Discussion | Single axial section of a knee CT which reveals an aneurysmal bone cyst in the left distal femur with a fluid-fluid level. The fluid-fluid level sign is by no means pathognomonic, but is helpful in narrowing the differential. The sign is produced by a cystic lesion with water density fluid layering atop blood. The fluid-fluid level is often seen in aneurysmal bone cysts, but it may also be seen in giant cell tumor, telangiectatic osteosarcoma, and chondroblastoma. |
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