Lung metastases from benign uterine leiomyoma: does 18-FDG-PET/CT have a role to play?

Uterine leiomyomas are the most common benign gynaecological tumours. However, 0.13 to 6% of them have malignant potential (Robboy et al. Environ Health Perspect 108(Suppl 5):779-784, 2000). Uterine smooth muscle tumours with unusual growth patterns include a spectrum of lesions such as intravenous leiomyomatosis, benign metastasizing leiomyoma and disseminated peritoneal leiomyomatosis (Vaquero et al. J Minim Invasive Gynecol 16:263-268, 2009). Benign metastasizing leiomyoma (BML) is a very rare condition with around 100 cases reported to date. BML is a cytologically bland, mitotically inactive smooth muscle tumour in extra uterine sites, occurring in conjunction with similarly appearing or previously removed uterine leiomyomas (Beck et al. Hong Kong Med J = Xianggang yi xue za zhi 18:153-155, 2012). Pulmonary metastases are the most common sites of metastases, but other sites include skin, bladder, liver, lymph nodes, oesophagus, skeletal muscles, heart, bones and central nervous system (Jo et al. Korean J Int Med 21:199-201, 2006; Arai et al. Chest 117:921-922, 2000; Kwon et al. Korean J Int Med 21:173-177, 2006; Rivera et al. J Clin Endocrinol Metab 89:3183-3188, 2004; Jautzke et al. Pathol Res Pract 192:215-223, 1996; Goyle et al. Am J Clin Oncol 26:473-476, 2003; Schneider et al. Der Chirurg; Zeitschrift fur alle Gebiete der operativen Medizen 72:308-311, 2001; Andrade et al. Pathol Oncol Res: POR 4:44-47, 1998; Abramson et al. AJR Am J Roentgenol 176:1409-1413, 2001; Yoon et al. Cancer Res Treat 43:131-133, 2011; Egberts et al. Arch Gynecol Obstet 274:319-322, 2006). The condition is more common in late childbearing age, mean age of diagnosis is 43 years (Kwon et al. Korean J Int Med 21:173-177, 2006), suggesting that it is hormone related. Lung metastases in BML are usually an incidental finding during the preoperative assessment; however, on rare occasions, patients are symptomatic with cough, chest pain, haemoptysis or dyspnoea. The differential diagnosis includes pulmonary metastases from leiomyosarcoma, intravenous leiomyomatosis or metastasis from other malignancies. Lung biopsy is the only way to confirm the benign nature of these lesions. Recently, positron emission tomography (PET) scan showed promise in differentiating these benign lesions from malignant lung lesion (Sawai et al. Oncol Lett 14:3641-3646, 2017). We present three cases with pulmonary metastases from BML and discuss the pathogenesis and management of this rare condition.