Telangiectatic osteosarcoma versus aneurysmal bone cyst: a diagnostic challenge on small biopsy

Telangiectatic osteosarcoma (TOS) is a rare malignant bone tumor that closely resembles benign conditions, such as aneurysmal bone cysts (ABCs), both radiologically and clinically, leading to potential diagnostic confusion. The misdiagnosis can result in inappropriate treatment, making accurate differentiation crucial. A 28-year-old male presented with swelling around the left knee. Imaging studies revealed an expansile, lobulated lesion in the tibia, initially suggestive of an ABC. However, histopathological examination showed blood-filled cystic spaces and irregular osteoid formation surrounded by malignant osteoblasts, consistent with TOS. Immunohistochemical staining with special AT-rich sequence-binding protein 2 and S100 further supported the diagnosis. The significant overlap in imaging features among TOS, ABCs, and giant cell tumors underscores the importance of histopathological evaluation for a definitive diagnosis. Early and precise identification of TOS is essential to ensure proper treatment and improve patient outcomes. This case highlights the diagnostic challenges of differentiating TOS from ABCs and emphasizes the crucial importance of histopathological and immunohistochemical analysis in making an accurate diagnosis.