Impaired bone metabolism following augmentation cystoplasties in growing rats

Animal models in urinary diversion

We set out to critically assess the value of animal experimentation in urinary diversion through intestinal segments, as some authors question the effectiveness of animal research, criticising the methodological quality, lack of standardization, inadequate reporting and the few systematic reviews in this field. Based on a comprehensive MEDLINE literature search (MeSH database; search terms: urinary diversion, urinary reservoirs, continent, rat, dog, animal models) we retrieved and evaluated all full-length papers published in English, German, French, and Spanish languages from 1966 to 2011 reporting the use of animal models in the setting of urinary diversion. Studies were stratified according to the addressed research question. Within each category species, gender, number of animals, age at procedure, type of diversion, mortality, length of follow-up, experimental procedure and outcome were recorded and tabulated. In all, 159 articles were judged to be relevant and while there are numerous animal models only a few have been used in more than one study. Animals were used for the systematic study of new surgical techniques (93 articles) or metabolic and functional consequences of urinary reconstruction (66 articles). For the latter purpose, the most often used animal is the rat, whereas the dog model is preferred for technical experimentation. In many studies, the validity of the model is at least questionable. Animal experiments have repeatedly been conducted addressing the same question, often with striking discrepancies in outcome. Animal studies were even performed after a surgical technique had been pioneered in humans. The use of animal models in urinary diversion is far from standardized rendering the results less than ideal for comparison across studies. Due to differences in anatomy and physiology, the applicability of findings in animal experiments to clinical urology is limited. Continued effort is needed to optimise the use of animal models in experimental urology.

Evaluation of bone mineral density after ileocystoplasty in children with and without myelomeningocele

We evaluated the bone mineral density (BMD) after ileal augmentation cystoplasty in a group of children with and without myelomeningocele. Between 1996 and 2003, eight patients with neurogenic bladder and seven patients with non-neurogenic bladder underwent augmentation ileocystoplasty. Preoperative and postoperative serum creatinine and electrolytes were measured. All patients underwent clinical evaluation, supine height measurement, blood gas analysis, and BMD measurement using a dual energy X-ray absorptiometry (DEXA) postoperatively. BMD was measured at L1-L4 and femoral neck, and compared to age- and sex-matched population. Follow-up time was calculated from the day of surgery to the day of DEXA performance. A total of eight boys and seven girls with the mean age of 10.2 +/- 4.1 years were evaluated with respect to BMD measurement. Mean age was 9.8 years in neurogenic group and 10.5 in non-neurogenic group. Mean follow-up was 728 and 616 days in neurogenic and non-neurogenic groups, respectively. There were no significant differences between ages, follow-up times, preoperative and postoperative creatinine levels, pH and bicarbonate values, and supine heights. Mean BMD at L1-L4 was 55.7% in neurogenic group and 83.8% in non-neurogenic group. There was a statistically significant difference between the two groups (P = 0.02). Mean BMD at femoral neck was 72% in neurogenic group and 86.2% in non-neurogenic group. The difference was also statistically significant (P = 0.028). After augmentation ileocystoplasty, the BMD in early postoperative period of patients with myelomeningocele is lower than the patients with non-neurogenic neurogenic bladder, which have the same clinical characteristics except the neurologic pathology. In the light of our findings and the reported literature data as well, we may claim that BMD decrease after augmentation ileocystoplasty depends more on the underlying neurologic pathology and its locomotor consequences rather than the enterocystoplasty itself.

Changes in bone structure after augmentation cystoplasty in chronic uraemic rats

OBJECTIVE

To investigate the effect of urinary diversion using several types of intestinal segments on cortical and cancellous bone structure of growing rats with renal insufficiency.

MATERIAL AND METHODS

In all, 110 female Sprague-Dawley rats (8 weeks old) had either a two-stage subtotal nephrectomy by removing five-sixths of the renal mass, or a sham operation. Except for a uraemic control group, all uraemic rats then had an enterocystoplasty using stomach, ileum or colon (20 animals per group). An additional group with colic augmentation received the bisphosphonate ibandronate. After 12 weeks, the left tibia was assessed using peripheral quantitative computed tomography and bone histomorphometry.

RESULTS

After subtotal nephrectomy all groups had approximately 30% less endogenous creatinine clearance. Renal failure alone or in association with gastric or colic augmentation induced only negligible changes in the mass and structure of cortical and cancellous tibial bone. In contrast, rats after ileal augmentation and renal failure had a significant reduction in cancellous bone mineral density (P < 0.05) whereas the reduction in trabecular bone area and volume was not statistically significant. Furthermore, ileocystoplasty caused a decrease in trabecular number and perimeter, increased trabecular separation and enlarged bone marrow space, whereas ileocystoplasty had no effect on cortical bone. The changes were not associated with alterations in serum pH. Ibandronate treatment in the colonic cystoplasty group increased trabecular bone mass and structural variables over the untreated colonic cystoplasty group.

