Atlas of Signs in Musculoskeletal Radiology is approved by the ARRS (American Roentgen Ray Society) and is included in AJR Webreview

A. Gentili,MD, M. Beller, MD, S. Masih, MD, L.L. Seeger, MD

Diagnosis:

Aneurysmal bone cyst

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.

References:

Atlas of Signs in Musculoskeletal Radiology is approved by the ARRS (American Roentgen Ray Society) and is included in AJR Webreview

A. Gentili,MD, M. Beller, MD, S. Masih, MD, L.L. Seeger, MD