17311

Mohs Micrographic Surgery, Head, Neck, Hands, Feet, Genitalia; First Stage

CPT 17311 describes the first stage of Mohs micrographic surgery (MMS), a specialized and highly precise technique for the removal of skin cancer. This specific code is designated for procedures performed on the head, neck, hands, feet, genitalia, or any anatomical location where the surgery directly involves deep structures such as muscle, cartilage, bone, tendon, major nerves, or large vessels. The defining characteristic of Mohs surgery is that the physician serves as both the surgeon and the pathologist. The procedure begins with the clinical identification of the tumor margins and the administration of local anesthesia. The surgeon typically performs a debulking of the visible tumor, followed by the excision of the first 'stage'—a thin layer of tissue encompassing the entire surgical margin. This tissue is meticulously mapped, oriented, and color-coded with surgical dyes to ensure that the exact location of any remaining cancer cells can be identified. The surgeon then supervises or performs the technical histopathologic preparation, including freezing, sectioning, and staining the tissue (usually with hematoxylin and eosin or toluidine blue). The surgeon then personally examines 100% of the peripheral and deep margins under a microscope. This comprehensive microscopic examination allows for the identification of 'roots' or 'silent' extensions of the tumor that might be missed in traditional wide local excisions. Code 17311 includes the removal of the tissue, mapping, and the microscopic examination of up to five specimens in the first stage. If the margins are clear after this stage, the procedure is complete; if not, additional stages are reported using add-on codes.

Clinical Indications

  • Basal cell carcinoma (BCC) in high-risk anatomic areas (e.g., central face, ears, eyelids)
  • Squamous cell carcinoma (SCC) in high-risk anatomic areas or with aggressive features
  • Tumors with poorly defined clinical borders
  • Recurrent skin malignancies following previous treatment
  • Malignancies in cosmetically sensitive areas where tissue sparing is critical
  • Aggressive histologic subtypes (e.g., morpheaform, infiltrating, or micronodular BCC)
  • Dermatofibrosarcoma protuberans (DFSP)
  • Melanoma in situ (lentigo maligna type) in specific anatomical locations
  • Large tumors (greater than 2cm) in areas with lower risk but requiring tissue preservation

Procedure Steps

  1. Identify and mark the clinical margins of the tumor and obtain informed consent.
  2. Administer local anesthesia to the surgical site.
  3. Perform debulking (curettage) of the gross tumor to define the extent of the lesion.
  4. Excise the first stage of tissue in a saucer-like shape to include peripheral and deep margins.
  5. Divide the excised tissue into specimens as needed for processing (up to 5 for 17311).
  6. Create a precise Mohs map correlating the excised tissue specimens to the surgical wound.
  7. Apply colored dyes to the tissue specimens to maintain orientation (mapping).
  8. Process the specimens using frozen section technique, including mounting, sectioning, and staining.
  9. The Mohs surgeon examines the slides under a microscope to evaluate 100% of the margins.
  10. If malignancy persists at the margins, the location is marked on the map for the next stage.

Coding Guidelines

  • Code 17311 is site-specific: it applies to the head, neck, hands, feet, genitalia, or any site involving deep structures (bone, muscle, etc.).
  • The Mohs surgeon must act as both surgeon and pathologist; if the pathology is referred to another physician, Mohs codes cannot be used.
  • 17311 represents the first stage. Subsequent stages at the same session are reported with 17312.
  • Up to 5 specimens are included in 17311. If a sixth or subsequent specimen is required in the first stage, use add-on code 17315.
  • Routine stains (H&E, Toluidine blue) are included. Special stains (e.g., IHC) may be reported separately using 88341 or 88342.
  • The repair of the surgical wound (e.g., 12031-15738) is not included in 17311 and should be reported separately.
  • If the Mohs procedure is performed on the trunk, arms, or legs (and does not involve deep structures), use 17313 for the first stage.

Associated ICD-10 Codes