A 55-year-old Japanese woman presented with right knee
pain of 1-month duration. Radiological studies revealed bilateral mild osteoarthritic changes in the medial knee joint compartment and symmetrical
cysts in the upper tibial metaphyses, extending to the epiphyses.
Intraosseous ganglion was considered the most probable diagnosis. However, intraoperatively, serous fluid-filled cavities were recognized; these were curetted and filled with
hydroxyapatite granules. Histopathological examination of the
cyst wall revealed thin fibrous tissue formed of
collagen fibers without a lining cell layer, with scattered lymphocytes, histiocytes, irregular masses of
fibrin-like material, and periosteal osteocartilagenous callus formation; a picture compatible with simple
bone cysts. Bilateral symmetrical
cysts of the upper tibial metaphyses extending to the epiphyses are extremely rare. A literature review revealed that the age incidence, and bony locations of multiple and epiphyseal simple
bone cysts are atypical in relation to the classic metaphyseal simple
bone cysts. Also, multiple and epiphyseal simple
bone cysts have a better prognosis than the classic metaphyseal ones. Four clinicoanatomic varieties of simple
bone cysts are recognized; classic metaphyseal, nontubular, epiphyseal, and multiple.