Prior to initial incision, the site is marked with a surgical pen and given 1-mm margins around the clinically visualized lesion. The site is then cleansed with an antiseptic, typically a chlorhexidine solution. Local anesthesia is employed, most commonly with a 1:100,000 lidocaine and epinephrine injection. Marking of the tumor prior to numbing is imperative, as the boundaries of the tumor are typically obscured when the local cutaneous vasculature constricts and causes visualized blanching of adjacent skin. Many Mohs surgeons perform a brief curettage of the lesion with a nondisposable, dull curette to better define the tumor edges and to debulk any obvious exophytic tumor noted by the naked eye.
Prior to the first incision, the surgical site is scored in a variety of ways in order to properly orient the tissue after it has been removed from the patient. Mohs surgeons have differing opinions on how to score and/or mark the tissue, but a common practice is to make a nick at the 12 o’clock position. Following removal of the first stage, the nick will be visible on both the extirpated tissue and the tissue just above the surgical defect. This prevents potential confusion regarding orientation during tissue processing.
The majority of all WLEs are performed utilizing the scalpel blade at an angle 90° perpendicular to the plane of the skin. In MMS, a signature 45° angle with the tip of the scalpel pointing toward, and the handle pointing away from, the lesion is commonly used in order to bevel the tissue being excised (FIGURE 2). Once the tissue is excised, hemostasis is obtained using electrodessication/electrofulguration or electrocoagulation.
Tissue processing and microscopic evaluation
The technique of beveling allows the epidermis, dermis, and subcutaneous tissue to lie flat on the tissue block, so the Mohs surgeon can evaluate 100% of the excised tissue’s margins. The tissue is transported to a nearby lab for staining and processing. Even if near-perfect beveling is achieved, many stages will require bisecting, quadrissecting, or relaxing cuts in order to allow the margins to lie flat on the tissue block.
Using the scoring system made prior to incision, the tissue is oriented and stained with colored ink. Subsequently, a map is made with sections highlighting the colors used to stain designated areas of the tissue. This step is imperative for orientation during microscopic evaluation. Additionally, the map serves as a guide and log, should a section of the specimen have an involved margin and require another stage.
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