Calcaneal Osteosarcoma

A 53-year-old man presented to an orthopaedic department with a history of left ankle pain over the past 3 weeks with swelling that worsened with activity and in the morning. No trauma was reported. The laboratory markers of inflammation were not elevated. At physical examination moderate swelling of the ankle without notable impact on range of motion was observed.

No pathological findings were observed on X-ray.

CT of the left ankle showed an ill-defined hypodense lesion in the calcaneum with no cortical destruction or periosteal reaction. No calcification or signs of mineralization was observed.

MRI revealed a diffuse hyperintense signal on fat-suppressed proton density-weighted image and diffuse hypointense signal on T1-weighted image of the calcaneus. After contrast administration, heterogeneous enhancement of the calcaneus was observed. There was no evidence of periosteal reaction or extraosseous expansion. Mild oedema of the surrounding soft tissues without ankle joint effusion were observed.

Scintigraphic imaging confirmed the increased uptake of the radioactive substance of the left calcaneus. No signs of tumour spread or metastasis was observed on bone scintigraphy. Thoracic metastases were excluded with additional thoracic CT imaging.

Osteosarcoma is the most common non-haemopoietic primary malignant neoplasm of bone. It typically affects people from 10 to 30 years old, with a peak incidence in the second decade of life, showing slight male predominance [1, 2]. The diaphysis of the long bones are the most common sites where osteosarcoma may arise [1,3]. Osteosarcoma of the foot accounts only for 1% of all osteosarcoma cases [4]. Within the foot it arises from the calcaneus or metatarsal bones in 75% [4]. These cases are more likely to be low grade and have higher reported survival rate [4].

Symptoms of osteosarcoma presentation are non-specific. Progressively worsening pain and swelling in the affected ankle joint are the major complaints. These were observed in our case. Physical examination typically reveals tender swelling and restricted joint mobility [1,4].  Even though NSAID administration causes good initial improvement of symptoms, they are often the cause for delayed diagnosis and treatment [4].

Typical radiograph and CT appearance of the calcaneal osteosarcoma can be very informative, including dense sclerotic, lytic lesion, cortical destruction and extraosseous expansion [1, 5]. In our case no lesion was detected on radiograph, however, CT showed a lytic lesion with no cortical destruction, periosteal reaction, calcification or signs of mineralization. MRI should be performed for preoperative staging and offers good visualisation of extraosseal infiltration [1]. MRI signal of the lesion is usually heterogeneous due to mixture of lysis, sclerosis and rarefaction [1]. Heterogeneous signal on MRI was also observed in our case, on account of necrotic and sclerotic lesions in combination with areas of preserved bone structure. MRI can help in differentiating the tumour, but only histopathology offers definitive diagnosis [1]. Our histopathology exam revealed malignant sarcomatous cells arranged in cords and nests with associated osteoid deposition. Bone scintigraphy is performed in order to rule out osseous metastases [6]. Additionally, CT of the chest ought to be performed to rule out metastatic disease at the time of diagnosis [1, 4].

The treatment of the bone sarcomas varies depending on the stage. Standard treatment of patients with the osteosarcoma consists of a combination of chemotherapy and surgery [4,7]. Limb-salvage surgery of the foot osteosarcoma is usually not possible, due to poor compartmentalisation of the foot. Therefore, as in our case, below the knee amputation is surgery of choice [4]. Currently, the 5-year survival rate of all osteosarcomas after adequate therapy is approximately 60-80%, depending on the tumour’s response to neoadjuvant chemotherapy [1,7].

Teaching points: Although osteosarcoma is one the most common primary malignant tumours of bone, it rarely occurs in the feet. It can be detected on radiograph or CT, but MRI must be performed for preoperative staging. The final diagnosis is made by histopathology examination. Treatment usually consists of a combination of chemotherapy and surgery.

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