[A Case of Venous Leiomyosarcoma of the Inferior Vena Cava Diagnosed Preoperatively as an Adrenal Tumor].

A 72-year-old woman was referred to our hospital complaining of abdominal pain. Contrast enhanced computed tomography revealed a 53 mm solid tumor with low contrast enhancement on the medial aspect of the right adrenal gland. On magnetic resonance imaging, the tumor showed low signal intensity on T1-weighted images, high signal intensity on T2-weighted images, and high signal intensity on diffusion-weighted images. The patient was diagnosed as having a right adrenal tumor and was referred to our hospital for surgery. Laparoscopic right adrenalectomy was performed. During surgery, we could easily peel the tumor from the adrenal gland, but it was strongly adhered at the inferior vena cava. Considering the possibility of a primary tumor of the inferior vena cava, we converted to open surgery and achieved complete tumor resection by combined partial resection of the inferior vena cava. The cut surface of the tumor was white and firm. Histopathological examination with hematoxylin-eosin staining revealed spindle cell proliferation forming bundle-like structures. Immunohistochemical staining was positive for DESMIN and α-SMA, suggesting leiomyosarcoma. Furthermore, the vascular smooth muscle structure of the resected inferior vena cava was completely replaced by leiomyosarcoma. Therefore, our diagnosis was venous leiomyosarcoma originating from the inferior vena cava. The patient has remained recurrence-free at 21 months after surgery.