Purpose: Enterocystoplasty provides needed improvement in bladder storage parameters in many patients but it also generates significant morbidity. We evaluated the unusual potential alternative of using the capsule that forms around a standard silicone tissue expander placed perivesically to augment the bladder in dogs.
Materials and methods: Six mongrel dogs underwent baseline videourodynamics and assessment of serum electrolytes, followed by placement of a 250 to 500 cc perivesical silicone tissue expander. Four months after implantation the tissue expander was removed and the fibrous capsule around the expander was biopsied. The capsule was opened and anastomosed to the bladder to augment storage. Serum electrolytes were determined 2 and 4 weeks after augmentation. Videourodynamics were repeated after 3 to 5 months, that is at sacrifice. The harvested bladders underwent histological evaluation.
Results: Five dogs underwent augmentation as described, while in an additional dog that underwent intraperitoneal placement of the tissue expander a fibrous capsule failed to form. Of the 5 augmented dogs 4 underwent repeat urodynamic and electrolyte evaluation with harvesting of the lower urinary tract, while 1 died of undetermined causes 3 weeks after augmentation. A distinct capsule formed in all dogs and augmentation was technically achievable. Anastomosis calcification in 3 dogs limited filling the augmenting capsule for cystography. Bladder capacity and compliance improved in all animals but it varied in degree. Histological examination of the capsule biopsies showed collagen rich connective tissue without epithelium or smooth muscle. After augmentation the capsular segment revealed urothelium in all cases with squamous metaplasia in 1. The subepithelial region had dense fibrosis and a thin band of osseous metaplasia occupied the lamina propria in all cases. Disorganized smooth muscle bundles were noted in all augmented bladders within the collagen of the capsule wall.
Conclusions: Bladder augmentation with the collagenous capsule formed over a perivesical tissue expander is technically feasible. There was evidence of epithelial and smooth muscle ingrowth from the native bladder with improved bladder capacity and compliance in all dogs. Osseous metaplasia of the luminal surface of the collagen based capsule that developed in all animals may have been responsible for anastomotic narrowing and limited filling on cystography.