17313
Mohs Micrographic Surgery, Trunk, Arms, or Legs, First Stage
CPT 17313 describes the first stage of Mohs micrographic surgery performed on the trunk, arms, or legs. Mohs surgery is a highly specialized, tissue-sparing surgical technique used primarily for the treatment of skin cancers. The fundamental principle of this procedure is that the operating surgeon serves as both the surgeon and the pathologist. The process begins with the removal of the clinically visible tumor (often after a debulking excision). The surgeon then removes a thin layer of tissue—the first stage—which includes the entire deep and peripheral margins. This tissue is mapped and oriented precisely to the patient's wound. The specimen is then divided into blocks (up to five for code 17313), frozen, and sliced into extremely thin horizontal sections. These sections are stained, typically with Hematoxylin and Eosin (H&E), and examined under a microscope by the Mohs surgeon. If the surgeon identifies any malignant cells at the margins, the location is noted on the Mohs map, and a subsequent stage (CPT 17314) is performed at that specific site. This iterative process continues until all margins are clear. CPT 17313 is specific to the first stage in the anatomical regions of the trunk, arms, and legs. If the procedure requires more than five blocks in this first stage, add-on code 17315 is used. The procedure is preferred for tumors with aggressive histology, ill-defined clinical borders, or those that have recurred after previous treatment, as it offers the highest cure rate while preserving the maximum amount of healthy surrounding tissue.
Clinical Indications
- Basal cell carcinoma (BCC) on the trunk or extremities with aggressive histological features
- Squamous cell carcinoma (SCC) on the trunk or extremities greater than 2cm
- Recurrent skin cancer in any trunk or extremity location
- Tumors with poorly defined clinical borders
- Skin cancer arising in areas of prior radiation therapy
- Malignancies in immunosuppressed patients
- Microcystic adnexal carcinoma
- Dermatofibrosarcoma protuberans (DFSP)
Procedure Steps
- Preparation of the surgical site and administration of local anesthesia.
- Debulking of the gross tumor using a curette or scalpel.
- Excision of the first tissue stage (a thin layer) using a beveled incision to include peripheral and deep margins.
- Hemostasis of the surgical wound via electrocautery or pressure.
- Mapping and color-coding of the excised tissue to maintain orientation relative to the wound.
- Processing of the tissue in a cryostat to create frozen sections.
- Staining of the tissue sections (typically H&E or Toluidine Blue).
- Microscopic examination of the slides by the Mohs surgeon to assess all margins for malignancy.
- Documentation of the number of blocks and the presence or absence of residual tumor.
Coding Guidelines
- Code 17313 represents the first stage and includes up to 5 tissue blocks.
- This code is only used for the trunk, arms, and legs. For the head, neck, hands, feet, and genitalia, use 17311.
- The Mohs surgeon must act as both surgeon and pathologist; if the tissue is sent to an outside pathologist, Mohs codes cannot be reported.
- Report 17314 for each subsequent stage (Stage 2, Stage 3, etc.) on the trunk, arms, or legs.
- Use add-on code 17315 for each additional block beyond the initial 5 blocks in any stage.
- Surgical repair of the wound (e.g., 120xx, 131xx, 14xxx, 15xxx) is reported separately from the Mohs procedure.
- Routine biopsy of the site on the same day as Mohs is generally considered bundled unless it is a diagnostic biopsy for a new lesion, which may require modifier 59.