Imaging description

In flat bones chondroblastoma is reported to occur in the acetabular region, scapula, ribs, patella, talus, and calcaneus (Figure 92.1).

The epiphyseal location for most chondroblastomas is an important diagnostic imaging feature; the lesion often traverses the epiphyseal plate into the metaphyseal region (Figure 92.2). Radiographically a chondroblastoma reveals a geographic lytic lesion measuring about 2–5 cm in diameter. The majority of chondroblastomas have a thin sclerotic border. Local thinning and expansion of the overlying cortical bone is a common finding. In a study by Brower et al. they observed a periosteal reaction distal to the tumor in 47% of chondroblastomas. The periosteal reaction is usually thick, solid, or layered, and its presence was helpful in distinguishing chondroblastoma from other epiphyseal lesions.

On MRI a chondroblastoma shows low to intermediate signal intensity lesion on T1-weighted images, whereas T2-weighted images show low, high, or heterogeneous signal intensity. Another imaging finding which is important in arriving at the correct diagnosis is the commonly associated bone marrow edema which presents with low signal intensity on T1-weighted images and increased signal intensity on T2-weighted images (Figure 92.3). After intravenous administration of gadolinium the edematous marrow shows enhancement on fat-suppressed T1-weighted images. Edema has also been described involving the soft tissues adjacent to the chondroblastoma. Another sign of inflammation, in addition to the edema in the bone marrow and soft tissues, is the presence of synovitis and joint effusion in the adjacent joint.