Stones in Urinary Diversions

Bodo E. Knudsen & Michael W. Sourial

Department of Urology, The Ohio State University Wexner Medical Center, Columbus, OH, USA

Introduction

Urinary diversion using intestinal segments is a widely employed technique in reconstructive urology for the care of urologic patients with both benign and malignant diseases. Applications include pediatric urology, neurogenic bladders, reconstructive urology, and oncology. A wide range of urinary diversions have been described; however, the ileal conduit and the continent orthotopic neobladder are the two of the most commonly performed urinary diversions at present.

Urinary diversions have posed unique challenges to the urologist. Long‐term complications include renal insufficiency, recurrent infections, strictures, metabolic and electrolyte disturbances, secondary malignancies, and calculi. Although modifications and improvements in surgical technique have reduced the risk of complications, postsurgical problems still occur. One such complication is the development of calculi in the diversions. While open surgical management has played an important role in the management of this problem, the advent of endourology and minimally invasive surgical techniques have helped reduce the morbidity from the surgical management of stones in these patients. (See Video 70.1).

Etiology

The etiology of stone formation in patients with urinary intestinal diversion is multifactorial. These can be classified mainly as idiopathic, metabolic, infectious, or structural. It is well known that patients with urinary diversion have metabolic abnormalities due to the reabsorption of urinary solutes across the intestinal mucosa. Hypercalciuria secondary to hyperchloremic metabolic acidosis is a predisposing factor for calcium phosphate stones. In a study by Terai et al., hypocitraturia was observed in over one‐third of patients. An increase in excreted calcium and phosphate coupled with an increase in urine pH created a favorable milieu for infectious calculi [1]. Further, these patients are also often dehydrated, contributing to the process of stone formation.

Patients with urinary diversion are often colonized with urease‐producing bacteria. Common uropathogenic organisms cultured include Proteus, Klebsiella, and Pseudomonas [2], which metabolize urea into ammonium and bicarbonate. The alkaline milieu predisposes to infectious stones, including struvite, carbonate apatite, and ammonium acid urate stones.

Other risk factors for stone formation include excessive mucous production by the intestinal mucosa [3], foreign bodies (staples, nonabsorbable sutures, etc.) acting as a nidus for stone formation, urinary stasis in patients who incompletely empty their reservoirs, or obstruction. Irrigation of the reservoir may be helpful in reducing stone formation by clearing bacterial load and mucous deposits [4–6].

Rates of stone formation

The reported incidence of stones varies depending based on the type of urinary diversion. The incidence of stones is 11–12% in patients with an ileal conduit [7, 8]; 17–43% in patients with a Kock pouch [4, 9, 10]; and 11–19% in patients with an Indiana pouch [10, 11]. Abol‐Enein and Ghoneim [12] published their experience with 450 patients having undergone an orthotopic ileal W‐shaped neobladder with serous‐lined extramural ureteral reimplantation. Their stone incidence rate was 3% [12]. Ferriero et al. reported a rate of neobladder stone formation of 9.2% in 445 consecutive patients who underwent radical cystectomy and a non‐absorbable, titanium stapled orthotopic neobladder [13]. Overall, the incidence of stone formation in patients with urinary diversion seems to be decreasing, due in part to use of absorbable surgical material, and also the heightened awareness of the metabolic and infectious causes of stone formation [14].

The recurrence rate of stones in patients with urinary diversion is common, with reports suggesting rates as high as 50–63% over 5 years [15, 16]. Recurrent urinary tract infection appears to be a risk factor for stone formation [5, 15]. The rate of recurrence seems to be independent of the treatment technique and patient characteristics [16, 17]. Patients with infectious stones may also have recurrences with other non‐infectious type of stones [18].

Types of stones

Patients with urinary diversion are predisposed to infectious stones due to the frequent colonization of the intestinal segment with urease‐producing bacteria. These will hydrolyze urea into the bicarbonate and ammonium. Excess bicarbonate in the urine creates an alkaline urine pH, and leads to the formation of magnesium ammonium phosphate and carbonate apatite stones. Additionally, the hyperchloremic metabolic acidosis state often seen in patients with ileal conduits or colonic reservoirs results in decreased reabsorption of calcium and a decreased production of citrate by the kidneys, favoring calcium stone formation. Calcium oxalate stones are also not infrequently seen in patients with urinary diversion. Hyperoxaluria may be seen in patients when small bowel, especially the terminal ileum, is used for the reconstructive procedure. Resection of the terminal ileum results in an increase in unabsorbed fatty acids and bile salts which undergo saponification by binding with calcium in the bowel. This leads to an increase in unbound oxalate which is absorbed by the large intestine and subsequently excreted in the urine. The resultant hyperoxaluria favors the formation of calcium oxalate stones. In a study by Hertzig et al., the stone composition in 77 patients having undergone a radical cystectomy and ileal conduit was reported. The vast majority (63.5%) were magnesium ammonium phosphate stones, with the remainder being 25% calcium phosphate, 9.6% calcium oxalate monohydrate, and 1.9% calcium oxalate dihydrate [19].

Surgical management

The surgical approach should take into consideration the location and size of the stone and the anatomy of the diversion to plan the access route. Open surgical extraction has been largely replaced by endoscopic and minimally invasive surgical techniques. Modalities such as extracorporeal shock‐wave lithotripsy (ESWL), antegrade and retrograde ureteroscopy, trans‐stomal lithotripsy, percutaneous nephrolithotomy, and percutaneous transreservoir lithotomy have been described in the literature.

Stones in the urinary diversion

Stones in the intestinal diversion may be managed by endoscopic or open techniques. The anatomy of the urinary tract and also the surrounding structures should be outlined with prior radiographic imaging, typically noncontrast computed tomography (CT). Any concomitant strictures should also be delineated and will likely also need to be addressed. Access to the diversion is most easily obtained through the stoma, especially for patients with ileal conduits. In patients with continent reservoirs, care should be taken to avoid traumatizing the continence mechanism. In‐and‐out access through the continence mechanism should only be used for patients with minimal stone burden, with care to avoid excessive manipulation to prevent postoperative leakage or strictures. A flexible cystoscope can usually be safely passed into most diversions, including an Indiana pouch. Olympus produces a flexible cystoscope that has a suction channel. This can be very helpful as it allows the reservoir to be suction‐irrigated, allowing for the clearance of mucus and some debris (see Figure 70.1). In patients with orthotopic reservoirs, access through the urethra with rigid instruments is feasible, although there is a risk of bladder neck contracture. Fragmentation of the stone can be performed with a holmium:YAG laser, ultrasonically, pneumatically/ballistically, or with an electrohydrolic lithotripter. Ultrasonic lithotripters are increasingly being used as they are less harmful to the intestinal mucosa [20].

Image described by caption. — **Figure 70.1** Olympus cystoscope with suction adapter. The adapter fits on the head of the cystoscope and can then be plugged into the usual suction apparatus.

The use of ESWL in patients with a Kock or Indiana pouch has been reported in a small number of patients. These patients should undergo pouchoscopy to ensure the absence of staples or other foreign material acting as a nidus for stone formation. In addition, basketing of fragments is probably necessary to render these patients stone‐free [14, 20, 21].

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