[Unclassified renal cell carcinoma accompanying pyonephrosis: a case report].

A 73-year-old male, admitted to a local hospital because of fever and consciousness disturbance, was referred to our institute. He had a history of long-term steroid administration and diabetes mellitus. Under diagnosis of severe right pyonephrosis associated with severe inflammatory response syndrome as well as disseminated intravascular coagulopathy, he was transferred to our hospital. Computed tomography and magnetic resonance imaging showed a mass 5 cm in diameter at the right ureteropelvic junction and lymph node swelling at the renal hilum, suggesting obstructive pyonephrosis by a malignant tumor such as renal pelvic cancer. Since the patient failed to respond to conservative medical treatment including polymyxin B hemoperfusion, hemodialysis, and antimicrobials, we performed right nephrectomy. Histopathological examination demonstrated that the tumor obstructing the pelvis arose from the parenchyme under the muscle layer, and was diagnosed as unclassified renal cell carcinoma while the renal pelvic epithelium was normal. Although his general condition and laboratory data transiently improved after nephrectomy, he died of carcinomatous peritonitis 30 days postoperatively. We advocate that, in the case of pyonephrosis with a lesion highly suspected to be an infiltrating neoplasm, nephrectomy is justified as first choice to control the septic condition.