How is Mohs micrographic surgery performed today?

Mohs surgery is performed in the outpatient setting. Patients are instructed to plan for the procedure to last an entire day. After informed consent is obtained, the tumor site is identified, measured, and photographed. Local anesthetic is then infiltrated into the tumor. Prior to taking the Mohs layer, many surgeons will debulk the cancer with curette or scalpel to better delineate its dimensions. A saucer-shaped piece of tissue is then excised from the cancerous area by beveling the surgical blade at about a 45-degree angle (in contrast to traditional surgical techniques, where the incision is made perpendicular to the skin).

The specimen is then sectioned into manageable pieces, if needed, and these slices are color coded with ink. Using an anatomic cartoon representation of the site, a map is drawn to precisely label the area from which the tumor is taken. The tissue is then submitted to the Mohs histotechnician, who prepares frozen tissue sections under the supervision of the Mohs surgeon. These sections are obtained by cutting the undersurface in a horizontal plane so that the depth and most peripheral skin edge will be available for microscopic examination. Theoretically, 100% of the margin is examined, in contrast to routine histologic processes. If tumor is identified, the map is used as a guide to obtain additional tissue layers only from the areas of positivity until a tumor-free plane is reached. Between stages of Mohs surgery, the wound is covered with a temporary dressing, and the patients wait in a comfortable area. Various steps of the procedure are illustrated in Fig. 53-1 using an apple model.

Davis DA, Pellowski DM, Hanke WC: Preparation of frozen sections, Dermatol Surg 30:1479–1485, 2004.