Mohs micrographic surgery

What is Mohs micrographic surgery?

Mohs micrographic surgery, or Mohs surgery, is a precise surgical technique in which excision fur Cancer is verified by microscopic margin control. It offers the highest healing rates while maximizing the preservation of healthy tissue. The principles behind this were developed by Dr. Frederic Mohs in the 1930s.

Mohs surgery is recognized as the treatment of choice for high risk basal cell carcinoma and scaly cellular carcinoma Skin cancer is progressively eliminated in stages. After each stage, the excision margins are examined microscopically for any remaining cancer cells, and this process is repeated until all of the cancer has been removed.

What is the difference between Mohs surgery and standard excision?

In standard excision, the tissue sample is sent for histological processing while the wound is closed. Processing takes several days during which cross sections (or vertical sections) are created at various distances through the sample and evaluated microscopically by a pathologist. The pathologist looks for skin cancer at the margins of each section, but these are only a fraction of the actual excision margin.

In Mohs surgery, histological processing is done on the day of surgery and the wound is only closed after it has been confirmed that all of the cancer has been removed. The cleavage margin is examined using an embedding technique that allows horizontal sections to be cut involving all deep and radial cleavage margins. If any tumor is visible on these sections, it means the excision is incomplete and the patient requires an additional Mohs stage.

A mapping process and color coding system is used during Mohs surgery to precisely locate any remaining cancer, and tissue is only removed if it contains cancer. This process preserves healthy tissue.

Mohs surgery results in higher clearance rates than standard excision and smaller wounds, thus better cosmetic results.

The steps involved in Mohs surgery

Mohs surgery is usually performed as a one-day procedure in a local setting. anesthesia. It involves the following steps:

1. The visible tumor plus a small margin is outlined with a skin marker and a reference map or grid is drawn on the patient (often with temporary sutures).
2. The area is excised at a 30 to 45 degree angle at the radial margins.
3. Haemostasis is obtained and the wound is temporarily clothed.
4. The excised tissue sample is divided into two or more sections that are color-coded using special tissue dyes.
5. A mapping process ensures that the residual tumor seen under the microscope can later be matched to the patient's exact location using a paper map or digital photographs and image processing software (see example).
6. A specialized histotechnician or biomedical scientist embeds and freezes the tissue in a cryostat to create horizontal sections of the entire excision margin.
7. The Mohs surgeon examines the microscopic sections for any remaining cancer.
8. Any remaining cancer is accurately drawn on the map or digital image.
9. This map or image is used to identify the area of the patient from which more tissue needs to be removed.
10. See step 2. The process is repeated until the patient is tumor free.
11. The wound is closed; see the topic on wound closure for an overview of techniques.

See clinical images of Mohs surgery…

What types of skin cancer are best treated with Mohs surgery?

Mohs surgery is widely accepted as the first-line treatment for high-risk basal cell carcinoma and squamous cell carcinoma. Although different criteria are used around the world, the main reason to perform Mohs is to minimize the risk of incomplete excision. This reduces the burden on the patient and can prevent a large and costly recovery.splits later.

Mohs surgery has the greatest benefit for a tumor at high risk of incomplete excision, such as:

• Recurrent or incompletely removed tumor
• Tumor arising on skin previously exposed to radiotherapy
• Large tumor, especially in the head and neck area
• Tumor that has ill-defined clinical borders
• Basal cell carcinoma with an aggressive growth pattern in histology (infiltrative, micronodular or with perineural invasion)
• Squamous cell carcinoma with increased risk of metastasis (eg, located in the ear, lip; with perineural invasion; or in an immunosuppressed patient)

Mohs may also be appropriate when a large reconstruction is needed to close the defect or when the tumor is in a cosmetically sensitive area.

In 2012, a joint effort by several medical organizations in the US led to the development of appropriate use criteria for Mohs surgery. These criteria can be used as a guide when considering Mohs surgery, although they may not apply in all jurisdictions [1].

Mohs for other types of skin cancer.

There is a lot of evidence that Mohs is the best form of surgery for high-risk basal cell carcinoma and squamous cell carcinoma. Large trials comparing Mohs with standard excision for other types of skin cancer are lacking.

In Mohs surgery, tumor cells must be accurately identified on microscopic examination of frozen sections. This can be a challenge in some types of skin cancer, such as:

• Atypical fibroxanthoma
• Very poorly differentiated squamous cell carcinoma
• Dermatofibrosarcoma protuberans
• Microcystic attached carcinoma
• Lentigo evil /melanoma in the place
• Extramammary Paget's disease

For these tumors, variations of Mohs surgery can be applied that follow the basic principles of Mohs surgery (microscopic margin control, horizontal embedding, and tissue mapping and color coding) but use paraffin-embedded sections instead of sections. frozen. This allows the use of immunohistochemical markers to help identify tumor cells.

Such techniques are sometimes collectively called slow Mohs. They include the 'Tuebingen Cake' and 'Muffin' [2] techniques.

How effective and cost-effective is Mohs surgery?

Mohs surgery results in fewer tumor recurrences than standard excision of basal cell carcinoma and squamous cell carcinoma. Reappearance Mohs rates are generally reported between 1 and 5%, depending on tumor type and length of follow-up.

In a randomized clinical trial with 10 years of follow-up, recurrence rates were:

• 4.4% for Mohs surgery and 12.2% for high-risk standard excision primary basal cell carcinoma
• 3.9% for Mohs and 13.5% for standard excision for high risk recurrent basal cell carcinoma [3].

Several studies have also found Mohs to be more cost-effective than standard excision. The main reason for this is that there are fewer expensive operations for recurrent tumors compared to standard excision [4-5].