CONCLUSIONS

These results suggest that cystoplasty using an ileal segment causes a decrease in bone mass and architecture in growing rats with mild uraemia. It remains open to question whether the results obtained from experimental animals can be directly extrapolated to the clinical situation.

Bladder, bowel and bones--skeletal changes after intestinal urinary diversion

Impaired bone metabolism following urinary diversion through intestinal segments has always been a controversial subject of unclear clinical relevance. Whereas the perpetuated pathophysiological considerations seem conclusive in theory, the role of acidosis and malabsorption is less clear in animal experimentation and, even more so, in the clinical reality of modern continent diversion. In hardly any of the available contemporary case series was overt derangement of the acid-base balance, rickets or osteomalacia encountered. No consistent changes in osteotropic serum parameters could be found with normal calcium and phosphate in all patients. The assumption that colonic reservoirs have a higher risk of developing metabolic bone disease could not be confirmed by clinical data. As early correction of base excess is easy and probably a common policy in patients with intestinal urinary reservoirs, it will be virtually impossible to further study the natural history of bone metabolism after urinary diversion. While there is no need for a bone specific follow-up in asymptomatic adults with a normal acid-base balance, particular attention should be paid to children and to all patients with impaired renal function.

Effect of Augmentation Cystoplasty on Bone Metabolism in Chronic Uremic Rats

PURPOSE

We examined the impact of urinary diversion using several types of intestinal segments on the bone metabolism of growing rats with renal insufficiency.

MATERIALS AND METHODS

A total of 110, 8-week-old Sprague-Dawley rats underwent 2-stage subtotal nephrectomy by removal of 5/6 of the renal mass or sham operation. Except for a uremic control group all uremic rats underwent enterocystoplasty using stomach, ileum or colon. An additional group with colic augmentation received the bisphosphonate ibandronate. Bone mineral density of the tibia and lumbar spine, serum analysis and urinary excretion of the bone resorption marker deoxypyridinoline were determined monthly for 12 weeks. At study termination bone ash weight, bone mineral analysis and serum osteotropic hormone levels were determined.

RESULTS

All groups undergoing subtotal nephrectomy had a decreased endogenous creatinine clearance of approximately 30%. The lowest gains in tibial and lumbar spine bone mineral density were observed in animals undergoing ileocystoplasty. Femoral calcium content was significantly decreased in uremic ileocystoplasty rats compared with uremic controls. These changes were not induced by alterations in serum pH, nor were they associated with accelerated bone resorption as assessed by deoxypyridinoline. Ibandronate prevented changes related to bone resorption and increased bone mass.

CONCLUSIONS

Our results suggest that cystoplasty using ileum segments can aggravate renal bone disease in growing rats with mild uremia. Since the acid-base state was unchanged, other properties of the interposed ileum segment must be responsible for the negative effect on bone metabolism.

The effect of enterocystoplasty on bone strength assessed at four different skeletal sites in a rat model

The objective of the study was to investigate bone strength at four different skeletal sites in a chronic animal model of urinary diversion. Young male Wistar rats (120) were allocated randomly to four groups undergoing ileocystoplasty; ileocystoplasty and resection of the ileocecal segment; colocystoplasty; or sham operation (controls). After 8 months the lumbar vertebrae, femora, and tibiae were harvested at necropsy. Bone strength was assessed biomechanically at four different skeletal sites: vertebra L3, femoral middiaphysis, femoral neck, and distal femoral metaphysis. Bone mass and architecture were assessed using standard static histomorphometry of the proximal tibial metaphysis (trabecular bone volume [BV/TV]; trabecular number [Tb.N]) and ash weight. Statistically significant differences of biomechanical parameters between groups were observed at three skeletal sites with corresponding changes in tibial histomorphometry. Isolated ileocystoplasty resulted in decreased maximum load values of L3 (-16.4%; p < 0.0035) and a substantial reduction in tibial BV/TV (-34.7%; p < 0.05). Ileocystoplasty combined with resection of the ileocecal segment led to a significant loss of bone strength of L3 (-32.4%; p < 0.0015) and a dramatic reduction of tibial BV/TV (-45.9%; p < 0.01). Loss of tibial metaphyseal bone mass was predominantly caused by a decrease in Tb.N. (p < 0.01). Colonic augmentation had no significant effect on bone strength or histomorphometric values. In conclusion, this is the first experimental study to demonstrate the relevance of histomorphometrically proven bone loss after enterocystoplasty in terms of biomechanical variables.

Metabolic findings after colocystoplasty in children

OBJECTIVES

To investigate whether colocystoplasty has resulted in metabolic changes in the growing child during long-term follow-up according to whether cecum with ascending or sigmoid colon was used.

