Axial T2-weighted fast recovery fast spin-echo (FRFSE) MRI of the pelvis. Axial T2-weighted fast recovery fast spin-echo (FRFSE) MRI of the pelvis demonstrating an ill-defined lesion representing Ewing's sarcoma within the sacrum (red arrows). The lesion is eccentric to the right involving a large portion of the right sacral ala interspersed with fat, which is compatible with areas of bone infarction. The site of the open surgical biopsy within the right posterior lumbar paraspinal and subcutaneous tissues (blue arrows) is also the site of the posterior sacroiliac joint ligament.