Conventional renal cell carcinoma with renal capsular leiomyoma: a diagnostic dilemma

Primary renal leiomyomas are very rare benign tumors of the kidney, arising from smooth muscle cells of the renal capsule, pelvis or blood vessels. Simultaneous occurrence of a leiomyoma with conventional renal cell carcinoma (RCC) in the same kidney is an extremely rare incidence. Herein we describe a case, which to the best of our knowledge is the second reported case in the English literature. This 70-year-old female presented in surgical out-patient department with the complaints of hematuria and abdominal pain. Subsequently, on computed tomography a multifocal mass was noted in the right kidney, measuring 4.5 cm Χ 3 cm Χ 2 cm and 1 cm Χ 0.5 cm Χ 0.5 cm respectively. A radical nephrectomy was performed with the clinical diagnosis of a multifocal RCC. Histopathological examination revealed a conventional RCC in the larger nodule, whereas the smaller nodule showed a sub capsular leiomyoma, which was immune-positive for smooth muscle actin and HMB45. In the index case, radiology could not differentiate between the RCC and leiomyoma. Apart from being a radiological diagnostic dilemma, rare HMB45 immunostain positivity in capsular leiomyoma may create diagnostic dilemma for histopathologists too. Sole HMB45 positivity should not distract one to diagnose this lesion as an angiomyolipoma, unless the other components are seen.