It's probabably a two piece stem used in mono-block water-tight cases, Mido used to have a tool that would go in between the crown and the case like a wedge and pull the crown and part of the stem out it also had a syringe-like pump that it will connect to the stem's tube(once the crown was out)and push air into the case and the crystal would pop-out, turn the case over and the movement and dial will come out. In the absence of a specific Tool, you can try sliding a soft metal or plastic tweezer(so no to scratch the case) in between the case and the crown and wedge the crown out. There are great chances of breaking the stem specially if the two parts are corroded together.

Albert A.