Urothelial dysplasia of the bladder: diagnostic features and clinical significance.

The 2004 World Health Organization classification system for urothelial neoplasia identifies urothelial dysplasia (low-grade intraurothelial neoplasia) as a premalignant lesion of the urothelium. Although diagnostic criteria of urothelial dysplasia have been improved in recent years, there is a frequent lack of interobserver reproducibility. Follow-up studies suggest that dysplasia is a marker for urothelial instability and disease progression in up to 19% of patients, thus supporting an active clinical follow-up in these patients. The main differential diagnosis of urothelial dysplasia includes flat urothelial lesions with atypia, mainly flat (simple) urothelial hyperplasia, reactive urothelial atypia, urothelial atypia of unknown significance, and urothelial carcinoma in situ (high-grade intraurothelial neoplasia). In most cases, morphologic features alone suffice for diagnosis. Some cases may require a panel of immunohistochemical antibodies consisting of cytokeratin 20, p53 and CD44 for diagnosis. We present pathologic features and clinical significance of urothelial dysplasia with emphasis on differential diagnosis from common flat urothelial lesions with atypia.