Upper urinary tract carcinomas: histological types and unusual morphological variants

Carcinomas of the upper urinary tract are, for the most part, of urothelial type and histologically closely resemble their urinary bladder counterparts. However, unlike urinary bladder carcinomas, a high percentage of these tumours correpond to high-grade carcinomas that usually present in advanced clinical stages at the time of initial diagnosis. Another difference between urothelial carcinoma of the upper urinary tract and their urinary bladder counterparts is their tendency to display unusual morphological appearances. The most important differential diagnosis for these tumours is with secondary infiltration of the renal pelvis by renal cell carcinoma, which can also display a wide variety of unusual morphological appearances. This review will describe the spectrum of histological features that can be displayed by urothelial carcinomas of the upper urinary tract with emphasis on their histological differential diagnosis and the role of special techniques for their evaluation.