17312
Mohs Micrographic Surgery, Head, Neck, Hands, Feet, Genitalia; Each Additional Stage
CPT 17312 describes an add-on procedure performed during Mohs micrographic surgery, a specialized technique for treating high-risk skin cancers. This specific code is designated for the second and each subsequent stage of the Mohs procedure when the surgical site is located on the head, neck, hands, feet, genitalia, or any other anatomical site where the surgery directly involves deep structures such as muscle, cartilage, bone, tendon, major nerves, or vessels. The core of the Mohs technique is that the surgeon serves as both the surgeon and the pathologist. The procedure begins with the removal of the clinically visible tumor (the first stage, reported with code 17311), followed by the excision of thin horizontal layers of tissue. Each layer (or stage) is meticulously mapped, color-coded with specific dyes, and processed into frozen sections for immediate microscopic examination. The surgeon evaluates 100% of the peripheral and deep surgical margins. If the microscopic analysis reveals remaining cancerous cells, the surgeon proceeds to the next stage, which is where CPT 17312 is applied. This code represents the technical work of the subsequent excision, the mapping, and the professional interpretation of the slides. This iterative process continues sequentially until a clear margin is achieved. By integrating surgical removal with immediate microscopic pathology, Mohs surgery maximizes the preservation of healthy tissue and achieves the highest possible cure rate for malignancies like basal cell carcinoma and squamous cell carcinoma, particularly in areas where tissue conservation is functionally or aesthetically critical.
Clinical Indications
- Basal cell carcinoma in high-risk anatomic areas (H-zone of the face)
- Squamous cell carcinoma in high-risk or sensitive areas
- Dermatofibrosarcoma protuberans (DFSP)
- Recurrent skin malignancies
- Tumors with ill-defined clinical borders
- Tumors located on the head, neck, hands, feet, or genitalia
- Malignant lesions involving muscle, cartilage, or bone
Procedure Steps
- Administration of local anesthesia to the surgical site.
- Debulking of the gross tumor (if not already performed in the first stage).
- Surgical excision of a thin layer of tissue encompassing the entire wound bed.
- Creation of a detailed map of the excised tissue correlating it to the surgical site.
- Color-coding the specimen edges with surgical dyes to maintain orientation.
- Processing the tissue using a cryostat to create frozen section slides.
- Microscopic examination of the entire margin by the Mohs surgeon.
- Identification of any persistent tumor 'roots' on the map.
- Repetition of the process (additional stages) until the margins are tumor-free.
Coding Guidelines
- CPT 17312 is an add-on code and must be reported in conjunction with the primary code 17311.
- Code 17312 should be reported for the second, third, and any subsequent stages performed during the same operative session.
- The surgeon must perform both the surgical excision and the microscopic pathology interpretation; if a separate pathologist is used, Mohs codes are not applicable.
- Each unit of 17312 covers one stage including up to five tissue blocks. If more than five blocks are required for a single stage, use add-on code 17315.
- Surgical repair of the resulting wound (e.g., intermediate repair, complex repair, or flaps) is reported separately from the Mohs procedure.
- Do not report 17312 for stages performed on the trunk, arms, or legs unless they involve muscle, bone, or other deep structures defined in the code descriptor.