Fluid-fluid levels in bone tumors is a commonly encountered finding, both in benign as well as malignant bone tumors, and can be used to differentiate between the two.
Method of assessment
On the sagittal T2W image:
- measure the length of the largest fluid-fluid level (A)
- measure the maximum length of the tumor (B)
- calculate A/B ratio
- an A/B ratio >41.5 means the tumor is more likely to be benign
- an A/B ratio <41.5 means the tumor is more likely to be malignant
The rationale behind this unique method of assessment is that areas of necrosis in a malignant tumor are more likely to result in multiple small fluid-fluid levels as compared to a benign tumor.