Renal Leiomyoma in a Female Adult: A Histopathological Case Report.

Renal leiomyomas are rare benign mesenchymal tumors that arise from the smooth muscle cells in the renal capsule, renal pelvis, and the smooth muscles of vessels in the kidney. They are usually found by accident during autopsies or on different imaging modalities made on other occasions. The clinical presentation may include hematuria and abdominal or flank pain, although renal leiomyomas are most frequently asymptomatic. This case concerns a 45-year-old woman with an asymptomatic tumor mass in the left kidney, discovered incidentally on an outpatient CT scan conducted on an unrelated occasion. Histological examination revealed well-demarcated tumor formation on regular hematoxylin and eosin (H&E) staining consisting of intersecting fascicles of spindle cells with blunt-ended, cigar-shaped nuclei and eosinophilic cytoplasm. The neoplasm showed no mitotic activity. Immunohistochemistry (IHC) was performed to exclude different spindle cell pathologies, such as solitary fibrous tumor of the kidney, primary leiomyosarcoma, and, less probably, sarcomatoid variants of renal cell carcinoma (RCC). Tumor cell cytoplasm was positive for h-caldesmon, smooth muscle actin (SMA), and desmin. The proliferation index Kiel-67 (Ki-67) was evaluated as less than 1%. Considering the microscopic description and the IHC results, the neoplasm was interpreted as a renal leiomyoma. In light of the rarity of these tumors, pathologists should consider differential diagnosis with precision. In challenging cases, immunohistochemical examination can be beneficial to distinguish between several spindle cell renal neoplasms, such as solitary fibrous tumor, leiomyosarcoma, sarcomatoid variant of RCC, fat-poor angiomyolipoma, benign peripheral nerve sheath tumors, renomedullary interstitial cell tumor, benign fibrous histiocytoma, primary angiosarcoma, mucinous tubular and spindle cell renal cell carcinoma (MTSRCC).