Low-grade central osteosarcoma of the hallux with a 7-year undiagnosed course: Case report

Abstract

Low-grade central osteosarcoma usually exhibits a long course with nonspecific symptoms, while the imaging and histological findings may be easily confused with a variety of benign fibroosseous lesions. A 15-year-old boy was referred for a painless swelling of the proximal phalanx associated with shortening of the right hallux. A benign cystic bone lesion complicated by a pathological fracture had been diagnosed on the radiographs at 8 and 10 years of age after sport injuries. He was referred for evaluation and treatment of the bone lesion. Magnetic resonance imaging and computed tomography were performed. A referral centre was contacted, since there was a strong evidence of malignancy. An open biopsy was suggested, which indicated bone malignancy. The patient was then referred to the specialized tumor centre. A new biopsy was performed there, since the previous sampling was considered insufficient or inadequate to secure a differentiation from fibrous dysplasia. It ensured the diagnosis of low-grade central osteosarcoma. Radical excision of the proximal phalanx and reconstruction of the defect with an iliac graft associated with arthrodesis of both the hallux metatarsophalangeal and interphalangeal joints was the treatment of choice. Disturbed wound healing necessitated hardware removal 4 months postoperatively. No further interventions were required in the follow-up. Clinical and radiographic evaluation at 12 years confirmed no evidence of local recurrence or distant metastasis. The patient was satisfied with the final outcome and reported unrestricted participation to physical activities and sports. • The rarity and the highly variable presentation of the foot and ankle malignancies may explain why they are often not considered in the differential diagnosis and the increased likelihood of delayed or incorrect diagnosis. • A low-grade central osteosarcoma localized in the proximal phalanx of the great toe of a 15-year-old boy is presented. The imaging appearance of the lesion was not correctly assessed to suggest a potentially malignant pathology and to require an early bone biopsy leading to a 7-year delayed diagnosis. • All available clinical and imaging features should be carefully considered in decision making, during the diagnostic steps in a patient with a potentially malignant bone tumor of the foot or ankle, to ensure that the diagnosis will not be delayed or missed and that proper treatment by a specialized tumor surgeon in a designated tumor centre will be offered.