AutoCAD .NET :: How To Test For Existence Of Self Intersecting 2D Polylines

Im trying to write a routine in VB.net based on Fenton's examples from 'Zero to 3D in 60 Minutes'. the routine uses a filter set to select all 2D polylines in a document then a test is needed for each polyline to establish whether it is a loop, which can then be extruded into a solid or it is a non loop, where the operation will need to be an extruded surface, or if the polyline is a non-loop.

So far my code will pick up every 2D polyline and try and extrude it, but i need to catch the non-looped entities to handle them with an extrude surface method or if self-intersecting polylines, to either drop them and not cause an exception or process them in another way.

What entity attributes or methods should I use to perform testing to establish this loop and non-loop existance of the polylines to achieve this. I work with both C# and VB.net.