Mohs Micrographic Surgery

By Betty A. Johnson, CPC, CCS-P, CIC, CCP

Mohs codes are reported when the physician serves as both the surgeon and the pathologist.

Mohs micrographic surgery is a highly specialized procedure in which the physician acts as both pathologist and surgeon. Find out the reasons for performing the procedure and how to code the procedure.

Reasons for Mohs

Physicians perform Mohs to eradicate cancerous lesions on the skin. Skin cancer is the most common form of cancer in the United States, with more than a million new cases reported each year. One out of every three newly reported cancers is a skin cancer. Skin cancer can be found on any part of the body but is most often encountered (80 percent of the time) on the sun-exposed areas: the face, head or neck. The primary cause of skin cancer is ultraviolet radiation, most often from the sun, although it can be from artificial sources like sunlamps and tanning booths. The two most common forms of skin cancer are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC).

BCC is the most common form of skin cancer, with approximately 800,000 cases reported annually. It arises in the basal cells located in the epidermis, which is the outermost layer of skin. SCC is the second most common form of skin cancer, with approximately 200,000 cases reported annually. It is also found in the epidermis, but can metastasize (spread) to other areas if left untreated. Melanoma makes up the smallest percentage of skin cancers, but it is the most serious. It is also almost 100 percent curable if caught in the early stages. If not caught and treated, however, it can metastasize and be fatal. Mohs micrographic surgery may be a method of treatment for all of the above types of skin cancer.

The Procedure

Traditional skin cancer treatment generally involves excising the lesion and a reasonable margin, and sending that specimen for separate pathologic evaluation. If cancer cells still show at the margins, the patient returns to the clinic for a wider excision and the new specimen is then sent back to the pathologist for additional examination. The process is repeated until the margins show free of cancer cells, which results in multiple trips to the physician, multiple procedures performed and stress for the patient. Mohs micrographic surgery changed that tradition.

Dr. Frederic Mohs was a general surgeon who pioneered the excision of skin cancers under complete microscopic control in the 1930s. He developed a technique for excising thin layers of tissue, freezing them and examining them pathologically. The technique has been refined over the years and now is usually performed in one visit. Following are the basic steps to performing Mohs:

  1. The surgeon removes the visible cancer with a thin layer of additional tissue. This is stage one.
  2. The removed tissue is cut into sections (blocks), stained and marked on a detailed diagram, also called a Mohs map.
  3. The tissue is frozen on a cryostat, and very thin slices are removed from the entire edge and undersurface. The blocks are placed on slides and stained for examination under the microscope.
  4. The surgeon microscopically examines the slides completely, identifying and mapping the “roots” on the Mohs map. If no residual cancer is found, the procedure is ended.
  5. If residual cancer is found, the surgeon uses the map to pinpoint the removal of additional tissue. This is stage two. The procedure would be repeated as many times (stage three, stage four, etc.) with as many blocks as necessary until microscopically, no residual tumor remains.

Mohs has the highest cure rate (up to 99 percent) for SCCs and BCCs. A typical surgery takes between four and six hours. Mohs is indicated for skin cancers that have recurred following previous treatment, that are at high risk for recurrence, and/or skin cancers that occur in areas like the nose, eyelids, lips, hairline, hands, feet and genitals, where maximal preservation of healthy tissue is critical for cosmetic or functional purposes.

Coding Mohs

In CPT® 2007, the method for reporting Mohs changed. The codes are now differentiated by anatomic site to better distinguish the work involved in the various areas, and are further broken down by units of service, as follows:

17311 describes Mohs to the head, neck, hands, feet, genitalia, or any location with surgery directly involving muscle, cartilage, bone, tendon, major nerves or vessels; first stage up to five tissue blocks.

17312 is an add-on code to report each additional stage after the first stage, up to five tissue blocks.

17313 describes Mohs to the trunk, arms or legs; first stage up to five tissue blocks.

17314 is an add-on code to report each additional stage after the first stage, up to five tissue blocks.

17315 is an add-on code that describes each additional block after the first five tissue blocks, any stage at any anatomic location.

To report the service properly, the coding professional will need to know the number of stages and the number of blocks per stage. Consider the following example: A physician performs Mohs surgery on a patient with a basal cell carcinoma of the face. The physician takes the first stage with four tissue blocks, but does not remove all of the cancer. A second stage is removed with seven tissue blocks. The second stage comes back and shows that the physician completely excised the cancer. The correct way to code the scenario is:

17311 First stage up to five blocks to the face.

17312 Second stage up to five blocks.

17315 x 2 The additional two blocks in the second stage.

A final important fact to remember is that in order to code a Mohs procedure, the physician must act as both surgeon and pathologist. The new code descriptors fully state everything that must be performed, “…including removal of all gross tumor, surgical excision of tissue specimens, mapping, color coding of specimens, microscopic examination of specimens by the surgeon, and histopathologic preparation including routine stain(s) (e.g., hematoxylin and eosin, toluidine blue).”

Check out the new guidelines and descriptors in CPT® for further explanation.

Resources: CPT® 2007 Professional Edition, American Medical Association, American Cancer Society, American Academy of Dermatology, American Society for Mohs Surgery.

Betty A. Johnson, CPC, CCS-P, CIC, CCP, is the president and CEO of CPC Solutions Inc., a Chicago-based health care consulting firm. Ms. Johnson is also a former officer of the AAPC’s National Advisory Board.

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