Why is nipple sensation more often lost with bilateral mastectomy, but not augmentation?

Bigger operation: Mastectomy involves removing as much breast tissue as possible, either removing the nipple & areola or, occasionally keeping them but scraping as much breast tissue out just underneath. Either of these approaches will disrupt the nerves to that area. With augmentation, no tissue is removed; depending on scar and implant location, it should have minimal effects on the nipple-areolar tissue.