The Mohs surgical procedure is commonly used to excision basal and squamous cell carcinoma, particularly in the face, head, and neck areas. These are the areas of the body where cosmesis is an integral part of the surgical procedure. Also, if you look in the mirror, you can easily see that facial topography varies significantly from head to chin (pointy nose to sunken upper eyelid), and the skin thickness varies (cheeks have more fat, temples have less). Mohs considers these variations 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 techs may use slightly different techniques, but this protocol is a simple overview of this procedure. This outpatient procedure can be completed in an hour in a doctor's office.
Mohs Surgical Steps:
- The affected area is cleansed, marked, and numbed with local anesthetic.
- A saucer-shaped excision is made, and the stage one layer is removed.
- Notches are typically made in the excision and 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 entirely; 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 is revealed rather than a cross-section of the skin layers.
- Frozen sections are placed on a slide and stained with hematoxylin and eosin (H&E).
- The Mohs surgeon evaluates each slide; if the margins clear the tumor, the patient is ready for closure.
- If the tumor's margins are unclear, 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 to remove the affected area entirely until the margins are clear. It is not uncommon for an invasive tumor to be removed entirely after several stages.
