This can involve a breast implant or a muscle flap.

 

With an implant a silicone sack filled with either silicone gel or saline (salt water) is inserted underneath your chest muscle and skin. Before being inserted, the skin will sometimes need to be stretched to the required breast size. This is done by placing an empty bag where the implant will finally go, and gradually filling it with saline over weeks or months. The bag is then replaced by the implant in another operation.

 

The muscle flap technique involves using a flap of your own muscle (eg the latissimus dorsi muscle that runs under your arm) that is rotated into the space where the breast used to be.  A nipple reconstruction is usually undertaken at a later date.