The transformation of aneurysmal bone cyst into telangiectatic osteosarcoma: the development of a second tumour or a wrong initial diagnosis?

Aneurysmal bone cyst (ABC) and telangiectatic osteosarcoma (TOS) share a lot of similarities in terms of the initial clinical presentation, the radiological semiotics and even the morphological pattern, however, they are completely different nosological entities requiring absolutely different treatment approaches. This article reports a clinical case of TOS of the femur which developed 1.5 years after the treatment of ABC of the same location and presents an analysis of literature on the differential diagnosis of these diseases, the modern concept of the pathogenesis of ABC and the possibility of the transformation of ABC into TOS. The patient's parents gave consent to the use of their child's data, including photographs, for research purposes and in publications.