Keyhole is a version of top surgery where a single, small incision is made under the nipple. That incision is used to remove excess interior contents. This surgery is more common among those with smaller chests, due to surgical requirements. The nipple placement is harder to control than it is with other surgeries, however, the nipple stalk is not severed, and sensation is retained.

YouTube Video: FTM Top Surgery by Dr. Lebowitz
YouTube Video: Transgender & Non-binary Keyhole Incision Top Surgery by Dr. Scott Mosser