The authors present a case of a 42-year-old female who developed a leiomyosarcoma of the right
proximal tibia that appeared radiologically similar to a giant cell tumor. Histology revealed spindle cells
running in whorl-like fashion with focal atypia and low mitotic figures. The immuno-stains revealed positive
reactivity for alpha-smooth muscle (SMA), muscle actin and cytokeratin (AE1/AE3). The authors rendered a
diagnosis of low-grade leiomyosarcoma of bone. The lesion was considered a primary lesion since the patient
did not have other leiomyomatous tumors. The MRI showed hypo- to iso- signal intensity on T1-weighted
imaging and heterogeneous intensity on T2-weighted imaging. This was likely due to admixed fibrotic tissue
in the lesion. The tumor cells were not positive for Ebstein-Barr virus by in-situ hybridization as seen in
leiomyomatous tumors in immunodeficiency patients.

Keywords: Leiomyosarcoma, Bone, MRI, Imaging, Immunostains