TOTAL ALLOPLASTIC REPLACEMENT OF THE URINARY BLADDER

Bladder cancer is the second most common malignancy of the genitourinary tract. In the United States in 1992, the estimated incidence of carcinoma of the bladder was 50,000 cases. Cystectomy was the treatment of choice in up to 8000 of these patients. 10 Many more cystectomies and urinary diversions were done because of disabling congenital or acquired functional disorders of the bladder including interstitial and radiation cystitis, neurogenic dysfunction, and bladder exstrophy. 13 Currently, these patients undergo various types of intestinal urinary diversion. These procedures represent a marked advancement over bilateral ureterostomies; however, many problems are associated with their use. Ureterosigmoidostomy, perhaps the oldest form of urinary diversion, has an unacceptably high incidence of colon cancer, fecal and urinary incontinence, and metabolic abnormalities. 19 Ileal conduit urinary diversion is the most common form of urinary diversion, but long-term follow-up has revealed upper tract deterioration in 60% of patients. In addition, many patients are plagued with a wide spectrum of stomal problems, metabolic disturbances, stone formation, and mucous production. Reoperation rates are approximately 25%. 12,14 Continent pouches and bladder substitutes have come to the forefront in the last 7 to 10 years. They eliminate the need for an external appliance with continence rates for pouches approaching 100%. Continence rates for neobladders are less (85% to 95%), however, and their use in women is limited because curative cancer surgery necessitates the removal of the entire urethra and external sphincter mechanism. The use of longer segments of bowel creates a greater risk of short bowel syndrome and its sequelae. These include altered bile salt metabolism, vitamin B 12 deficiency, and chronic diarrhea. Mucous production and stone formation continue to plague these patients, and pouch rupture can be disastrous. 8,23 Reoperation rates approach that of conduits (24.5% and 20.4% for pouch and neobladders, respectively). 30 Much research in the last decade has been directed toward the use of gastrointestinal segments as bladder substitutes; however, the aforementioned problems as well as associated physical and psychological complaints 31 should provide the impetus for continued investigation of total alloplastic replacement of the lower urinary tract. Since the development of the first artificial bladder in 1960, features of a successful prosthesis have been identified (Table 1). Therefore, it is necessary to review the evolution of materials and methods used for alloplastic bladder replacement. Various polymers and biodegradable materials have been evaluated for use in replacement of the urinary tract. 17,26 Silicone has proved to be the most suitable. In addition to its biocompatibility, it can withstand prolonged immersion in urine without losing its flexibility, shape, or durability. 27 Furthermore, encrustation studies have shown silicone to be the most resistant to mineral deposition. 17,28 Silicone is not the ideal material for bladder substitution, however, because it is not always resistant to infection. The first artificial bladder was made in 1960 by Bogash et al. 9 The ureters drained into a silicone tube that exited through the abdominal wall. Hydronephrosis and urinary infection ensued and none of the recipients lived more than 4 weeks. To fulfill the function of adequate storage volume without increased intravesical pressures, thin-walled collapsible bladders with volumes ranging from 200 to 600 mL were designed by Friedman et al 15 and several other groups. 1,2,4,10 Thick fibrous capsules formed around the prosthesis, however, leading to capsular contraction that interfered with expansion and emptying. Filling pressures were increased secondary to adynamic obstruction and hydronephrosis and renal failure followed. Residual urine and periurethral leaks were also common and contributed to significant infection rates. Abbou et al 1,2 developed a 600-mL silicone bladder equipped with antireflux valves and a balloon urethral sphincter. It had pleated sides designed to facilitate complete emptying, but the aforementioned problems continued to occur soon after implantation. Barrett and Donovan 5 developed a semirigid-walled ovoid bladder with modification of the sphincter and ureteral anastomoses (Fig. 1). Theoretically, this design would maintain its shape under the compressive forces of a fibrous capsule, yet remain flexible enough to be drained by gravity. Problematic emptying and filling again led to recurring problems of infection and hydronephrosis. Kline et al 21 and Belden et al 7 designed bladders with a combination of rigid bases and flexible tops. They functioned well initially but similar problems were expected with longer follow-up. In the late 1970s, Bordat 10 and Apoil et al 4 designed bistable bladders; they are stable in both full and collapsed positions. Some energy was required to initiate emptying and re-expansion. Stored energy within the bladder's shape completed the cycle once it had begun. This type of prosthesis was experimentally implanted in 40 dogs, with the longest survival rate of 16 months. Early reports demonstrated better compliance curves and greater re-expansion than semirigid models, but ultimately failure was again secondary to hydronephrosis, urethral leaks, and renal failure. Gleeson et al 16 and Rigotti et al 29 devised fixed-volume reservoirs that would not be affected by compressive forces generated by fibrous capsular formation. Therefore, ureteric pressure needed to propel urine into the bladder, as well as the risks of hydronephrosis and renal failure, would be lessened. Emptying and filling of the reservoir, however, depended on volume displacement by air entry and exit from an external connection. Good results were achieved during 1- to 3-months follow-up, but potential periprosthetic infection and unfavorable cosmetic results were disadvantages. Lutzeyer and co-workers 22 developed a single-chamber silicone bladder that rebounded to its original configuration after external compression. It was implanted in 13 sheep and worked well in approximately 50% for a mean of 7 months. This prosthesis has limited use in humans, however, because it requires subcutaneous implantation and manual compression for emptying.