[A rare diaphyseal bone tumor: degenerative mucoid cyst].

The purpose of the study was to clarify the clinico pathological features of periosteal ganglion. The authors present a case of an unusual diaphyseal bony tumor in a 27 years old man. The diagnosis of diaphyseal periosteal ganglion cyst was made on roentgenographic appearance, presence of mucoid material and histologic evidence of a synovial type cellular lining. The patient was successfully treated with excision. The follow-up examination showed no recurrence one year after surgery. The radiological differential diagnosis were considered and possible pathogenes for a periosteal ganglion was discussed. Periosteal ganglia must be considered as a cause of cortical erosions. This lesion may radiologically mimic other periosteal lesions. Treatment with excision is successful in most cases.