Mohs Micrographic surgery is a highly effective procedure used in skin cancer treatment. There are indications that a tumor requires Mohs. These indications are when tumors occur in high risk areas such as around the eyes, ears, nose and lips. These areas have higher recurrence rates than those located in other areas of the body. Other indications are recurrent tumors, tumors measuring greater than 2cm in diameter and incompletely excised tumors. Those that do not meet these criteria but are indications for Mohs Micrographic surgery (regardless of their location) include cutaneous malignancies with ill-defined tumor borders and aggressive histology.
Mohs micrographic surgery is performed on an outpatient basis. A sterile prep and draping is performed on all patients. Then the clinically apparent borders of tumor are marked using 1 percent gentian violet. Lidocaine 1 percent with epinephrine 1:100,000 is injected using a 30gauge needle for local anesthesia. The tumor is then debulked with a scalpel or curette to help define the depth and peripheral involvement of the malignancy. Following the debulking procedure, 1 percent gentian violet is again used to mark a 2-mm margin of normal-appearing skin around the debulked area.
The area thus outlined is incised using a No. 15 scalpel blade at a 45-degree angle to the skin. Then the skin is scored with several hash marks to allow precise anatomical orientation of the layer to be removed. This layer, which is approximately 3 mm in thickness, is then dissected free, using an iris scissors or a scalpel blade. The layer is placed on a 4-inch x 4-inch gauze, keeping its exact anatomical orientation to the patient. Hemostasis is achieved using electrocoagulation. The wound is then covered with an antibiotic ointment, non-adhesive gauze, and a pressure dressing. In the meantime, the patient relaxes in the recovery room for 30 to 45 minutes while the tissue is being processed.
A map of the specimen is drawn to correspond exactly to the layer removed. The specimen is divided into small pieces, which wiII ensure that it can fit onto a glass slide. These pieces are color coded using red and blue dyes so that all sides of the specimen can easily be identified. These colors correspond to the markings placed on the map. The scored hash marks are also indicated on the map to preserve the exact anatomical orientation.
The tissue is then delivered to the histology technician, who embeds the tissue in such a way that the entire undersurface (deep margin) of each specimen as well as its peripheral epidermal edge can be seen in one horizontal view on the slide. These specimens are then reviewed by the Mohs surgeon, who marks any residual tumor, which is easily located by the colored dyes seen on each specimen.
The location of this residual tumor is marked on the schematic map, which is used to determine the site from which the next layer will be taken. The tissue removed in the following layer is only that tissue involved with tumor; normal areas of the specimen that do not contain tumor are left alone. The Mohs technique is considered a tissue- sparing technique because only tissue involved with tumor is removed, which maximally preserves normal tissues. Reconstruction of the defect can follow after all tumor is removed.
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