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Benign metastasizing leiomyoma (BML) is a rare disease of women, which is characterized by noninvasive, well-circumscribed tumors composed of differentiated smooth muscle cells, localized to sites other than the uterus.15 Lungs and lymph nodes6 are the most common sites involved, but BMLs have also been identified in the mediastinum,7,8 retroperitoneum,9 vascular channels,10 bone,11 heart,12 skeletal muscle,13 and soft tissues.14 Pulmonary BML has been associated primarily with uterine leiomyomas and has been mainly diagnosed in patients who have undergone uterine myomectomy or hysterectomy.1,4

The first report of BML, in 1939, described a 36-year-old woman who presented with dyspnea and wheezing. Chest X-rays showed multiple lung nodules. At autopsy, lymph nodes, uterus, and lungs showed nodules of smooth muscle cells with identical morphology15 and the term “metastasizing fibroleiomyoma of the uterus” was adopted. This term was later abandoned and the name BML was proposed because of the metastatic behavior of this disease.

Pathologically, BML lung nodules resemble hamartomas (the most common benign lung tumor), low-grade leiomyosarcomas, and nodules of proliferating smooth muscle cells.16 Pulmonary BML is usually asymptomatic and presents with either single or multiple lung nodules of varying sizes.17 The tumors do not appear to invade adjacent tissues.18 BML, however, represents a diagnostic and therapeutic challenge because of its pathogenesis and metastatic potential.


The occurrence and prevalence of pulmonary BML is unknown. There are over 100 cases of BML reported in the literature but only a few studies reported more than one case. BML is a rare disease, found primarily in premenopausal women who have undergone surgical procedures for treatment of uterine leiomyomas.1,4,18 However, cases of lung BML have also been reported in women with no history of these surgical procedures.19 Leiomyomas, including BML of the lung, may be found in women and, to a lesser extent, in men and children.20 There is no ethnic or racial preference for BML and this differs from uterine leiomyoma, which is more frequent in African-American women.21 Cases of BML have been reported from countries all over the world4,22 including, but not limited to, the United States,19 Portugal,23 Brazil,24 China,25 India,14 South Korea,13 Japan,26 and Turkey.6

Clinical Presentation

Most cases of lung BML have been identified as an incidental finding on imaging procedures performed for other purposes (Fig. 63-1).1 BML nodules may present in premenopausal women as unilateral or bilateral tumors with no specific lobar distribution.17,27 A number of different types of uterine tumors (e.g., leiomyoma, smooth muscle tumors of uncertain malignant potential, leiomyosarcomas, other smooth muscle tumors, endometrial stromal tumors) are associated with the diagnosis of BML. ...

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