Marrow edema cannot be reliably distinguished from osteomyelitis with MR imaging. Gadopentetate dimeglumine is of limited use. Some previously published false-positive reports of osteomyelitis were most likely due to edema of the marrow. MR imaging is useful in planning surgery of the infected diabetic foot, as it enables reliable distinction between normal and abnormal areas.

An unusual case is presented here of simple bone cyst (SBC) with fluid-fluid levels on MR and cementum-like substance on microscopy in an atypical location in the distal femur. Fluid-fluid levels are commonly described in the literature within aneurysmal bone cysts, giant cell tumour, chondroblastomas and telangiectatic osteosarcomas, but a literature review revealed only one reported case with multiple fluid levels occurring in a simple bone cyst on MRI. A cementum-like matrix is diagnostic of SBC and is seen in approximately 10% of cases.