Overview:
For decades, Mohs micrographic surgery
has proven effective in getting to the roots of skin cancer by
combining the surgical removal of cancer with the immediate microscopic
examination of the tumor and underlying diseased tissue. This
process allows dermatologists trained in Mohs surgery to see beyond
the visible disease and precisely identify and remove the entire
tumor. . .and nothing but the tumor.
PROCEDURE
Mohs micrographic surgery is performed on an outpatient basis.
Patients are assessed for their anxiety and are frequently given
a benzodiazepine sublingually approximately 15 minutes prior to
surgery. 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.
