Deformed uterus. Coloured 3-D ultrasound scan of a patient with a septated uterus. The uterus lumen is the Y-shaped region at centre, surrounded by the endometrial lining (dark). A septated uterus forms during embryonic development, when the two ducts that are precursors to the uterus fail to fuse properly. This leaves a strip of tissue along the middle of the uterus (septum), partitioning it. Ultrasound is a diagnostic technique that sends high frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure. 3-D ultrasound uses computer technology to return more detailed images than conventional 2-D scans.