Leiomyosarcoma of the Renal Vein That Enlarged Laterally While Preserving the Structure of the Renal Vein Lumen

ABSTRACT Introduction Primary renal vein leiomyosarcoma is an extremely rare disease and the tumor often infiltrates the vessel wall. We report a case of primary renal vein leiomyosarcoma that enlarged while preserving the structure of the renal vein lumen. Case Presentation A 64‐year‐old woman underwent a computed tomography scan, which revealed a left renal hilar mass. Extra‐gastrointestinal stromal tumor, leiomyosarcoma, and inflammatory myofibroblastic tumor remained in the differential diagnoses based on blood, urine, and imaging test findings. The tumor, left renal vein, kidney, and adrenal gland were resected. Hematoxylin–eosin staining revealed a tumor arising from the renal vein wall and proliferating outward beyond the vessel. The diagnosis was primary renal vein leiomyosarcoma. Conclusion When a well‐defined solid tumor adjacent to the renal vein is identified, leiomyosarcoma should be considered in the differential diagnosis, and complete resection of the tumor should be pursued.