Case 11
A 16-year-old male presented with a 4 months history of mild discomfort and intermittent swelling about the knee.
A: Presenting AP radiograph. The underexposed radiograph shows a well marginated lesion occupying the medial half of the lateral condyle of the femur. The lesion contains subtle fluffy areas of calcification. The lesion abuts the subch ondral plate and appears to have extended through the cortex into the intercondylar notch. suggesting an aggressive process.
Without further staging the lesion was approached intrarticularly, biopsied, diagnosed by frozen section, and treated by curettage and autogenous bone grafting.
B: A follow-up radiograph at one year. the patient was asymptomatic. Although the reactive rim about the lesion can still be ditinguished, the lesion appears to have ossified. The area about the intercondylar notch is obscured by the overlying patella.
Two years. postoperatively he experienced increasing discomfort and repeated effusions.
C: A lateral radiograph of the knee at that time. The intrarticular area just anterior to the femoral condyle and inferior to the patella contains several discreet areas of calcification.
D: A closer look at that film. These are highly suggerstive of a recurrence of the original process.
An arthrotomy of the knee was done. Several synovial implants were found studding the lining of the knee.
E: A panoramic view of one of the nodules embedded in the synovium. The lower margin of the field contains a rim of reactive bone. The upper portion contains an area of tisssue that is partially calcified.
F: Higher power from the periphery of the previous field. The lower right corner contains a reactive trabeculae surrounded by proliferating fibrovascular reparative tissue. The upper left contains the cellular tissue of the lesion.
G: A low power field from the central portion of the nodule. This field has multiple areas of focal calcification (reddish/brown) embedded in the lesional tissue. Even at this low magnification several small mltinucleated giant cells may be discerned. A small area of more mature chondroid is at the bottom right hand corner.
H: Higher power from the previous field. The left hand portion of the field contains the uncalcified lesional cells. They have the characteristic "paving stone" architecture of chondroblasts and are imbedded in faintly eosinophilic amorphous ground substance. In the right hand portion of the field the ground substance about the cells stains a much deeper reddish/purple indicating calcification and producing the overall pattern of "chicken wire".
I: Higher power of the lesional cells. This magnification brings out the "paving stone" arrangerment of the chondroblasts. The upper left hand corner has a small giant cell.
The presenting radiographs show the usual location of a chondroblastoma. The original curettage was done through a trans-articular approach and the recurrence is almost surely the result of joint contamination during that procedure.
The histologic features of the implanted synovial nodule are typical of chondroblastoma - pavingstone pattern of chondroblasts, islands of immature chondroid, and purplish micro-calcification.
Diagnosis: Recurrent stage 3 chondroblastoma
Despite efforts to control the implants with repeated local excisions, the knee eventually filled with chondroblastomatous tissue and an extra-articular resection of the knee reconstructed by arthrodesis was done.
