Primary Renal Leiomyoma

Renal leiomyoma is a rare smooth muscle tumor accounting for 0.3% of all nephrectomies and 1.5% of all benign neoplasms.[1] They predominantly affect the female population between the second and fifth decades of life. Renal leiomyoma is predominantly asymptomatic and discovered incidentally on autopsy or when the patient is screened for some other symptoms. The most common presentations are abdominal mass, flank pain, and/or microscopic haematuria.[2] In the kidney, the lower pole is commonly involved. Leiomyomas are mostly subcapsular (53%) or capsular (37%), and these occur less often in the renal pelvis (10%) as these sites normally contain smooth muscles.[2] Macroscopically, these tumors are well circumscribed. The cut surfaces appear tan to white with a whorling pattern. Cystic degeneration is common.[3] Microscopically, long interlacing fascicles of spindle cells are seen. The presence of necrosis, atypia, or mitosis warrants the diagnosis of leiomyosarcoma and is hence looked for. Clinically, the important differential diagnosis includes renal cell carcinoma (RCC) and oncocytoma. Microscopically, stromal predominant angiomyolipoma (AML) also needs exclusion through thorough tissue sampling. Immunohistochemically, the diagnosis of leiomyoma is supported by diffuse smooth muscle actin (SMA) positivity and negativity for melanocytic markers (HMB45 and/or Melan-A). Both AML and oncocytoma are benign and require nephron-sparing surgery (NSS) like leiomyoma. However, RCCs are the most common outcome of contrast-enhancing renal mass and need elaborate management.[4] In the case of renal leiomyoma, the choice between partial and radical nephrectomy depends upon the tumor size and its location. There is no documentation of metastasis to date in the literature and most of the patients remain alive.[5]