A 49-year-old woman with an untreated uterine leiomyoma was found to have a solitary nodule in the left upper lobe on chest computed tomography (CT) seven years ago. We adopted a wait-and-see approach, and the nodule did not increase in size. She was referred to our hospital because of epigastralgia, and chest CT showed multiple nodules in bilateral lung fields that had exacerbated since the initial examination. We performed a left upper lobe resection in order to make a definitive diagnosis. The resected tumor revealed pathological proliferation of spindle cells without any nuclear atypia or mitotic figures. Immunohistochemical staining demonstrated positive reaction for α-smooth muscle actin, progesterone and estrogen receptors. Therefore, we diagnosed the tumor as a pulmonary benign metastasizing leiomyoma.
Benign metastasizing leiomyoma is a rare disease that represents the extrauterine spread of a benign uterine leiomyoma. In most cases, there is a previous history of hysterectomy for uterine leiomyoma. This case was, however, diagnosed as benign metastasizing leiomyoma before treatment of uterine leiomyoma. Benign metastasizing leiomyoma may be considered in the differential diagnosis when a lung nodule is detected in a patient with an untreated uterine leiomyoma.