What Is Meant By Extrusion Of Mirena Coil?

Extrusion of mirena coil?I had mirena coil inserted october 2010.At my follow up consultation 6 wks later my gynaecologist could not locate coil on scan.I hence had a laparoscopy yesterday and coil could not be found. Explanation I was given was that I had probably passed the coil while urinating.Is this possible and if so is it possible I passed coil without feeling anything ?