ABC in the clavicle resembling a solitary bone cyst in MRI
An 8-year-old girl with painless swelling on the right clavicle was found to have a mass of 2 cm × 2 cm in the right supraclavicular region on the physical examination. In the radiographs taken for the mass, in the right clavicle was found eccentrically located, septated, superior cortex thinned but undisturbed an expansile lytic lesion with slightly heterogenous internal structure. On CT in the right clavicle, expansile, heterogeneous bone lesion in the right clavicle was obtained. It was noted that a portion of the lesion was surrounded by a sclerotic line and the cortical cortex was somewhat tapered in CT sections.

A focal septation-like appearance was observed in the lesion. On MRI the lesion in the right clavicle was seen a thin septation in the central portion and expansile character low signal on T1 weighted images and high signal and in the T2 weighted images (Figure 3 A and B). In contrast enhanced images the lesion showed peripheral contrast enhancement, but not a significant fluid-fluid level (Figure 4). Despite the eccentric and septated appearance on x-ray examination, the presence of highly homogeneous of internal structure and absence of fluid-fluid levels on CT and MR, suspicious in terms of solitary bone cysts.

The presence of focal, more contrasting areas within the lesion in MR images also suggests the differential diagnosis of telangiectatic osteosarcoma. Aspiration biopsy was performed first for the differential diagnosis of the lesion, followed by biopsy of the lesion. Aspirated red liquid was prepared using a liquid based cytology method. Cytology was the result of blood elements (non-diagnostic cytology). There were no signs of infection. In the biopsy specimen, the material was mostly composed of reactive new bone tissue and a very small area of lesion support the ABC (Figure 5).

The case was operated with prediagnosis of ABC. Frozen study showed numerous myxoid and chondroid stromal cartilaginous tissue and loose stromal component and membranous fragments between them and no definitive diagnosis was made. In the resected curette material, fibrotic stroma surrounding blood-filled cavities, hemosiderin-loaded macrophages and osteoclastic giant cells were observed. The case was reported as ABC. Cellular atypia and other malignancy findings were not observed in the material. The lesion was curetted during surgery and the space in the clavicle was filled with bone graft.

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