A 58-Year-Old Woman's Odyssey With Bilateral Nodular Opacities Comes to a Diagnosis.

Benign metastasizing leiomyoma (BML) is an uncommon entity in which histologically benign smooth muscle tumors appear at distant sites, most frequently the lungs, in women with a history of uterine leiomyoma treated surgically. Despite its benign pathology, BML often presents radiologically in a pattern that mimics metastatic malignancy, resulting in substantial diagnostic uncertainty. Awareness of this condition is essential for avoiding unnecessary or overly aggressive interventions. We describe the case of a 58-year-old woman and active smoker with a significant 40-pack-year history who was referred following the incidental discovery of multiple bilateral pulmonary nodules and two enlarging masses during routine coronary CT angiography. Remarkably, retrospective review revealed a 23-year history of slowly progressive pulmonary nodules. The patient was asymptomatic except for a chronic intermittent productive cough. Laboratory testing, including immunologic profiling and tumor markers, was unremarkable, apart from elevated CA-125 levels. Bronchoscopy and transbronchial needle aspiration demonstrated nonspecific fibrosis without evidence of malignancy or infection. Fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging showed multiple photopenic nodules and two non-FDG-avid masses, further complicating the differential diagnosis, which initially included metastatic cancer, granulomatous disease, and primary pulmonary neoplasms. Given the increasing size of the dominant left upper lobe lesion and persistent diagnostic ambiguity, the patient underwent video-assisted thoracoscopic surgery with left upper lobectomy. Histopathological examination revealed intersecting bundles of bland smooth muscle cells without atypia or necrosis, while immunohistochemistry demonstrated strong positivity for SMA, desmin, caldesmon, and estrogen receptors, consistent with pulmonary benign metastasizing leiomyoma. These findings were correlated with the patient's remote history of hysterectomy for uterine leiomyoma. This case highlights the diagnostic challenges of BML, particularly when radiologic findings resemble metastatic malignancy over many years. Recognition of its characteristic clinical, imaging, and histologic features is essential to avoid misdiagnosis and overtreatment. Management should be individualized and may include surgical resection, hormonal therapy, or careful surveillance. Long-term follow-up is recommended due to the condition's variable clinical course and potential for progression.