METHODS

Twenty-eight patients (mean age at surgery 11 years) were included in the study and divided into two groups: group 1, cystoplasty with cecum and ascending colon (12 patients) and group 2, sigmoid cystoplasty (16 patients). Patients' linear growth, body mass index, and the following parameters were estimated before surgery and at 3, 6, and 12 months, and then yearly after surgery: blood and urine electrolytes (sodium, potassium, chloride, calcium, phosphorus, magnesium), creatinine, urea, blood gases, blood pH, urine pH, and blood alkaline phosphatase (ALP). All the data were statistically analyzed.

RESULTS

In group 1, the blood ALP increased significantly (P = 0.026) during follow-up. Severe metabolic acidosis with or without hyperchloremia was found in 7 patients. In group 2, the serum sodium and serum calcium levels decreased significantly (P = 0.014 and P = 0.003, respectively); however, the blood ALP, urine sodium, and urine phosphorus levels increased significantly (P = 0.033, P = 0.027, and P = 0.026, respectively) during follow-up. A statistically significant decrease in blood pH (P = 0.022) was found after surgery. Severe metabolic acidosis with or without hyperchloremia was detected in 5 patients. The average linear growth decreased significantly (P = 0.001 and P = 0.016, respectively) 1 and 2 years postoperatively.

CONCLUSIONS

The statistically significant increase in blood ALP and decrease in serum calcium indicate bone demineralization after colocystoplasty. Our investigations in children suggest that bone demineralization is more frequent after sigmoid cystoplasty than after the use of cecum and ascending colon.

Skeletal growth and long-term bone turnover after enterocystoplasty in a chronic rat model

OBJECTIVE

To investigate skeletal growth and bone metabolism in a chronic animal model of urinary diversion.

MATERIALS AND METHODS

Young male Wistar rats (120) were allocated randomly to four groups undergoing: ileocystoplasty, ileocystoplasty and resection of the ileocaecal segment, colocystoplasty, and controls. All animals received antibiotics for 1 week after surgery; half of each group remained on oral antibiotics. Bone-related biochemistry was measured in serum and urine. Dual-energy X-ray absorptiometry and peripheral quantitative computed tomography (pQCT) were used to determine bone mass ex vivo.

RESULTS

Most (90%) of the rats survived the study period (8 months); six rats died from bowel obstruction at the level of the entero-anastomosis and four had to be killed because of persistent severe diarrhoea. Vital intestinal mucosa was found in all augmented bladders. There were no differences in bone length and volume. Loss of bone mass was almost exclusively in rats with ileocystoplasty and resection of the ileocaecal segment (-37.5%, pQCT, P < 0.01). There was no hyperchloraemic metabolic acidosis or gross impairment of renal function. Hypomagnesaemia, hypocalcaemia and decreased insulin-like growth factor-binding protein 3 were the only significant findings on blood analysis. Deoxypyridinoline crosslinks in urine were higher in rats with an enterocystoplasty than in controls.

CONCLUSIONS

Enterocystoplasty in rats neither impairs skeletal growth nor bone quantity, but leads to significant loss of bone mass when combined with resection of the ileocaecal segment. Rarefaction of the trabecular network is confined to the metabolically highly active cancellous compartment, most likely as a consequence of intestinal malabsorption.

Bladder reconstruction: urothelial augmentation, trauma, fistula

Urothelial augmentation in the form of augmentation enterocystoplasty continues to be the mainstay of surgical treatment for neuropathic bladder dysfunction and detrusor instability. The outcome of the procedure is satisfactory, but a number of complications are becoming more clearly defined. Computed tomography cystography is now the investigation of choice for diagnosing bladder rupture. The indications for computed tomography cystography are discussed. The current management of enterovesical fistula is reviewed.

Perimesenteric detubularization of ileum for ileocystoplasty improves compliance and increases capacity

OBJECTIVE

To describe a modified form of detubularization using a perimesenteric incision of the ileal segment, which increases the capacity of the neobladder and reduces the length of the ileal segment required.

PATIENTS AND METHODS

From February 1993 to November 1999, ileocystoplasty was undertaken in 20 patients (mean age 8.4 years, range 4-16). Six had myelodysplasia, four had primary epispadias, five had bladder exstrophy, three had post-traumatic lesions and two had cloacal exstrophy. The patients were divided into two groups; in the first (eight patients, mean age 9.6 years, range 5-15) the ileal segment was opened along the antemesenteric border and in the second (12 patients, mean age 7.7 years, range 4-16) the ileal segment was opened adjacent to the mesentery, perimesenterically. Each segment was then folded and the perimesenteric edges sutured to form the pouch.

RESULTS

The patients were assessed at 1 year after surgery; the neobladder capacity was evaluated as ((neobladder capacity - bladder capacity)/body weight), which shows the relative increase of bladder capacity after enterocystoplasty per unit of weight. There was a statistically significant increase in neobladder capacity in group 2 (perimesenteric transection; Kruskal-Wallis chi-square, P = 0.005; Mann-Whitney U-test, P = 0.006).

CONCLUSION

These results indicate that augmentation can be carried out by perimesenteric transection of the intestinal segment, which improves compliance and increases capacity of the neobladder.