Fig. 9

Aneurysmal bone cyst. Lateral radiograph (a) of the cervical spine demonstrates a large, osteolytic, expansile mass arising from the C2 vertebral body, resulting in significant bony remodeling. The mass is sharply defined and demonstrates thin sclerotic margins, also known as an “eggshell cortex” (orange arrows). Sagittal CT image of the cervical spine (b) confirms the lesion within the C2 vertebral body. Axial CT image in the soft tissue window (c) shows fluid-fluid levels (orange arrows), compatible with hemorrhage. Axial CT image in the bone window (d) shows near complete obliteration of the posterior arch with some areas of remnant thin sclerotic rim, "eggshell cortex" (white arrow)