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.