Benign metastasizing leiomyoma: a rare case of osseous involvement.

Benign metastasizing leiomyoma is a rare entity characterized by the metastasis of histologically benign smooth muscle tumors that originate from uterine leiomyomas. Patients are typically women with a history of uterine leiomyomas for which they have undergone operative treatment. Benign metastasizing leiomyoma most frequently involves the lungs but has been described in other locations. Osseous involvement is rare, with less than 20 cases reported in literature, the majority occurring in the spine. The current case is that of a 67-year-old female with a history of breast carcinoma with multiple lytic osseous lesions involving the pelvis and scapula, initially suspected to represent metastatic disease. Following multi-modality imaging workup including radiographs, CT, MRI, and PET/CT, biopsy revealed benign metastasizing leiomyoma. This case illustrates the multimodality imaging appearance of this rare entity. Radiographs and CT typically show well-defined lytic lesion(s) without aggressive periosteal reaction. On MRI, lesions are often T1 and T2 hypointense, with diffuse enhancement following the administration of contrast. Lesions typically display no or mild FDG uptake on PET/CT, however, varying levels of FDG uptake have been reported in literature. Benign metastasizing leiomyoma with osseous involvement is a rare but clinically significant entity that requires a high index of suspicion in women with a history of uterine leiomyomas and new bone lesions. Radiologists should be aware of this entity so that they may include benign metastasizing leiomyoma in the differential diagnosis when appropriate.