What is Mohs Surgery?

In the early 1940s, Frederick Mohs, professor of surgery at the University of Wisconsin, developed a form of treatment for skin cancers he called chemosurgery.

“Chemosurgery” is derived from the words “chemical” and “surgery.” The addition of “Mohs” honors the doctor who developed the technique. It is a highly specialized form of treatment for the total removal of skin cancers. It is performed by a team of medical personnel that includes physicians, technicians, and nurses or medical assistants.

Dr. Mehrany, who is heading the team, is board certified in Micrographic Dermatologic Surgery after having had subspecialty fellowship surgical training in Mohs micrographic & reconstructive surgery techniques. A technician, whom you may not even meet, performs the important task of preparing the tissue slides, which are examined under a microscope by Dr. Mehrany.

The word “chemosurgery,” when used today, is really a misnomer. When Dr. Mohs initially introduced the procedures, he applied a chemical (zinc chloride) to the tumor and surrounding skin, which fixed the tissue prior to its removal. Since 1974, the procedure has been refined and improved upon, so the vast majority of cases are done using fresh tissue (omitting the chemical paste).

Although the official name for the procedure is Mohs micrographic surgery, we prefer the shortened version of Mohs Surgery. The surgery is performed as follows: the skin suspicious for cancer is treated with a local anesthetic, so there is no feeling of pain in the area. To remove most of the visible skin cancer, the tumor is scraped using a sharp instrument called a curette. A thin piece of tissue is then removed surgically around the scraped skin and carefully divided into pieces that will fit on a microscope slide; the edges are marked with colored dyes; a precise map or diagram of the tissue removed is made; and the tissue is frozen by the technician. Thin slices can then be made from the frozen tissue and examined by the doctor under the microscope.

Most bleeding is controlled using light cautery, although occasionally, a small blood vessel is encountered, which must be tied off with suture. A pressure dressing is then applied, and the patient is asked to wait while the slides are being processed. Dr. Mehrany will then examine the slides under the microscope to determine if any cancer is still present and subsequently annotate his map of the cancer location accordingly. If cancer cells remain, they can then be located at the surgical site on the patient by referring to the map. Another layer of tissue is then removed, and the procedure is repeated until Dr. Mehrany is satisfied that the entire base and sides of the wound have no cancer cells remaining. As well as ensuring total removal of cancer, this process preserves as much normal, healthy surrounding skin as possible.

The removal and processing of each layer of tissue take approximately 1-3 hours. Only 20 to 30 minutes of that is spent in the actual surgical procedure. The remaining time is required for slide preparation and interpretation. It usually takes the removal of two or three layers of tissue (also called stages) to complete the surgery. Therefore, by beginning early in the morning, Mohs surgery is typically finished in one day.  At the end of Mohs surgery, you will be left with a surgical wound free of tumor which is then reconstructed that same day.  Several options for reconstruction may be discussed with you in order to weigh your preference of what will provide the best possible cosmetic outcome versus what will provide the easiest and simplest recovery.