A chondroblastoma is a rare benign cartilaginous neoplasm that characteristically arises in the epiphysis or apophysis of a long bone in young patients 1-2,7. It is however one of most frequent benign epiphyseal neoplasm in skeletally immature patients.
Chondroblastomas represent less than 1% of all primary bone tumours, occurring predominantly in young patients (< 20 years of age) 7. There is a male predilection 7.
Clinical presentation is non-specific and may include joint pain, muscle wasting, tenderness, and swelling / local mass.
Microscopically they are composed of chondroblasts (no surprise there), chondroid matrix, cartilage with occasional giant multi-nucleated cells (which may lead to the incorrect diagnosis of giant cell tumour). Surrounding the chondroblasts, which are typically polyhedral cells, is thin calcification which resembles chicken-wire 7,10.
Malignant transformation has been seen in a small proportion of cases, with local and vascular invasion, and distant metastases.
Aneurysmal bone cysts can be seen secondarily to underlying chondroblastoma.
Chondroblastomas most frequently arise in the epiphyses of long bones, with 70% occurring in the humerus (most frequent), femur and tibia 9. ~ 10% are found in the hands and feet 7.
Chondroblastomas are seen as well defined lytic lesions, with either smooth or lobulated margins with a thin sclerotic rim, arising in the epiphysis or apophysis of long tubular bone such as the femur, humerus, or tibia. Internal calcifications can be seen in up to 40-60% of cases 7,9. A joint effusion is seen in ~1/3 of patients.
They range in size from 1-10cm, with most being 3-4cm at diagnosis 10.
CT demonstrates the plain film findings with better delineation of the relationship to the growth plate and articular surface. Solid periosteal reaction (seen in up to 50% of cases) and internal calcification (calcified matrix seen in ~ 1/2 of cases) and cortical breach are also more easily appreciated 7-8. Endosteal scalloping may be seen 10.
MRI is ideal for the evaluation of transphyseal or transcortical extension, and for demonstrating associated surrounding bone marrow oedema, which is seen in a large proportion of cases 5,7.
These lesions have signal typical of cartilage:
- T1 - lesion itself is of low to intermediate signal
- T2 / STIR - lesion is of intermediate to high signal
Fluid-fluid levels may occasionally be seen (see fluid fluid level containing bone lesions) presumably due to an associated aneurysmal bone cyst 4
Treatment and prognosis
Treatment typically consists of curettage and packing of the resulting cavity with either bone or bone cement (polymethylmethacrylate). Radiofrequency ablation has also been used 7.
Unfortunately due to their proximity to the articlular surface and growth plate complete eradication is difficult. As a result recurrence rates are relatively high (8 - 20%), and injury to the growth plate may result in growth arrest and limb-length discrepancy 7.
Complications associated with chondroblastomas include pathologic fractures and rarely, malignant transformation and pulmonary metastasis 6.
The differential is that of other lesions which have a predilection for the epiphysis or apophysis (see differential for an epiphyseal lesion). Specific lesions to be considered include 10:
- clear cell chondrosarcoma - see chondroblastoma vs clear cell chondrosarcoma
- osteomyelitis with abscess (e.g. Brodie abscess)
- intraosseous ganglion
- giant cell tumour - older age group (closed physis)
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