BERKELEY, CA (UroToday.com) - Renal leiomyomas are rare and benign tumors which originate from smooth muscle cells of the renal capsule, pelvis, calices, and blood vessels.
Renal leiomyomas are divided into two groups on the basis of the clinical features: a) small tumors, asymptomatic, sometimes multifocal, incidentally detected in autopsy or after radical nephrectomy; and b) big tumors, often singular lesions, clinically manifested by symptoms/signs such as pain or a palpable abdominal mass. 
These lesions do not exhibit aggressive behavior and they don’t develop metastasis, however, surgery cannot be avoided because imaging alone cannot be utilized in making a definitive diagnosis. The distinction between leiomyomas and other malignant lesions as all renal cell carcinoma or leiomyosarcoma is still possible only by histological examination.
Ultrasonographic evaluation detects leiomyoma as a hypoechoic lesion that could appear solid or cystic. In the literature, some authors described CT scan features helpful for differential diagnosis: a) density: all leiomyomas examined before contrast were hyperdense compared to the kidney, with density similar to muscles, and after contrast medium injection, all the lesions had a lower enhancement than surrounding renal parenchyma; and b) localization and margins: these lesions usually have a peripheral location with well-defined margins and above all, no signs of infiltration into surrounding tissues. 
These radiological features allow us to suspect leiomyoma in differential diagnosis but they don't make it possible to rule out malignant diseases. For this reason the gold standard treatment is surgery.
Renal leiomyiomas can be treated with radical nephrectomy in suspicious cases or with conservative surgery in case of small lesions. In asymptomatic small masses, biopsy could possibly avoid the surgery but this remains a controversial topic.
- Steiner MS, Quinlan D, Goldman SM, et al.: Leiomyoma of the kidney: presentation of 4 new cases and the role of computerized tomography. J Urol 1990 143: 994-998
- Derchi LE, et al.: Imaging of renal leiomyomas. Acta Radiol. 2008 Sep; 49(7):833-8
Eugenio Brunocilla, MD, PhD, Cristian Vincenzo Pultrone, MD, Riccardo Schiavina, MD, PhD, Valerio Vagnoni, MD, and Giuseppe Martorana, MD, PhD as part of Beyond the Abstracton UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
Department of Urology
University of Bologna
S. Orsola-Malpighi Hospital