I was just reading my report from my scan today and it mentions a small perisac haemotoma. Does anyone know what this is? Should I be concerned?

Before anyone asks, I have rung my ob office and the receptionist asked if I coulld get the report down there today so my ob can check it out and tell me if there are any problems. I'll do that once DD wakes. In the meantime, does anyone have any info or experiences to share?