Moh's Surgery

Definition

Moh's surgery, also called Moh's micrographic surgery, is a precise surgical technique that is used to remove all parts of cancerous skin tumors while preserving as much healthy tissue as possible.

Purpose

Moh's surgery is used to treat skin cancers such as basal cell carcinoma, squamous cell carcinoma of the skin, melanoma, Bowen's disease, extramammary Paget's disease, leiomyosarcoma, laryngeal cancer, malignant fibrous histiocytoma, and Merkel cell carcinoma.

Malignant skin tumors may exist as strange, unsym-metrical shapes. The tumor may have long finger-like projections that extend across the skin (laterally) or down into the skin. Because these extensions may be composed of only a few cells, they cannot be seen or felt. Standard surgical removal (excision) may miss these cancerous cells leading to recurrence of the tumor. To assure removal of all cancerous tissue, a large piece of skin needs to be removed. This causes a cosmetically unacceptable result, especially if the cancer is located on the face. Moh's surgery enables the surgeon to precisely excise the entire tumor without removing excessive amounts of the surrounding healthy tissue.

Precautions

To reduce the risk of bleeding, the use of nonsteroidal anti-inflammatory drugs, alcohol, vitamin E, and fish oil tablets should be avoided prior to the procedure. Patients who use the anticoagulants aspirin, coumadin, or heparin, should consult with the prescribing physician before changing their use of these drugs.

Description

There are two types of Moh's surgery: fresh-tissue technique and fixed-tissue technique. Seventy-two percent of surgeons who perform Moh's surgery use only the fresh-tissue technique. The remaining surgeons use both techniques; however, the fixed-tissue technique is used in fewer than 5% of the patients. The main difference between the two techniques has to do with the preparation steps.

Fresh-tissue technique

Fresh-tissue Moh's surgery is performed under local anesthesia for tumors of the skin. The area to be excised is cleaned with a disinfectant solution and a sterile drape is placed over the site. The surgeon may outline the tumor using a surgical marking pen or a dye. A local anesthetic (lidocaine plus epinephrine) is injected into the area. Once the local anesthetic has taken effect, the main portion of the tumor is excised (debulked) using a spoon-shaped tool (curette). To define the area to be excised and allow for accurate mapping of the tumor, the surgeon makes identifying marks around the wound. These marks may be made with stitches, staples, fine cuts with a scalpel, or temporary tattoos. One layer of tissue is carefully excised (first Moh's excision), cut into smaller sections, and taken to the laboratory for analysis.

If cancerous cells are found in any of the tissue sections, a second layer of tissue is removed (second Moh's excision). Because only the section (s) that have cancerous cells are removed, healthy tissue can be spared. The entire procedure, including surgical repair of the wound, is performed in one day. Surgical repair may be performed by the Moh's surgeon, a plastic surgeon, or other specialist. In certain cases, wounds may be allowed to heal naturally.

Fixed-tissue technique

With fixed-tissue Moh's surgery, the tumor is debulked as described above. Trichloracetic acid is applied to the wound (to control bleeding) followed by a preservative (fixative) called zinc chloride. The wound is dressed and the tissue is allowed to fix for 6 to 24 hours, depending on the depth of the tissue involved. This fixation period is painful. The first Moh's excision is performed as above, however, anesthesia is not required because the tissue is dead. If cancerous cells are found, fixative is applied to the affected area for an additional 6 to 24 hours. Excisions are performed in this sequential process until all cancerous tissue is removed. Surgical repair of the wound may be performed once all fixed tissue has sloughed off, usually a few days after the last excision.

Preparation

Under certain conditions, such as the location of the skin tumor or health status of the patient, antibiotics may be taken prior to the procedure (prophylactic antibiotic treatment). Patients are encouraged to eat prior to surgery and bring along snacks in case of a lengthy procedure.

Aftercare

Patients should expect to receive specific wound care instructions from their physician or surgeon, but generally, wounds that have been repaired with absorbable stitches or skin grafts are kept covered with a bandage for one week. Wounds that were repaired using nonabsorbable stitches are covered with a bandage, which should be replaced daily until the stitches are removed one to two weeks later. Patients with nonabsorbable stitches may shower. Signs of infection (e.g., redness, pain, drainage) should be reported to the physician immediately.

Risks

Using the fresh-tissue technique on a large tumor requires large amounts of local anesthetic, which can be toxic. Complications of Moh's surgery include infection, bleeding, scarring, and nerve damage.

Normal results

Moh's surgery provides high cure rates for malignant skin tumors. For instance, the five-year cure rate for basal cell carcinoma treated by Moh's surgery is greater than 99%. The frequency of recurrence is much lower with Moh's surgery (less than 1%) than with conventional surgical excision.

Abnormal results

Tumors spread in unpredictable patterns. Sometimes a seemingly small tumor is found to be quite large and widespread, resulting in a much larger excision than was anticipated. Technical errors, such as those involving processing and interpretation of the tissue sections, may lead to local recurrence of cancer.

Resources

BOOKS

Gross, Kenneth, Howard Steinman, and Ronald Rapini, eds. Mohs Surgery: Fundamentals and Techniques. St. Louis, MO: Mosby, 1999.

PERIODICALS

Anthony, Margaret. "Surgical Treatment of Nonmelanoma Skin Cancer." AORN Journal (March 2000): 552-64.

Schriner, David, Danny McCoy, David Goldberg, and Richard Wagner. "Mohs Micrographic Surgery." Journal of the American Academy of Dermatology (July 1998): 79-97.

Belinda Rowland, Ph.D.

QUESTIONS TO ASK THE DOCTOR

• How long have you been performing Moh's surgery?
• Will you use the fresh-tissue or fixed-tissue technique?
• Will I have to alter the use of my current medications for this procedure?
• What will you do if you don't find the border of the cancerous lesion?
• How will the wound be repaired?
• Will I need a plastic surgeon to repair the wound?
• What is the cure rate for this type of cancer when treated by Moh's surgery?
• What is the chance that the tumor will recur?
• How often will I have follow-up appointments?

Fixative

—A chemical that preserves tissue without destroying or altering the structure of the cells.

Fixed

—A term used to describe chemically preserved tissue. Fixed tissue is dead so it does not bleed or sense pain.

Moh's excision

—Referring to the excision of one layer of tissue during Moh's surgery. Also called stage.