Solitary fibrous tumour of the renal peripelvis.

Solitary fibrous tumours (SFTs) are rare spindle cell neoplasms generally associated with the serosal surface, especially the pleura. This report describes two SFTs arising in the renal peripelvis, occurring in 33- and 36-year-old females. The lesions lacked the characteristic features of other recognized neoplasms that occur in the kidney. Immunohistochemically, the tumour cells were diffusely and strongly positive for vimentin and CD34, and some tumour cells expressed alpha-smooth muscle actin. Both tumours were diploid by flow cytometry. Both patients have had benign clinical courses with 7.5- and 1-year follow-up. The findings suggest that the SFTs may originate from peripelvic mesenchymal cells, a new location for SFT. SFT should be included in the differential diagnosis of spindle cell tumours arising in the renal pelvis and peripelvis.