Unilateral renal dysplasia was found in a male Std: Syrian hamster at 13 weeks of age. At necropsy, the kidney was markedly reduced in size (0.1539 g), and had a granular surface and pale color. The kidney had renal papillae. Histologically, the kidney had a distinct cortico-medullary junction. In the cortex, small glomeruli, poorly differentiated tubular epithelia, and flattened tubular epithelia were observed. The poorly differentiated epithelia were single-or multi-layered, and had nuclei of

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... varying size and shape, i.e. round, oval or kidney-shaped. They were described as having moth-eaten basement membranes. In the medulla, flattened tubular epithelia were observed. Ultrastructurally, the small glomeruli were composed of well-differentiated cells, therefore they may not have been primitive, but rather immature. The poorly differentiated epithelia did not have lumina or brush borders, and were concluded to be primitive tissues. This case was characterized by immature glomeruli and primitive cortical tubular epithelia, and likely represents a developmental disorder. In conclusion, this case was diagnosed as renal dysplasia, but the histological features did not resemble those of human renal dysplasia. (J Toxicol Pathol 2001; 14: 309-312)