Mohs micrographic surgery

Mohs micrographic surgery is a surgical procedure used to treat skin cancer. The goal of this procedure is to yield higher clearance rates by excising the tissue in multiple stages thereby preserving the healthier tissue as much as possible.

Mohs surgery is usually performed as a single day procedure under local anesthesia. It requires a single physician to perform the dual role as surgeon and pathologist. The act of physician’s dual role is very important to select the appropriate Mohs surgery code sets 17311-17315. If you know the process involved in Mohs surgery, then it is easier for you to assign the appropriate codes. Below is the steps involved in Mohs surgery and lets have a look onto it.

Steps involved in Mohs surgery:

STEP: 1 Examination and prep:

The very first step is to outline the visible tumor plus a small margin using a skin marker. The surgeon examines the visible tumor and plans what tissue to be removed during the surgery. The tumor site is then locally infused with anesthesia to completely numb the tissue. The surgery begins after this examination process.

STEP: 2 Removal of visible tumor (stage 1)

Once the skin has been completely numbed, the surgeon removes the visible portion of the tumor using careful surgical techniques.

STEP: 3 Sectioning, coloring and mapping:

The excised tissue sample is cut into smaller pieces or sections. Each section is numbered and color-coded with several dyes and makes reference marks on the skin to show the source of the sections. A map of the surgical site is then drawn to track exactly where each small portion of tissue originated.

STEP: 4 Tissue processing

This is the most time- consuming portion of the procedure. During the processing, the tissue is compressed and cut into extremely thin slices with a special device called cryostat. These slices are then placed on the microscopic slides and stained for further examination.

STEP: 5 Microscopic examination:

The surgeon can determine an additional stage only with the results of microscopic examination. Using a microscope, the surgeon examines all the edges and underside of the tissue on the slides for evidence of remaining cancer. If there is no evidence of cancer, the surgeon will proceed with the final step of surgical defect repair. If residual cancer is found, the Mohs surgeon utilizes the map to direct the removal of additional tissue (stage II).

STEP: 6 Additional stages:

If any section of the tissue demonstrates cancer cells at the margin, the surgeon returns to that specific area of the tumor, as indicated by the map, and removes another thin layer of tissue only from the precise area where cancer cells were detected. The newly excised tissue is again mapped, color-coded, processed and examined for additional cancer cells. The process is repeated to different stages (stage III, stage IV etc.) until the cancer is completely removed.

STEP: 7 Wound repair:

Once the site is clear of all cancer cells, the surgeon will focus on the wound repair. Sometimes the wound may be allowed to heal naturally or a skin graft or a flap can be employed for the purpose. It all depends on the size and location of the wound.

From the above steps, you can definitely understand how the Mohs surgery takes place and its significance in treating the malignancy. Now, let’s move onto the coding guidelines and the steps that you need to follow when coding Mohs surgery.

Checklist for the code selection:

  • Provider’s dual role ( surgeon and pathologist)
  • Number of lesions treated
  • Location of the procedure
  • Number of stages and blocks in each stage
  • Histopathology exams and biopsies other than the routine
  • Stains other than the routine
  • Surgical wound repairs.

Figure: Checklist for Mohs surgery codes:

1. Dual role as Surgeon and pathologist:

As a coder, you must use the Mohs surgery code sets (17311-17315) only when the physician plays the role of both the surgeon and pathologist. If either of these roles is delegated to another physician or qualified practitioner, then it is inappropriate to use the code sets 17311-17315.

2. Number of lesions treated:

If Mohs surgeon treats multiple lesions during the same session, then you need code for each lesion separately. For example, if the surgeon treats lesions on both neck and hand, then you need to report the below codes with appropriate modifiers:

For Neck – 17311

For hand – 17311 – 59

Modifier 59 is used to describe the service as “distinct procedural service”.

3. Location of the procedure:

CPT® categorizes Mohs micrographic surgery procedures by location, with one code set for head, neck, hands, feet, and genitalia, and a second code set for trunk, arms, and legs. Both anatomic categories include an add-on code for each additional stage after the first, with a stage defined as including up to five tissue blocks:

Anatomic regions: head neck, hands, feet, genitalia or any location with surgery directly involving muscle, cartilage, bone, tendon, major nerves or vessels

Primary code: 17311 – first stage, up to 5 tissue blocks

Add on code: +17312 – each additional stage after the first stage, up to 5 tissue blocks (list separately in addition to code for primary procedure)

Note: Report add-on code 17312 in addition to 17311, only.

Anatomic regions: Trunk, arms or legs

Primary code: 17313 – first stage, up to 5 tissue blocks

Add on code: +17314 – each additional stage after the first stage, up to 5 tissue blocks (list separately in addition to code for primary procedure)

Note: Report add-on code 17314 in addition to 17313, only.

Universal add-on code: +17315

There is an additional add-on code 17315 which can be reported in addition to any codes in the 17311-17314 range. This code typically represents “each additional block after the first 5 tissue blocks, any stage”.

4. Number of stages and blocks in each stage:

Most of the coders get confused with the terms stages and blocks and end up with a wrong code selection. Therefore it is essential to get clear with the terms when you step into the code assignment.

What is a stage?

An attempt to remove the tissue and processing for microscopic analysis to determine the evidence of cancer is called a stage. If the first stage shows positive margin, a second stage is followed and so on until the cancer is completely eradicated.

What is a block?

A tissue block is defined as an individual tissue piece embedded in a mounting medium for sectioning. A default of five tissue blocks is added to the code descriptions of 17311, 17312, 17313 and 17314. If any additional blocks after the first five blocks are performed, then add-on code 17315 is reported which is a universal add-on code as discussed earlier.

5. Histopathology exams and biopsies:

As Mohs surgery involves both the surgical and pathological component, histopathologic examination is included in the Mohs procedure and need not separately report the pathology codes 88302-88309. An exception to this rule exists when no prior pathology confirmation of a diagnosis is achieved. In such instances, you can report the diagnostic skin biopsy (11102, 11104, 11106) and frozen section pathology (88331) with modifier 59 to distinguish from the subsequent definitive surgical procedure of Mohs surgery.

6. Coding non-routine stains:

Mohs surgery includes “routine stains,” such as hematoxylin and eosin (H&E) or toluidine blue. However if the physician performs another special stains such as Oil Red O lipid stain which is not routine, then you can report 88314 in conjunction with 17311-17315 with modifier 59.

7. Surgical wound repairs

It is appropriate to bill separately the reconstruction codes for flaps or grafts performed to repair the wound resulted from Mohs surgery. However some insurers consider this repair as a cosmetic thereby resulting in claim denials. Therefore you need to link the cancer diagnosis code to the reconstruction code to prove the medical necessity.

Case Example:

The patient presents with three skin cancers: basal cell carcinoma of the right neck, squamous cell carcinoma of the right hand, and squamous cell carcinoma of the left ala. After prepping the patient and the sites, the physician first removes the BCC of the neck. He divides it into two tissue blocks. Under microscopic examination, the margins are negative. Next, the physician removes the SCC of the hand, dividing that stage into three tissue blocks. Under microscopic examination, the margins are negative. Lastly, the physician removes the SCC of the left ala, dividing the stage into six blocks. Under microscopic examination, there is a positive margin. The physician then takes a second stage, which is divided into two blocks. Under microscopic examination the margins are negative.

Code assignment:

Based on the checklist provided for the code selection, I have created a table to make it easier for coding the case.

Table: For coding Mohs surgery case:

Happy coding! Happy learning!


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