An adhesion is when an incision in the process of healing binds to the layer behind it when it's not supposed to. In this case, it appears the skin/surface fat bound to the larynx while healing. I suspect this could be cause if there is no movement between the two layers during healing giving the body time bind where it's not supposed to. Exactly how the two can be separated, I am not sure but maybe you can work the skin with your hand to break the binding.