PMC3805425_01
(a, b) Anteroposterior radiographs of the proximal femur and right hip showing radiolucent cystic lesions with sclerotic margins and no periosteal reaction, findings in keeping with fibrous dysplasia (straight arrows)
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Conventional X-rays of the right femur demonstrated a 9.5 x 3.3 cm intra-osseous cystic lesion with sclerotic margins at the right femoral neck in the subtrochanteric and metaphyseal region (Fig. 1a). A similar lesion was observed within the right ileum above the acetabulum (Fig. 1b).
(a) Coronal STIR, (b) T1, and (c) T1-weighted with fat-sat and gadolinium (Gd) contrast agent MR images. Bony lesions with high signal on STIR, low signal on T1, and heterogeneous contrast enhancement after Gd injection (straight arrows) can be observed. Soft tissue lesions with high signal on STIR, low signal on T1, and a mixture of rim and central contrast enhancement after Gd injection (curved arrows) can also be observed
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The bony lesions were typical of fibrous dysplasia, but the diagnosis of the soft tissue lesions was uncertain, including differentials such as soft tissue sarcoma, lymphoma, and neurofibroma (Fig. 2).   
18F-FDG PET/CT. (a) Coronal CT with a bone window showing multi-loculated expansile intramedullary fibrous dysplasia lesions in the ileum and proximal part of the femur (straight arrows). (b) Fused PET/CT with increased FDG uptake (SUVmax 7.0) only in the lower region of the fibrous dysplasia lesion in the right ileum (curved arrow). Notice that the region of the fibrous dysplasia taking up the FDG corresponds to the region on the coronal MR image in Fig. 2c that is the most enhanced by the Gd contrast agent. (c) Coronal CT with a soft tissue window showing the low-density myxomas in the medial thigh muscles (curved arrow). (d) Fused PET/CT showing slightly increased FDG uptake in the myxomas (curved arrow)
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The areas with FDG-uptake on the PET/CT also showed contrast enhancement on the MRI with intravenous gadolinium (Figs. 3 and 4).
MRI and 18F-FDG PET/CT. (a) Axial T2-weighted MR image with high signal, partly cystic-appearing soft tissue lesion in the medial thigh muscle (straight arrow). (b) Axial T1-weighted MR image after intravenous Gd agent administration with contrast enhancement of the more solid-appearing region of the myxoma (straight arrow). (c) Axial CT with a soft tissue window showing the low-density, almost cystic-appearing lesion in the medial thigh muscle (straight arrow). (d) Fused PET/CT with slightly increased FDG uptake (SUV max 2.1) in the apparently more solid region of the myxoma. Notice that the region of the myxoma taking up the FDG corresponds to the Gd-enhanced region on the MRI (straight arrow)
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The areas with FDG-uptake on the PET/CT also showed contrast enhancement on the MRI with intravenous gadolinium (Figs. 3 and 4).
Typical histological appearance of intramuscular myxoma: well-circumscribed, paucicellular lobulated myxoid tumour with skeletal muscle involvement
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Histological examination of the lesion supported the radiological diagnosis of myxoma (Fig. 5).