catheter can easily be removed.
Fm. 3. Patient 4. A, retrograde ureteropyelography shows stricture (arrow), and dilated upper ureter and pelvis. B, IVP 8 weeks after implantation of stent (between arrows) shows no dilatation of upper tract.
effects of metallic stents in the urinary tract, nor is any information available about the effect on the peristaltic movement of the ureter after using such a stent. The Whitaker test, performed in 1 of our patients, showed no increased pressure
in the pelvis or upper ureter. When Djurhuus et al studied renal pelvic function after total alloplastic replacement of the ureter in animals, they concluded that ureteral peristalsis was not a prerequisite for normal pelvic function, and the question of
284
PAUER AND LUGMAYR 4, A). This finding can be demonstrated by a simple experiment with elastic material over a rigid tube (fig. 4, B). The rate of nonobstructed stents in our series is higher than the overall survival rate, which suggests the possibility of maintaining lifetime free urinary flow in these patients. REFERENCES
FIG. 4. A, IVP in patient 5 shows disproportion of stent and ureter mimicking stenosis below stent. Note complete coverage of stent with urothelium. B, experimental model demonstrates elastic woven structure (white) over rigid tube (black).
peristalsis occurring in regenerated segments of ureter would be irrelevant. 12 The development of urinary tract infection in the presence of a foreign body was of some concern. However, after initial perioperative antibiotic prophylaxis our patients did not need further antibiotic treatment. The diameter of the stent (7 mm.) used in our series exceeds the diameter of the normal ureter but it seems to be ideal concerning the slight hyperplasia and edema that occur immediately after implantation. After complete incorporation of the stent an ideal lumen results that may be observed on an x-ray, on endoscopy and at autopsy (fig. 3). A diameter of 7 mm. also has the advantage that endoscopy with a diagnostic 9.5F ureteroscope may be done easily. In some patients the disproportion of the self-expanding stent and ureter simulated a stenosis radiographically that was not obstructive urodynamically (fig.
1. Docimo, S. G. and Dewolf, W. C.: High failure rate of indwelling ureteral stents in patients with extrinsic obstruction: experience at 2 institutions. J. Urol., 142: 277, 1989. 2. Stables, D. P.: Percutaneous nephrostomy: techniques, indications, and results. Urol. Clin. N. Amer., 9: 15, 1982. 3. Pfister, R. C. and Newhouse, J. H.: Interventional percutaneous pyeloureteral techniques. II. Percutaneous nephrostomy and other procedures. Rad. Clin. N. Amer., 17: 351, 1979. 4. Gunth~r,IL \Y., Vorw_erk,_ D_._, J3ohndorf, K, el-Dj11, A, Pet_ers, I. and Messmer, B.: Perkutane Implantation von Gefiissendoprothesen (Stents) in Becken- und Oberschenkelarterien. Dtsch. Med. Wschr., 114: 1517, 1989. 5. Duprat, G., Jr., Wright, K. C., Charnsangavej, C., Wallace, S. and Gianturco, C.: Self-expanding metallic stents for small vessels: an experimental evaluation. Radiology, 162: 469, 1987. 6. Gunther, R. W., Vorwerk, D., Bohndorf, K., Peters, I., el-Din, A. and Messmer, B.: Iliac and femoral artery stenoses and occlusions: treatment with intravascular stents. Radiology, 172: 725, 1989. 7. Milroy, E. J. G., Chapple, C.R., Cooper, J.E., Eldin, A., Wallsten, H., Seddon, A. M. and Rowles, P. M.: A new treatment for urethral strictures. Lancet, 1: 1424, 1988. 8. Machan, L., Jager, H. R., Adam, A., Gill, K., Williams, G. and Allison, D. J.: Benign prostatic hypertrophy: treatment with a metallic stent. AJR, 153: 779, 1989. 9. Lugmayr, H. and Pauer, W.: Selbstexpandierende Metall-Stents bei malignen Ureterstenosen. Dtsch. Med. Wschr., 116: 573, 1991. 10. Ramsay, J. W. A. and Whitfield, H. N.: Structure and function of the upper urinary tract. In: Scientific Basis of Urology. Edited by A. R. Mundy. New York: Churchill Livingstone, p. 34, 1987. 11. Wishnow, K. I., Johnson, D. E., Grignon, D. J., Cromeens, D. M. and Ayala, A. G.: Regeneration of the canine urinary bladder mucosa after complete surgical denudation. J. Urol., 141: 1476, 1989. 12. Djurhuus, J. C., Ladefoged, 0. and Jorgensen, S. J.: Renal pelvic function following total alloplastic replacement of ureter in pigs. Electrophysiology, renal function and morphology. Acta Chir. Scand., suppl., 472: 67, 1976.
