microsurgery

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Surgery on minute body structures or cells performed with the aid of a microscope and other specialized instruments, such as a micromanipulator.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Relating to techniques of surgery on very small or delicate parts of the body.
• noun Surgical procedures that are very small.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun surgery using operating microscopes and miniaturized precision instruments to perform intricate procedures on very small structures