Open quiz solution: Case report 728

: A 69-year-old woman with a 25-year history of recurrent sciatica presented with an expanding lytic lesion of the right side of the first sacral vertebra. Histological examination proved the lesion to be a DF. DF is usually diagnosed in young patients and is very rarely located in the spine and sacrum. The growth rate of the tumor was presumed to be very low because it had not progressed from radiological studies performed 9 years previously. The clinical, radiological, and pathological features of DF are described, and the differential diagnoses are discussed. The most difficult problem is to distinguish DF from a low-grade fibrosarcoma or chordoma.