Answer: Intravenous leiomyomatosis

Histology: Gross examination discloses an enlarged uterus with solitary or multiple masses; wormlike plugs of tumor are seen within myometrial veins.

Histologic examination reveals proliferations of benign-appearing smooth muscle within myometrial vessels, at least some of which are large veins. Several variants have been described, including cellular, epithelioid, IVL with bizarre nuclei, lipoleiomyomatous, and myxoid (similar to the histologic variants of leiomyoma). Immunhistochemically, the tumors are positive for vimentin, desmin, alpha-smooth muscle actin, and estrogen and progesterone receptors.

Discussion: Intravenous leiomyomatosis (IVL) is a rare smooth muscle proliferation of special interest because of its quasi-malignant behavior. It arises from the uterus with vermiform extensions in some cases into the inferior vena cava, which may ultimately extend into the right heart. The neoplastic smooth muscle of intravenous leiomyomatosis resembles that of benign uterine leiomyomata, and may include the same histological variants found in the uterus. The neoplastic smooth muscle cells of IVL express estrogen and progesterone receptors and tumor growth appears to respond to hormonal manipulation.

In a large series, the patient ages ranged from 28 to 76 years (median, 42 years). Clinically, symptoms are similar to the presentation of uterine leiomyomas (abnormal uterine bleeding, pelvic pain). On pelvic examination, an enlarged uterus is a common finding. Intraoperatively, extension of tumor into the broad ligament vessels is occasionally described, and may also be seen on gross examination of the specimen.

The clinical course is generally benign, but recurrences and pulmonary extension/metastasis have been reported.

IVL should be distinguished from other uterine tumors, particularly endometrial stromal sarcoma and leiomyosarcoma, which differ in their behavior and management.