Teaching Case

An 81-year-old female consults for a 4-month mass and functional limitation in the right shoulder without any other associated symptoms. No traumatic background associated. The physical exam showed a petrous mass attached to the deep planes on the posterolateral surface of the shoulder.

CT (Figures 2a, 2b and 2c) and MRI (Figures 3a, 3b, 3c, 3d, 3e and 3f) of the right shoulder show a polylobulated bone mass centred in the metaphyseal-diaphyseal region of the right proximal humerus with a lytic, expansive and infiltrative appearance, high T2-signal, mild restriction on diffusion sequence and rim-enhancement. Intralesional chondral calcifications have rim enhancement as well. It produces insufflation with deep endosteal scalloping and extrusion of the soft tissue component at different points of the tumour. There is also an intramuscular soft tissue tumour component, with similar signal and morphological features located at the right triceps, with a small calcified tubular connection at the lower margin of the tumour, which connects it to the intramedullary component of the bony component. Both bone and intramuscular tumour components present progressive contrast uptake that is concentrated mainly in the margins.

Retrospectively, in a 2017 chest X-ray (Figure 1), an intramedullary lesion with chondroid calcifications was observed in the location of the lytic bone tumour, suggestive of enchondroma.

Chondrosarcoma is the second most common malignant primary osseous neoplasm in the adult skeleton [1], with a male predominance and a peak incidence between 30 and 65 years [4]. It can be primary or secondary depending on a preexisting neoplasm, such as enchondroma [1]. Malignant transformation of the enchondroma is unusual, being more commonly seen in the proximal long tubular bones and axial skeleton [1]. It may rarely develop extraosseous lesions or even arise within the synovium [4].

Enchondroma is commonly an incidental finding, while chondrosarcoma has an insidious and progressive clinical presentation, with night-aggravated pain present for months to years, associated with a palpable mass. The definitive diagnosis and staging are made with histological and imaging findings [5]. Imaging findings reveal lobular lytic lesions with variable amounts of mineralised matrix and poorly defined margins. A calcified mineral matrix can be appreciated in up to 75% of cases, being more amorphous or stippled in less well-differentiated lesions. Other findings are extensive endosteal scalloping, periosteal reaction and expansile bone-remodelling, cortical destruction and soft tissue mass.

MR offers the best method for characterisation of the extent of marrow involvement. On T1-weighted images, the lesion is low to intermediate in signal. The non-mineralised chondroid matrix is a high signal on T2-weighted images, and individual lobules are separated by lower-intensity fibrovascular septae. Trapped areas of marrow presenting as punctate areas of high signal on T1-weighted images are less frequently seen than with enchondroma and, when seen, suggest that the chondrosarcoma may have arisen from an underlying enchondroma.

Peritumoral oedema, particularly when extensive, has also been reported to increase the likelihood of a malignant diagnosis [1]. Differential diagnosis is especially in the differentiation between a benign chondroma and a low-grade central chondrosarcoma. Radiographic features such as proximal location or axial skeleton location, size greater than 5cm, lobulated aspect, ill-defined margin, endosteal erosion and bone destruction with extra-osseous component suggest a malignant lesion. Chondromyxoid fibroma, chondroblastoma or giant cell tumour are other differential diagnoses [2].

The therapeutic approach for chondrosarcomas is determined by the location and histologic grade. Surgical excision is the primary treatment. Chemotherapy may play a role in dedifferentiated chondrosarcoma containing high-grade spindle cell components. Chondrogenic tumours are generally considered radioresistant; however, it can be administered after incomplete resection of high-grade conventional or mesenchymal chondrosarcomas for curative purposes [3].

Take Home Messages

• Chondrosarcomas are the second most common malignant primary bone tumour.
• It may be primary, and, less frequently, secondary from a previous bone tumour, such as enchondroma.
• Clinical and radiological features help in the differentiation between a benign chondral neoplasm and a chondrosarcoma.
• The therapeutic approach is determined by location and histologic grade, being surgical excision the primary treatment.

All patient data have been completely anonymised throughout the entire manuscript and related files.