The Mohs surgical procedure is commonly used for the excision of basal cell and squamous cell carcinoma, particularly in the areas of the face, head, and neck. These are the areas of the body where cosmesis is an important part of the surgical procedure. Also, if you look in the mirror, you can easily see that facial topography varies greatly from head to chin (pointy nose to sunken upper eyelid), and the skin thickness also varies (cheeks have more fat, temples have less). Mohs takes these variations into consideration and preserves the healthy tissue, while completely removing the affected skin. Mohs is performed on recurrent skin cancer, or a tumor that has ill-defined margins, as well as on skin with a critical/functional location.
The Mohs surgical procedure is outlined in the following steps. Mohs surgeons and Mohs techs may use techniques that differ slightly, but this protocol is a simple overview of this procedure. This is an outpatient procedure that can be completed in an hour in a doctor's office.
Mohs Surgical Steps:
- Affected area is cleansed, marked, and numbed with local anesthetic.
- Saucer-shaped excision is made, then stage one layer is removed.
- Notches are typically made in the excision as well as the surrounding skin to maintain orientation.
- The excised "pie" is inked and mapped to show corresponding margins and orientation.
- Small excisions can be frozen and cryosectioned in its entirety; if large, the "pie" is typically cut into four wedges and each wedge is frozen and cryosectioned separately.
- The "pie" is frozen epidermis down on the chuck, with the dermis/subcutis surface exposed entirely. This is the key to complete surgical margin evaluation.
- The entire "pie crust" is cryosectioned for complete margin evaluation. The cut surface, rather than a cross section of the skin layers, is revealed.
- Frozen sections are placed on a slide, then stained with hematoxylin and eosin (H&E).
- Each slide is evaluated by the Mohs surgeon and if the margins cleared the tumor, then the patient is ready for closure.
- If the margins are not clear of the tumor, the stage two excision is marked and removed ONLY in the area that still contains the cancer cells.
- Steps 6 through 9 are repeated as often as needed in order to remove the affected area completely until the margins are clear. It is not uncommon for an invasive tumor to be removed completely after several stages.