Teaching Case

A 66-year-old man was referred to our hospital with a slow-growing mass on his left leg. He did not report pain, weakness or weight loss. The mass was firm and the skin was intact.

Ultrasound images show a 5 cm soft tissue mass located in the deep tissues subjacent to the superficial fascia (Fig. 1a). It appears to be densely calcified. Colour Doppler does not detect intralesional blood flow, probably due to the extensive calcification (Fig. 1b).

Conventional radiographs show a large soft-tissue mass and confirm extensive calcification (Fig. 2a, b). CT shows small, granular, streaky and amorphous calcification located in the center of the mass (Fig. 3a, b).

On MR images the central calcified area, with low intensity on both T1WI and fat-saturated DP-WI sequences, may be appreciated. The unmineralised peripheral area shows low-intermediate intensity on T1WI and high signal on fat-saturated PD-WI (Figs. 4a-d). Contrast-enhanced MRI exhibits peripheral, nodular and heterogeneous enhancement (Fig. 4d).

Extraskeletal mesenchymal chondrosarcoma (EMC) is a rare malignancy characterised by a biphasic histologic pattern of small undifferentiated round cells and islands of well-differentiated cartilaginous matrix. It represents about 2% of all soft-tissue sarcomas [1]. The three histologic types are myxoid, mesenchymal, and low grade, which is much less frequent.

Epidemiologically, the myxoid subtype is more frequent in men around 50 years of age, whereas the mesenquimal subtype is more prevalent in young adult women [1].

Clinical presentation is nonspecific, presenting frequently as a slow-growing painless mass. In this clinical setting, radiography and ultrasound are usually the first tests requested in our institution. Depending on the findings, subsequent MRI and/or CT will be performed.

Calcification is present in about 67% of the cases [2]. Ring and arc or granular mineralisation is an important diagnostic sign, therefore CT is useful in the diagnosis, allowing analysis of the mineralisation pattern.

MRI allows to exclude fatty component and bone and vascular involvement. MRI appearance depends on the degree of calcification of the lesion.
The non-mineralised area is usually isointense on T1WI and of high to intermediate intensity on T2WI, whereas the calcified zone has low intensity on both sequences. A diffuse heterogeneous enhancement, suggesting abundant blood flow, has been reported both in the calcified and non-calcified areas [2, 3].

The differential diagnosis of EMC includes extraskeletal osteosacoma (EO), synovial sarcoma, myositis ossificans and undifferentiated pleomorphic sarcoma (malignant fibrous histiocytoma).
Dense cloud-like calcification instead of ring-and-arc mineralisation helps to distinguish EO from EMC .
Myositis ossificans usually shows rim or peripheral mineralisation after 4-6 weeks and demonstrates areas of fatty infiltration between bone trabeculae [4].
It is difficult to distinguish synovial sarcoma and undifferentiated pleomorphic sarcoma from EMC. Both of them may show erosion or invasion of adjacent bone. Synovial sarcoma usually is located around the joints [5].

Final diagnosis needs a histological confirmation, in our case an excisional biopsy was performed.

The recommended treatment of EMC is resection with wide surgical margins. The effectiveness of chemotherapy and radiotherapy remain poorly defined [6].

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