Primary leiomyoma of the inferior vena cava mimicking a cystic neoplasm of the pancreas: a case report.

Benign smooth muscle tumors of the inferior vena cava (IVC) are unusual, but mostly consist of intravenous leiomyomatosis, which arises from the uterus. Primary leiomyoma of the IVC is extremely rare. Here, we report a primary leiomyoma of the IVC, misleadingly reported as a cystic neoplasm of the pancreas in images. Immunohistochemical analysis was positive for (estrogen receptor) ER and (progesterone receptor) PR, indicating gynecologic leiomyomas. The use of ER and PR immunostaining is recommended to help distinguish between somatic and gynecologic leiomyomas, whose criteria of malignancy differ.