Mohs Micrographic Surgery: Coding and Billing Explained

Mohs surgery, also known as chemosurgery, developed in 1938 by a general surgeon, Frederic E. Mohs, is microscopically controlled surgery used to treat common types of skin cancer. During the surgery, after each removal of tissue and while the patient waits, the tissue is examined for cancer cells.

A surgical procedure used to treat skin cancer. Individual layers of cancer tissue are removed and examined under a microscope one at a time until all cancer tissue has been removed. Also called Mohs surgery.

Mohs was rarely chosen for Melanoma surgery for fear that some microscopic melanoma cells might be missed and end up spreading around the body (metastasizing). However, efforts to improve the Mohs surgeon’s ability to identify melanoma cells have led to special stains that highlight these cells, making them much easier to see under the microscope. Thus, more Mohs surgeons are now using this procedure with certain melanomas.

Steps in Mohs Surgery

• Typically, Mohs surgery is performed as an outpatient procedure in the physician’s office. Although the patient is awake during the entire procedure, discomfort is usually minimal and no greater than it would be for more routine skin cancer surgeries.
• Tissue cut in saucer shape and  frozen on a cryostat, and technician removes very thin slices from the entire edge and undersurface. These slices are then placed on slides and stained for examination under the microscope. (This is the most time-consuming portion of the procedure, often requiring one hour or more to complete.
• The Mohs surgeon carefully examines the entire undersurface and complete edge of the specimen, and all microscopic “roots” of the cancer are precisely identified and pinpointed on the Mohs map.
• Upon microscopic examination, if residual cancer is found, the Mohs surgeon utilizes the Mohs map to direct the removal of additional tissue (Stage II).
• Note that additional tissue is removed only where cancer is present.
• This process is repeated as many times as necessary to locate any remaining cancerous areas within the tissue specimen (Stage III, Stage IV, etc.)
• When microscopic examination reveals that there is no remaining tumor, the surgical defect is ready for repair.

How do code Mohs Micrographic surgery (CPT 17311-17315)?

Coding of Mohs surgery can be done with three important thing:

• Location of treated lesion
• Number of Stage
• Required Blocks

There are some following steps for coding Mohs surgery:

In Mohs technique, most important thing is that pathologist and surgeon should be same. Mohs requires that a single physician act as both surgeon (excising tissue) and pathologist (immediately examining excised tissue to determine clear margins). If both are not same then never coded as Mohs.

The use of CPT codes 17311-17315 is reserved for the surgeon who removes the lesion and prepares and interprets the pathology slides. The surgical pathology codes 88300-88309 and 88331-88332 and 88342 are part of the Mohs surgery and are bundled into 17311-17315.

Identify location of lesion. According to location, choose appropriate code.

• For lesions of the head, neck, hands, feet, and genitalia, or any location with surgery directly involving muscle, cartilage, bone, tendon, major nerves, or vessels, use code 17311 and add-on code 17312.
• For lesions of the trunk, arms, and legs, select code 17313 and add-on code 17314.
• Regardless of location, might also need to report add-on code 17315.

Check number of Stage and Blocks.

Physician removes the cancerous or possible cancerous tissue in some stages

The first stage is to excise the lesion. The specimen is divided into smaller portions, called blocks.

“a tissue block … is defined as an individual tissue piece embedded in a mounting medium for sectioning.” The location of each block within the stage is carefully mapped, and each block is examined for cancer cells.

Each time the surgeon excises material counts as a stage. Each slide resulting from an individual stage counts as a block.

CPT code 17315 may be used to report each block after the first 5 blocks for any single stage (17315 is used as an add-on code to 17311, 17312, 17313 or 17314). Please note that this code refers to the number of blocks, not number of slides.

If the surgeon/pathologist uses the Mohs technique on multiple lesions during the same session, code for each lesion separately.

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 nose. After prepping the patient and the sites, the physician first removes the Basal Cell Carcinoma of the neck. He divides it into two tissue blocks. Under microscopic examination, the margins are negative. Next, the physician removes the Squamous Cell Carcinoma of the hand, dividing that stage into three tissue blocks. Under microscopic examination, the margins are negative. Lastly, the physician removes the Squamous Cell Carcinoma of the left nose, 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.The appropriate coding in this scenario is:

• 17311 (neck)
• 17311-59 Distinct procedural service (hand)
• 17311-59 (nose)
• 17312 (second stage of nose)
• 17315 (extra block of first stage of nose)

For each additional (separate) lesion treated with Mohs surgery on the same day, bill each first stage as a 17311 or 17313 as appropriate, on a separate claim line with a -59 modifier. Separately identify the additional stages for these lesions by billing the 17312 or 17314 on separate claim lines with a -59 modifier, and the appropriate units of service for these lesions.

Billing point : We should be focus

If Mohs on a single site cannot be completed on the same day because the patient could not tolerate further surgery and the additional stages were competed the following day, you must start with the primary code (CPT code 17311) on day two. Computer edits will reject claims where a secondary code (e.g., CPT code 17312) is billed without the primary code (e.g., CPT code 17311) also appearing on same date of service, same claim.

Report the -59 modifier on the same line as the biopsy procedure code and the pathology procedure codes: 11100, 11101, and 88331. Do not report modifier -59 on the same detail line as the Mohs surgical procedure.

Mohs surgery services are payable under Medicare Part B in the following places of service: office (11), inpatient hospital (21), outpatient hospital (22), ambulatory surgery center (24), independent clinic (49), federally qualified health center (50), state or local public health clinic (71) and rural health clinic (72).

Only physicians (MD/DO) may perform Mohs micrographic surgery.