Nephrogenic metaplasia of the ureter.

We present what, to our knowledge, is the first reported case of nephrogenic metaplasia of the ureter. Nephrogenic metaplasia involves the transitional epithelium of the urinary tract and results in the formation of epithelial tubules, which are histologically similar to renal tubules. Special stains demonstrated both intracellular and intraluminal mucin. Ultrastructurally, the lesion consisted of epithelial cells with sparse microvilli and a thick basal lamina. The criteria for diagnosis and differentiation from carcinoma are discussed.