[Leiomyoma of the kidney. Differential diagnostic aspects of renal cell carcinoma with increasing clinical relevance].

Renal leiomyoma is a rare benign tumor which has its origin in smooth muscle cells of different structures of the kidney. The clinical incidence of renal leiomyoma is much lower than the frequency described in large autopsy studies. Renal leiomyomas are mainly located in the renal capsula and pelvis or next to those structures. Clinical symptoms are nonspecific (e.g., flank pain or flank tumor) or completely absent, making most of the leiomyomas an incidental finding during routine diagnostics. A differential diagnosis between renal leiomyoma and renal cell carcinoma on the basis of medical imaging is extremely difficult. Therefore, laparotomy and nephrectomy are performed in most cases of suspected renal cell carcinoma. The definitive diagnosis of a leiomyoma is only possible after histological examination of the tumor. Due to the rising number of diagnoses resulting from improved medical imaging, renal leiomyomas are gaining more importance in the differential diagnosis of renal cell carcinoma, especially with respect to kidney-sparing surgery.