Struvite urolithiasis and chronic urinary tract infection in a murine model of urinary diversion.

OBJECTIVE To characterize the clinical course after cutaneous vesicostomy (CV) in megabladder (mgb(-/-)) mice with functional urinary bladder obstruction. MATERIALS AND METHODS A total of 45 mgb(-/-) male mice underwent CV at a median age of 25 days. The 34 mice that survived >3 days after CV were evaluated by serial observation and renal ultrasonography. The moribund mice were killed. The urinary bladders and kidneys were analyzed by histopathologic analysis, and urine biochemical studies were performed. RESULTS At a median duration of 11 weeks after CV, 35% of mgb(-/-) male mice (12 of 34) had become moribund with pelvic masses, which were identified as bladder stones at necropsy. The urine pH was alkaline, and microscopic examination demonstrated struvite crystals. The urine samples contained Gram-positive cocci, and the urine cultures were polymicrobial. The stone composition was chiefly struvite (88%-94%) admixed with calcium phosphate. In 40% of cases (2 of 5), retained intravesical polypropylene suture was identified as the presumed nidus. No stones were detected in >100 male mice before CV or in 25 cases when CV was performed using polydioxanone suture. The kidneys from 33% of the mice (4/12) with bladder stones contained staghorn calculi. The histopathologic findings from the mice with struvite stones demonstrated active cystitis, pyelitis, and chronic pyelonephritis. CONCLUSION These findings attest to the importance of the nidus in lithogenesis and provide a novel murine model for struvite urolithiasis and chronic infection of the diverted urinary tract. UROLOGY 81: 943-948, 2013. (C) 2013 Elsevier Inc.