Benign mesenchymoma of the round ligament. A report of two cases with immunohistochemistry.

Benign mesenchymomas are tumors composed of an admixture of two or more mature mesenchymal tissue types. Clinically and histologically they are benign lesions. However, they are seldom encapsulated and therefore may recur locally if incompletely excised. The authors report on two benign mesenchymomas composed of mature fat, thin-walled small and medium size vessels, and spindle cells demonstrated to be smooth muscle by immunohistochemical studies. They were diagnosed in women in their 50s. Both were located in the round ligament of the uterus. One was discovered incidentally during hysterectomy, and the other was unusually large, being diagnosed preoperatively as a retroperitoneal liposarcoma. Most round ligament tumors are leiomyomas or fibromas. To the authors' knowledge, this is the first report of benign mesenchymomas occurring in this location.