Case Reports

Wolf in sheep’s clothing: metatarsal osteosarcoma

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References

Metatarsal bones are an unusual subsite for small bone involvement in osteosarcomas. This subgroup is often misdiagnosed and hence associated with significant treatment delays. The standard treatment of metatarsal osteosarcomas remains the same as for those treated at other sites, namely neoadjuvant chemotherapy followed by surgery and adjuvant chemotherapy. Limb salvage surgery or metatarsectomy in the foot is often a challenge owing to the poor compartmentalization of the disease. We hereby describe the case of a young girl with a metatarsal osteosarcoma who was managed with neoadjuvant chemotherapy and limb salvage surgery.

Introduction

Osteosarcomas are the most common primary malignant bone tumor in children and adolescents. Although predominantly occurring in pediatric and adolescent age groups, bimodal distribution (with a second incidence peak occurring in the sixth and seventh decades) is not uncommon. 1 Osteosarcomas of the foot and small bones represent a rare and distinct clinical entity. This must have been a well-known observation for years that led to Watson-Jones stating, “Sarcoma of this [metatarsal] bone has not yet been reported in thousands of years in any country.” 2 The incidence of osteosarcomas of the foot is estimated to be from 0.2% to 2%. 3

These tumors, owing to their rarity, often lead to diagnostic dilemmas and hence treatment delays. 4 They are usually mistaken for inflammatory conditions and often treated with—but not limited to—curettages and drainage procedures. 5 The following case of osteosarcoma of the metatarsal bone in a young girl highlights the importance of having a high index of clinical suspicion prior to treatment.

Case Presentation and Summary

A 10-year-old girl visited our outpatient clinic with a painful progressive swelling on the dorsum of the left foot of 2 months’ duration. There was no history of antecedent trauma or fever. Physical examination revealed a bony hard swelling measuring around 5 x 6 cm on the dorsum of the left foot around the region of the second metatarsal. There was no regional lymphadenopathy or distal neurovascular deficit. She was evaluated with a plain radiograph that demonstrated a lytic lesion in the left second metatarsal associated with cortical destruction and periosteal reaction (Figure 1) . A subsequent magnetic resonance image (MRI) revealed a bony lesion destroying part of the left second metatarsal with cortical destruction and marrow involvement and affecting the soft tissue around the adjacent third metatarsal (Figure 2) . Needle biopsy showed chondroblastic osteosarcoma. Computed tomography (CT) of the thorax and bone scan were both negative for distant metastases.

She received 3 cycles of a MAP (highdose methotrexate, doxorubicin, and cisplatin) regimen as neoadjuvant chemotherapy. Response assessment scans showed partial response (Figures 3A and B) . We performed a wide excision of the second and third metatarsal with reconstruction using a segment of non-vascularized fibular graft as rigid fixation (Figure 4) . The postoperative period was uneventful. She was able to begin partial weight bearing on the fourth postoperative day and her sutures were removed on the twelfth postoperative day. She received adjuvant chemotherapy following surgery. The final histopathology report showed residual disease with Huvos grade III response (>90% necrosis) with all margins negative for malignancy (Figure 5). At present, the child is disease-free at 5 months of treatment completion and is undergoing regular follow-up visits.

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