PET/CT of Delayed Uterine Leiomyoma Metastasizing to Lung and Femur

DISCUSSION

Benign metastasizing leiomyoma (BML) is a rare disease characterized by histologically benign extrauterine smooth cell metastatic tumors in patients with prior history of uterine leiomyomas. BML may occur years after hysterectomy for benign uterine leiomyomas; however, few cases have been reported in women without previous uterine surgery (1). The lung is the site most affected, with rare involvement of the brain, heart, spine, retroperitoneum, and bone (1–3). Although several theories detail the route of metastasis, the etiology and pathogenesis of BML still remain unclear. A few theories suggest a metaplastic process or hematologic spread of uterine leiomyomatous tissue at the time of hysterectomy (1). Even though MR and CT depicted well the femoral and chest tumors in our patient, ¹⁸F-FDG PET/CT provided the metabolic characteristics of these lesions, the whole-body assessment for potential additional lesions/metastasis, and the postsurgical surveillance of BML. Leiomyosarcomas are ¹⁸F-FDG–avid, whereas BML typically lacks tracer uptake. However, a small proportion of BML may exhibit mild borderline tracer uptake as seen in our case (2). ¹⁸F-FES (16α-¹⁸F-fluoro-17β-estradiol) PET/CT may provide useful information about BML estrogen receptor expression with an option for antihormonal therapy (4). Histologically, the absence of cellular atypia and low mitotic activity favor a diagnosis of BML. However, low-grade and slow-growing leiomyosarcoma cannot be totally excluded from the differential diagnosis even with benign histologic features.