Ewing's sarcoma presenting as a solitary cyst

Ewing sarcoma of the tibia mimicking fibrous dysplasia

Ewing sarcoma (ES) family of tumors is the second most common primary bone malignancy in children. It usually presents as an aggressive looking lesion often located in the meta-diaphyseal region of long bones, with bone destruction, permeation, cortical thinning and/or destruction, periosteal reaction, and large soft-tissue mass. The purpose of this study is to illustrate the occurrence of a fibrous dysplasia (FD)-appearing ES of the tibia. These cases underscore the potential difficulties encountered in the diagnosis of ES. In this study, we performed a retrospective review of children who presented with an otherwise benign-appearing lesion of the tibia, suggestive of FD, which proved to be ES after biopsy. As a result, all patients presented with a history of indolent lower extremity pain of several months of duration, without significant swelling or constitutional symptoms. Plain films revealed an otherwise benign-appearing/FD-like lesion without bone destruction and mild cortical thinning, little or no periosteal reaction. Magnetic resonance imaging revealed the intramedullary extension of the lesion without significant cortical or periosteal involvement and no soft tissue mass. Lesions were hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging. All patients underwent open incisional biopsy and after cytogenetic and molecular studies, the diagnosis of ES was confirmed. We conclude that ES is a deadly malignant tumor if left untreated or if mismanaged. Although it usually presents as an aggressive-looking lesion, at times it may mimic FD and has a benign-looking appearance, making the diagnosis unlikely and challenging. Summation of these cases demonstrates that the potential reasons for misdiagnoses include a low level of suspicion, an atypical site occurrence, a benign radiographic appearance, and a lack of or insufficient histologic specimens.

Magnetic resonance imaging of hip tumors

After initial evaluation with radiography, magnetic resonance (MR) imaging is the most common modality used to establish the diagnosis and characterize osseous and soft tissue tumors of the hip. Tumors involving the proximal femur are often benign, and MR imaging can be specific in diagnosing solitary bone cyst, osteochondroma, and chondroblastoma. Benign and malignant soft tissue tumors about the hip are often nonspecific in their MR imaging appearances, but knowledge of the patient's age may direct a more limited differential diagnosis. In the setting of malignancy, MR imaging is commonly used to stage tumors and follow patients postoperatively.