A case of intravenous leiomyomatosis with high levels of hyaluronan.

Intravenous leiomyomatosis (IVL) is a rare benign tumor. The clinical behavior can be life-threatening due to extension through the pelvic veins. A 70-year-old woman was referred to our hospital with IVL originating from a uterine leiomyoma and extending to the inferior vena cava. The patient was diagnosed on the basis of the results of various studies, and the tumor was resected completely through a single-stage approach. The intravascular tumor was 20 cm long, multinodular and rubbery. Microscopic findings showed benign smooth muscle that was partly hyalinized and fibrous. Immunohistochemical studies revealed that hyaluronan was expressed more prominently in IVL than in uterine leiomyomas. IVL has viscoelastic properties and contains a large amount of hyaluronan, which may promote invasion during pathogenesis.