The fluid collection inside a bursa is usally seen as hypo-anechoic layer with B-mode ultrasound scan, right?…..Wrong!

The Wikipedia definition of a synovial bursa: “A bursa (plural bursae or bursas) is a small fluid-filled sac lined by synovial membrane with an inner capillary layer of viscous fluid (similar in consistency to that of a raw egg white). It provides a cushion between bones and tendons and/or muscles around a joint. This helps to reduce friction between the bones and allows free movement. Bursae are filled with synovial fluid and are found around most major joints of the body.”

The ultrasound appearance depends on the moment in wich you make the examination; especially in acute conditions, if a blood component is present within the bursa, it appears as an isoechoic layer.

Superficial retrocalcaneal bursa of a professional football player – GE Stir sagittal Mri scan (0.3 T) – US sagittal scan. Note the different appearance of the fluid collection between Mri and ultrasound scan. The Mri also shows a small bone marrow edema of the calcaneal posterior process.

The Elastosonography evaluation in this case works like a “contrast agent”, well depicting the fluid collection within the bursa (red/soft).