Painful left thigh mass

The patient lived alongside dogs and sheep on a rural Greek farm until he was a teenager. Seventeen years before presentation he emigrated to the United States. The radiographic findings of a lytic bone lesion with cortical destruction, scalloping, and periosteal reaction suggested a primary bone tumor (Fig. 1 in the case presentation). After MRI, chondrosarcoma and sarcoma with necrosis were suspected because of the regions of fluid-like signal intensity within the large soft tissue mass (Fig. 2 in the case presentation). Although echinococcal cyst was also considered, this diagnosis was incorrectly dismissed because the patient had not been on a farm for over 30 years. Therefore, the potential for disease spread and anaphylaxis were not considered prior to biopsy. Percutaneous CT-guided 14-gauge needle biopsy targeted the vastus lateralis to enable needle track resection at surgery. Aspirated fluid and cyst wall fragments were diagnostic of hydatid disease (HD) from Echinococcus granulosus. Radical resection of the soft tissue component with debridement of the femur was performed. Low power histological evaluation showed the hydatid cyst and daughter vesicles with central clear areas that had contained primarily fluid, as well as the perihydatidic adventitia (host response; Fig. 3 in the case presentation). Higher magnification demonstrated the laminated echinococcal membrane and multinucleated giant cells in the adventitia (Fig. 3 inset, in the case presentation). Three years after resection, there was local recurrence with a pathological femoral fracture. Treatment included wide excision requiring proximal femoral replacement with a megaprosthesis total hip arthroplasty. Now, 7 years later, the patient is functioning well without assistive devices and with no recurrence. On radiographs, osseous HD may mimic an aggressive primary or secondary bone tumor, bacterial osteomyelitis, or fibrous dysplasia with coarse trabeculation, sclerosis, bone expansion, erosion, cortical destruction, and osteolysis [1, 2]. MRI may demonstrate characteristic round structures, daughter vesicles, within the mother cyst that are lower signal intensity on T1-weighted images with no enhancement after contrast medium administration, a finding helpful in the diagnosis (Fig. 2 in the case presentation) [1, 2]. The younger daughter vesicles appear darker on T1-weighted images because they contain more pure fluid and fewer protoscoleces than the mother cyst [3]. While the “rim sign,” a thick dark cyst wall on T2-weighted images, is characteristic at other sites [4], it is not as specific a finding in muscle. After contrast medium administration, the perihydatidic layer typically enhances [1] (Fig. 2c in the case presentation). Hydatid disease, which occurs in endemic areas worldwide, has a well-described life cycle [5–7]. Dogs are The case presentation can be found at doi: 10.1007/s00256-013-1634-3. F. A. Sakamoto : C. S. Winalski (*) Imaging Institute, Cleveland Clinic, 9500 Euclid Avenue, A21, Cleveland, OH 44195, USA e-mail: winalsc@ccf.org