Solitary benign metastasizing leiomyoma: imaging features and pathological findings

A 51-year-old woman presented with dyspnea on exertion, dry cough, dyslipidemia, type 2 diabetes, and liver steatosis. Twenty years prior, she had undergone hysterectomy and unilateral oophorectomy because of uterine leiomyomas. A chest X-ray showed a solitary pulmonary nodule in the right upper lobe. The nodule was oval in shape, being approximately 24 mm × 30 mm. A CT scan of the chest confirmed that the lesion was a solitary, well circumscribed-nodule that had regular borders and was located in the posterior segment of the right upper lobe. As can be seen in Figures 1A and 1B, there was delayed contrast enhancement (50 HU before contrast injection, 55 HU within 25 s after contrast injection, and 100 HU within 5 min after contrast injection). Contrast-enhanced magnetic resonance imaging was performed, and the nodule showed slightly high signal intensity on T1-weighted images and homogeneous enhancement (Figures 1C and 1D). The lesion showed signal intensity similar to that of muscle on T2-weighted images. In-phase and out-of-phase imaging, fat-saturated imaging, and diffusion-weighted imaging provided no additional findings. A chest X-ray performed three years earlier had shown no lesions. Because the imaging findings were inconclusive and because of the risk of malignancy, the patient underwent video-assisted thoracoscopic surgery for nodule resection. Pathological examination revealed a nodular proliferation composed of smooth muscle cells without atypia and areas of hyalinization, a finding that was consistent with leiomyoma (Figure 2A). Immunohistochemical analysis of the lesion showed that estrogen receptors and progesterone receptors were positive, and a diagnosis of benign metastasizing leiomyoma (BML) was made despite the atypical presentation, i.e., a solitary pulmonary nodule (Figures 2B and 2C). BML is a rare neoplastic process in which leiomyomas of the uterus metastasize to distant sites, the most common of which are the lungs. BML is usually asymptomatic, and the diagnosis is based on incidental imaging findings of multiple pulmonary nodules or, more rarely, a single nodule. The term metastasizing fibroleiomyoma of the uterus was introduced by Steiner in 1939 to described multiple nodules of proliferating smooth muscle cells in the lung of women with a history of hysterectomy. Different mechanisms of spread of uterine leiomyomas have been proposed. It has been suggested that smooth muscle cells spread to the lungs after uterine extension into pelvic venous channels; that tumors gain venous access from surgical trauma during hysterectomy; and that the lesions represent metastatic foci arising from low-grade leiomyosarcomas. In …