[Non-urothelial tumors of the urinary tract]

Only about 2% of the urinary tract are not of urothelial origin. Our knowledge of their morphology and biology is mainly based on single case reports, and therefore apart from a few exceptions very poor. Generally, the most often affected site is the urinary bladder (79.2%), followed by the urethra (12.7%), pelvis (4.9%) and ureter (3.2%). The urinary bladder also is the only organ in which all different histological types of these tumors were described. According to their histogenesis non-urothelial tumors (NUT) can be classified by the following main groups: soft tissue tumors, mixed epithelial and non epithelial tumors (carcinosarcomas), neuroendocrine carcinomas, carcinoids, malignant lymphomas, malignant melanomas and extragonadal germ cell tumors. Moreover some very interesting tumor-like lesions, like malakoplakia and inflammatory pseudosarcoma, mainly occur in this region. About 75% of all NUT of the urinary tract belong to the soft tissue tumors. Rhabdomyosarcomas in children and leiomyomas and -myosarcomas in adults are the more frequent histological types. Leiomyosarcomas can easily be confused with other tumor types or even with inflammatory pseudotumors. The use of immunohistochemistry to achieve a correct diagnosis is mandatory but not always successful. A relatively frequent tumor occurring in the bladder of young adults is the paraganglioma (pheochromocytoma), which usually produces typical symptoms of catecholamine excess. Carcinosarcomas of the urinary bladder contain both epithelial and mesenchymal components. They have to be distinguished from collision tumors (coexistent but separate carcinoma and sarcoma), spindle cell transitional carcinomas as well as from carcinomas with osseous or cartilaginous metaplasia. Carcinoids and neuroendocrine carcinomas developed from the neuroendocrine cells scattered all over the transitional epithelium of the bladder. Neuroendocrine carcinomas of the bladder are also called "oat cell carcinomas" since they show the same histological features and immunoreactivity as the oat cell carcinomas of the lung. They share also the same poor prognosis. The affection of the urinary tract in generalized malignant lymphomas and leukemias occur in more than 30% of cases. Lymphomas, primarily localised in the urinary bladder are, however, extremely rare. The most frequent ones are low grade non Hodgkin lymphomas, although 3 cases of Hodgkin disease and a few cases of primary extramedullary plasmacytoma of the bladder have been reported, too.(ABSTRACT TRUNCATED AT 400 WORDS)