Mohs Micrographic Surgery Defined
What Is Mohs Micrographic Surgery?
Mohs micrographic surgery is named after its inventor, Dr. Frederic Mohs of the University of Wisconsin. It involves surgical excision of cancer containing tissue and systematic microscopic examination of all cut surfaces that are correlated with a drawn map of the wound (hence the term "micrographic"). It is a highly specialized procedure for the total removal of skin cancers.
How Is It Performed?

This method involves five separate steps: (1) removal of the bulk of the cancer with a skin scraper (a curette), (2) surgical removal of a thin underlying of tissue, (3) drawing a map and preparing stained frozen tissue sections, and (4) examination of the excised tissue under the microscope. After the tissue is removed, it is marked with two colored dyes to distinguish the two different skin edges. By doing this, we are able to pinpoint the exact location of any remaining tumor during the microscopic examination. If more cancer is found on the microscopic examination, its location is marked on the map (5), and the entire procedure (except step 1) is repeated, but only in the area of the remaining cancer. Only by careful, systematic microscopic examination of the removed skin can one be as certain as possible that no cancer remains.

How Does Mohs Micrographic Surgery Differ From Cancer Removal In The Operating Room With "Frozen Sections"?

During Mohs micrographic surgery, the tissue is examined in a different and more thorough manner than is normally performed by a pathologist associated with an operating room. Mohs micrographic surgery examines the entire sides and undersuface of the excised tissue. If one looks at a loaf of bread, Mohs micrographic surgery examines the whole crust rather than a few slices of the loaf.

Who Is Qualified To Perform Mohs Micrographic Surgery?
Physicians who are members of the American College of Mohs Micrographic Surgery have taken one year of training in Mohs micrographic surgery after a Dermatology Residency. According to CPT (Current Physician Terminology) billing rules used by all insurance companies, Mohs Micrographic Surgery "requries a single physician to act in two integrated, but separate and distinct capacities: surgeon and pathologist. If either of these responsibilites are delegated to another physician... these codes are not appropriate." Therefore, removal of skin cancer in the operating room and having the tissue examined by a pathologist is not Mohs micrographic surgery, and cannot be billed as such. By law (CLIA, 1988), only dermatologists and pathologists can interpret microscopic slides of skin.
© Richard G. Bennett, M.D. 2003