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The prevalence and diagnostic significance of fluid-fluid levels in focal lesions of bone

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To determine the prevalence and diagnostic significance of fluid-fluid levels (FFLs) in focal bone lesions.

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Clinical and radiological details of 738 consecutive patients referred with focal lesions of bone and who had undergone MRI were reviewed. FFLs were identified in 83 (11.2%). The proportion of the lesion occupied by FFLs was estimated, based on imaging in all available planes, as <1/3, 1/3–2/3, >2/3 but not the entire lesion, and complete. The degree of FFL change in each lesion was correlated with the final diagnosis, which was either histological (n=80) or clinicoradiological (n=3). There were 31 female and 52 male patients, mean age 25.5 years (range 5–83 years).


Histology revealed 46 benign, 32 malignant and 2 non-neoplastic lesions. A clinicoradiological diagnosis was made in the 3 lesions without histology: 2 were benign (simple bone cyst and intraosseous lipoma) and 1 malignant (a metastasis). Malignant neoplasms commonly showed FFLs which occupied <1/3 of the entire lesion (n=22/32, 68.8%), and 50% of all the lesions in this group were conventional intramedullary osteosarcomas (n=16). With increasing FFL change, malignancy became less frequent: with >2/3 (but incomplete) FFL change, 81% (n=13/16) of tumours were benign. If the entire tumour showed FFL change, the histology was benign in 100% (n=11).


The extent of FFLs within a focal bone lesion appears to be inversely related to the degree of malignancy. If at least 2/3 of the lesion shows FFL change, 89% of diagnoses are benign.

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O’Donnell, P., Saifuddin, A. The prevalence and diagnostic significance of fluid-fluid levels in focal lesions of bone. Skeletal Radiol 33, 330–336 (2004).

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