Inflatable balloon for creating an anatomical space between tissue layers

An inflatable balloon for creating an anatomical working space between tissue layers in a body, said balloon comprising: two panels fused together along a seam extending around a periphery of said panels thereby defining an inflatable space within said panels, said seam being inverted into said inflatable space, said balloon thereby having at least partially reentrant outer edges; said two panels defining a proximal sleeve for insertion of a tunneling member; and an inflation lumen communicating with said inflatable space for inflating and deflating said balloon between inflated and collapsed conditions, said inflation lumen fused onto only one of said panels at a position distal to said proximal sleeve.