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Q1: Describe the radiological features in figures 1 and 2
The plain radiograph (fig 1) shows an extensive lytic lesion in the middle third of the tibial diaphysis with a reactive bone at the periphery and breach in cortex laterally. There is expansion of the tibia with remodelling and bowing deformity with areas of ossification in the central lytic area. The tibial cortex appears discontinuous anteriorly and posteriorly on the lateral view. The fibula is also affected. The presence of soft tissue swelling can also be noted on these plain films. In addition, there is a second lesion distally in the tibial metaphysis.
The MRI scan (fig 2) shows low signal intensity in the medullary canal. The cortex is breached. There is extension into the surrounding soft tissues with associated oedema. The marrow signal in the fibula appears normal.
Q2: What is the differential diagnosis?1
Monostotic fibrous dysplasia
Q3: What is the management of this condition?
A biopsy is indicated to confirm diagnosis. In this case an open biopsy was performed that showed the histological pattern seen in figure 3. The biopsy specimen was taken from the junctional zone of the lytic lesion. Macroscopically there were four white fragments, the largest fragment measures 0.4×0.3×0.2 cm. Microscopically, trabeculae of lamellar and woven bone were present. The bony trabeculae were rimmed by numerous osteoblasts and the intervening spaces showed cellular, spindle shaped connective tissue with a vague whorled architecture. Occasional osteoclast-like multinucleated cells were seen. There was no evidence of malignancy. Microbiological cultures were negative.
After the biopsy, the leg was immobilised in an above knee cast for six weeks. The foot deformity being correctable was maintained in the cast. In view of the benign nature of the lesion and its tendency to run a regressive course the tibia was splinted and an ankle foot orthosis given at six weeks. On regular follow up over a few years the lesion was healing up with internal torsion of the tibia. At the most recent follow up, the internal tibial torsion was 15 degrees with procurvatum but the patient was asymptomatic. His radiographs (figs 4 and 5) showed regression of the lesion. He remains under regular follow up for clinical and radiological assessment.
Osteofibrous dysplasia was first reported by Frangenheim in 1921. Campanacci described the lesion in 1976. Several theories have been proposed for the aetiology of osteofibrous dysplasia: (1) excessive bone resorption with fibrous repair of the defect; (2) variant of fibrous dysplasia; (3) abnormal periosteal blood circulation.1 The lesion is slightly more common in boys usually appearing in the first decade of life. Long bones are commonly involved with the diaphysis mainly affected, for example, tibia. Clinically, the common presentation is a fusiform diaphyseal swelling, which is usually painless. There may be associated bowing. On pathological examination, the periosteum is intact with a thinning of the involved cortex. Histologically, the tissue is similar to fibrous dysplasia with spicules of trabecular bone and fibrous stroma. The presence of osteoblasts around the spicules is a distinguishing feature from fibrous dysplasia.2 Recent immunohistochemical studies have shown isolated cytokeratin positive cells in the stroma of osteofibrous dysplasia. Radiological features include a lytic lesion in the diaphysis with cortical expansion. The epiphysis is spared. Monoostotic fibrous dysplasia and adamantinoma are important differentials of osteofibrous dysplasia.3 Fibrous dysplasia is commonly seen in the second decade with ground glass radiological appearance and histologically the bony trabeculae in the fibrous stroma are rarely ringed with osteoblasts. Adamantinomas occur in patients over 10 years of age. Radiographs show aggressive moth eaten destruction and histologically, this possible relation is based on the finding that rare cytokeratin positive cells are found in osteofibrous dysplasia. When present in greater numbers, cords of these cytokeratin positive cells set in a fibrous background are diagnostic of adamantinoma. The natural history of osteofibrous dysplasia varies. The commonest sequela is initial slow growth with regression at maturity. As, curettage of the lesion in a young child is often followed by recurrence, a conservative approach is recommended. Cast immobilisation of a pathological fracture and bracing for progressive angular deformity is indicated. A non-operative approach is also recommended in the adolescent. However, if enlargement of the lesion occurs, marginal excision may be a useful option.
Osteofibrous dysplasia of the tibia.