Complete remodelling post-intralesional resection of an aggressive proximal humerus aneurysmal bone cyst mimicking telangiectatic osteosarcoma.

We describe a case of an aggressive proximal humerus aneurysmal bone cyst (ABC) mimicking telangiectatic osteosarcoma with complete remodelling and reconstitution of the bone. A boy in middle childhood presented with a pathological fracture preceded by progressive right shoulder pain and swelling. Imaging and open biopsy supported the diagnosis of primary ABC with positive ubiquitin-specific protease 6 gene fusion. Treatment was initially refused, leading to significant bone erosion. Subsequently, intralesional resection and grafting were performed, confirming the ABC diagnosis. Three years post-surgery, radiographs show excellent bone remodelling, with the child maintaining premorbid shoulder function. By performing an intralesional resection, there was no doubt of tissue representation, and it allows contamination to be minimised should a wide resection be necessary later. Interestingly, there was complete reconstitution and remodelling of the proximal humerus; likely from intact periosteum like that seen in the donor sites of fibula strut grafts.