Fluid-fluid levels result from 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 the tumors with this imaging sign.
Keywords: Fluid-fluid levels, imaging, differential diagnosis, bone tumors, soft tissue tumors, prognosis.
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