Urothelial hyperplasia with calculi (papillomatosis) in the urinary bladder of a male spontaneous diabetic Torii rat

Abstract

A 40-week-old male spontaneous diabetic Torii rat, an animal model of type 2 diabetes mellitus, was found to have marked urinary calculi with hematuria in the urinary bladder on necropsy. Histological findings in the urinary bladder included a papillary growth pattern with a fibrovascular stroma without atypia. Fine granular materials in the bladder lumen were positive for Von Kossa staining but negative for periodic acid-Schiff or Gram staining, indicating no apparent bacterial infection in the urinary bladder. Scanning electron microscopy revealed that the urinary calculi were magnesium ammonium phosphate crystals (struvite). On the basis of the results, the lesion was diagnosed as urothelial hyperplasia with calculi (papillomatosis). Chronic inciting stimuli by struvite crystals were considered the primary cause of the bladder findings. (Key words: the spontaneously diabetic Torii rat, urothelial hyperplasia, urinary calculus, papillomatosis Fig. 3. Scanning electron microscopy of uroliths and the bladder surface. (A) Urinary calculi composed of aggregates of polygonal microcrystals from 100 µm to 200 µm in length. (B) Surface irregularities and roughness were detected, whereas ulcers and bacteria were not.