What Does Cavum Septum In An Ultrasound Indicate?

What is Corum Septum? My wife and I are a little over five months along and we just had a 3D ultrasound done yesterday. Our child s doctor said that she has a minor issue with her brain. A nerve hasn t fused completely. I need to know what exactly this means and what are we going to be expecting later in life when she is born. Our next appointment is set for two weeks from now.