DISCUSSION: Postoperative and post-procedural hematomas occur frequently. The ultrasonographic appearance of hematomas differs depending on the amount of time elapsed since the bleeding occurred. In the acute stage, a hematoma appears heterogeneously hypoechoic; representing uncoagulated (liquid) blood and the beginning interface between clots and fibrin strands. As the clotting process progresses, the hematoma becomes progressively hyperechoic; appearing as an irregularly marginated, complex, cystic mass with thickened hyperechoic walls or irregular internal septations. A chronic hematoma may be anechoic or isoechoic, hypoechoic or mildly echoic with a subtle fluid/debris level. Additional sonographic signs associated with hematomas are the “plankton sign” and the “hematocrit sign”. The “plankton sign” is a dynamic movement of protein or cellular debris within the hematoma due to respiratory or cardiac movements. The “hematocrit sign” is the layering deposition of cellular debris and is visualized as a gradient of echogenicity.