Fluid-fluid Levels in Musculoskeletal Tumor Imaging

Fluid-fluid levels result from the separation of two fluids of differing densities within a cavernous space with the boundary between the two layers running in a horizontal plane at 90 degrees to the direction of gravity. Magnetic resonance imaging is the most sensitive imaging modality to identify fluid-fluid levels. Although the most common bone lesions containing fluid-fluid levels are aneurysmal bone cyst and telangiectatic osteosarcoma, fluid-fluid levels can be observed in a wide variety of bone and soft tissue lesions. Therefore, fluid-fluid levels cannot be considered diagnostic of any particular type of tumor and the diagnosis should be made on the basis of other clinical, radiological and pathological findings. This article summarizes the pathophysiology and imaging characteristics of fluid-fluid levels and discusses the differential diagnosis of tumors with this imaging sign.

Automated summary

Fluid-fluid levels in cavernous spaces result from the separation of two fluids with differing densities, with MRI being the most sensitive imaging modality for identification. They are commonly found in aneurysmal bone cysts and telangiectatic osteosarcomas, but can also be observed in a variety of other bone and soft tissue lesions. Diagnosis of tumors with fluid-fluid levels should be based on clinical, radiological, and pathological findings rather than solely on this imaging sign.