Challenges in Diagnosing Diaphyseal Osteosarcoma - Importance of Strong Clinical Suspicion and Biopsy Technique: An Illustrative Case Report

Abstract

Introduction: Osteosarcoma is the most common primary malignant bone tumor in adolescents, typically affecting the metaphyseal region of long bones. Diaphyseal osteosarcoma is rare and often mimics benign conditions such as osteomyelitis, leading to diagnostic delays.

Case report: A 17-year-old boy presented with progressive left thigh pain and swelling for 3 months. He had a trivial injury to left thigh 7 months back while playing kabaddi. Initial radiographs, computed tomography (CT), and magnetic resonance imaging showed a lytic intramedullary lesion with cortical thickening, suggestive of osteomyelitis. CT-guided biopsy also revealed features consistent with chronic osteomyelitis. Later debridement with open biopsy confirmed increased reactive osteoclastic giant cells, suggestive of chronic healed osteomyelitis. Despite empirical antibiotic treatment, symptoms worsened. A second open biopsy with intraoperative frozen section (FS) revealed features of high-grade osteosarcoma. Histopathological confirmation and immunohistochemistry with SATB2 established the diagnosis. The patient was treated with neoadjuvant chemotherapy followed by resection and femur reconstruction with a custom prosthesis.

Discussion: This case illustrates the diagnostic pitfalls associated with diaphyseal osteosarcoma, especially in post-traumatic settings. It has also been observed in previous research studies that early overlapping clinical and radiological features with osteomyelitis often result in misdiagnosis. Needle biopsies, while minimally invasive, may yield non-representative samples, especially in heterogeneous tumors. Open biopsy targeting the lesion's transition zone, supported by intraoperative FS, enhances diagnostic accuracy and enables timely intervention.

Conclusion: In atypical presentations of musculoskeletal pain and swelling unresponsive to conservative treatment, malignancy should be suspected. A multidisciplinary approach, early advanced imaging, and appropriately planned biopsies are critical for accurate diagnosis and effective management of osteosarcoma.

Keywords: Osteosarcoma; computed tomography-guided biopsy; frozen section; open biopsy; osteomyelitis.

Figure 1

Presenting X-ray of left femur shows features of an osteolytic intramedullary lesion at the junction of the middle and distal third with surrounding sclerosis and periosteal reaction.

Figure 2

Computed tomography of the left thigh shows a lytic intramedullary lesion with cortical thickening and a solid periosteal reaction (axial and coronal sections).

Figure 3

Magnetic resonance imaging of the left thigh shows a lytic intramedullary lesion with cortical thickening and a solid periosteal reaction in the proximal middle third junction of the femur in the coronal section.

Figure 4

Computed tomography-guided biopsy.

Figure 5

Intraoperative image of open biopsy done through a cortical defect enlarged to a window at the site of the lesion

Figure 6

H and E ×100 shows areas of necrotic bone with scattered chronic inflammation, necrotic bone, focal fibrosis, and osteoclastic giant cells.

Figure 7

Repeat magnetic resonance imaging of the left femur shows a lytic-sclerotic lesion with a calcific extraosseous soft tissue component with aggressive periosteal reaction in coronal and axial sections .

Figure 8

Frozen section sample taken from the transition zone .

Figure 9

H and E ×200 – Frozen section – Shows atypical cells with increased mitosis.

Figure 10

H and E ×400 shows atypical cells with osteoid formation surrounded by malignant osteoblasts.

Figure 11

Immunohistochemistry ×200 for SATB2 positive in the tumor cells.

Figure 12

Post-operative X-ray of left femur reconstruction with custom mega prosthesis.