Ewing Sarcoma After Treatment of a Unicameral Bone Cyst of the Proximal Part of the Humerus

Unicameral bone cysts (UBCs) were first described by Virchow in 18761. They are commonly found in the proximal part of the humerus in males between eleven and twenty years of age2,3. While some cysts are discovered incidentally after radiographs are taken for other reasons, most patients present with arm pain, with or without fracture through the cyst2. In clinical situations consistent with UBC of the proximal part of the humerus, radiographs are sufficient for diagnosis, and additional imaging usually is not recommended4. The patient and his parents were informed that data concerning the case would be submitted for publication, and they provided consent. A nine-year-old boy had experienced left shoulder pain after playing football. Because the pain had persisted, his primary care provider had obtained a radiograph; this radiograph had demonstrated a cystic lesion of the proximal part of the left humerus without fracture (Fig. 1). Subsequent magnetic resonance imaging (MRI) had been consistent with a benign bone cyst, which was likely a UBC (Fig. 2), without an associated soft-tissue mass. He had been referred to an orthopaedic oncology surgeon for management, and he had been followed for six months as the pain resolved. Fig. 1 At presentation, the anteroposterior radiograph was consistent with a UBC. Coronal short tau inversion recovery ( Fig. 2-A ), coronal T1-weighted ( Fig. 2-B ), coronal T2-weighted ( Fig. 2-C ), and sagittal T2-weighted ( Fig. 2-D ) MRI at presentation did not show a soft-tissue mass. Fig. 2-A Fig. 2-B Fig. 2-C Fig. 2-D Twelve months after the original presentation, the arm pain had returned. After repeat radiographs had confirmed an unchanged benign bone cyst, surgical aspiration and injection of autograft bone marrow and demineralized allograft bone matrix had been performed. At the time of contrast dye injection into the cyst, intraoperative fluoroscopy had not shown a noteworthy soft-tissue mass, thus confirming the diagnosis of UBC (Fig. 3). Fig. 3 Intraoperative fluoroscopic image of the humerus. Twelve months after the injection, follow-up radiographs had shown healing of the cyst. The patient …