Fluid-fluid levels in a simple bone cyst on magnetic resonance imaging.

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.