Noninvasive surgery is a term that is applied loosely depending on the source. Strictly speaking, a noninvasive surgery or procedure is one in which the skin is not broken in any way, either by cutting with a scalpel or injecting with a needle. Thus is the term noninvasive surgery is almost an oxymoron. While there are a few noninvasive surgical procedures, most surgeries that are called noninvasive are more accurately known as minimally invasive because a small incision or injection is required.
A true form of noninvasive surgery is a surgery that uses sounds waves, radiation, or non-penetrating light energy to perform some procedure. One example of noninvasive surgery is shockwave lithotripsy for the treatment of kidney stones. A probe is placed near the kidney and sound waves bombard the kidney stone causing it to break up into smaller pieces. The skin is not disturbed in this procedure and is thus noninvasive surgery.
Another example is radiation therapy or gamma knife therapy for the treatment of cancer. Beams of radiation are focused on tumor cells which destroy them, almost as if the beams were cutting out the tumor. The skin is unaffected but other tissues around the tumor could be injured during treatment.
Sometimes laser treatment of the skin or eyes could be considered noninvasive surgery. Laser procedures that do not disrupt the outer layers of skin or cornea but achieve some sort of surgical benefit would meet this definition.
The most common situations in which the term noninvasive surgery is inappropriately applied are in noninvasive heart surgery, noninvasive back surgery, and noninvasive spine surgery. One noninvasive back surgery (and perhaps the only one) is a procedure in which either sound waves or electrical currents are used to stimulate muscles and/or nerves in the back in the treatment of chronic lower back pain. This energy does not break the skin but it does seem to relax the muscles and desensitize nerve endings and nerves.
When the term noninvasive surgery is applied to other forms of back and spine surgery, it usually refers to minimally invasive surgery. For example, some vertebral fractures can be treated by simply injected a needle into the infected area, inflating a balloon to raise the spinal bone to its normal height, and then using the needle to inject a hard substance to take the place of the broken vertebra. While this procedure has completely eliminated the need for spine surgery in many patients, since there is a needle injection it is not strictly noninvasive spine surgery (but it is very close).
The same term has been applied to intra-arterial and intravenous procedures done on the heart, usually incorrectly. Coronary angioplasty, heart valve repair, and septal defect repairs can now be performed using a thin tube that is advanced through an artery or a vein in the leg to the heart. Because these procedures have eliminated the need for surgery in many cases, some have called them noninvasive heart surgery. Again, strictly speaking, this is incorrect because the skin in the leg needs to be cut in order to gain access to the blood vessel. Compared to open-heart surgery, though, these procedures are almost completely noninvasive.