Problem : curves in my mesh

I had retopologies a human sculpting but some curves are inserted in my mesh and modify it.
My mesh in edit mode :

My mesh in object mode :

My mesh after AltC converting mesh to curve :

How can I delete those curves in my mesh ? I have already try to AltC curve to mesh but it do not seems to do anything and I have try to export in .obj or .stl and reimport but it reimport empty files.

In waiting for your answers