SAN DIEGO Mohs surgery requires meticulous mapping.
A Mohs map preserves the integrity between the surgical wound and the histologic findings on the slides, Dr. Howard Steinman said at a meeting sponsored by the American Society for Mohs Surgery.
An accurate, readable Mohs map must show the wound shape and the location of reference marks for correct orientation. It also must depict the location of tumor and other findings in the surgical area, such as scars, unrelated tumors, and incomplete margins, he said.
The map is essential for avoiding orientation errors and serves as a pictorial representation of the pathology report. It is also a medicolegal document, and surgeons can and will rely on it to help remember what they did in any given case. The map is critical for communication with lab technicians and consulting physicians, and it serves as part of the operative report. As such, it is vital in the event of a lawsuit.
"The map is the only pathology report you have," said Dr. Steinman, a dermatologist in private practice in Chula Vista, Calif. "A good map will tell you what you did for a particular patient when you look at it years later."
In addition to tumor foci, the map must document incomplete surgical margins. "You want to be able to mark that there was an incomplete skin edge, to document why you needed to take another layer of tissue," Dr. Steinman pointed out.
Although mapping using digital photography is likely the wave of the future, it's worth developing a strategy for creating a functional Mohs map using other methods. Some surgeons use preprinted anatomic diagrams, whereas others use hand-drawn sketches or nondigital photographs. A representational shape of the wound is okay; it doesn't have to be precise. The map should be drawn larger than the actual size of the wound, however, so it will be easier to correlate findings between the microscope slides and the surgical wound, he said.
Before any tissue is processed, the Mohs map must include patient information, clinical information, the exact location of reference marks, and the wound shape. During tissue processing, the map depicts specimen subdivision patterns, tissue section-numbering schemes, and tissue inking patterns.
During the procedure, the Mohs map is essential for documenting the surgery, processing tissue, and maintaining orientation of the specimen and microscope slides to the wound. After the procedure, the map is an essential record of the work that was performed. When marking findings, most surgeons mark tumor foci in red and other findings in black on the map.
Tissue inking must be accurately drawn on the map and must appear the same both through the microscope and on the map. Inking orients and differentiates tissue specimens, and must be visible on the processed tissue wafers. Dr. Steinman recommends using a consistent drawing symbol for each color. "Pick one set of symbols and be consistent; use it for the rest of your career," he said. When subdividing large specimens, ink opposing cut edges the same color.
"I ink my specimens first and then mark the map, because if I mark the map first and do not ink the tissue accordingly, I have to go back and change the map," he said. Although Dr. Mohs used red as a tissue ink, many surgeons today favor blue, black, or green, because they are easier to see on the microscope slides.
Dr. Steinman tries to process the least number of tissue sections for each Mohs stage, processing specimens as one piece when possible. A consistent inking pattern should be developed for small, circular-shaped specimens, the most common first-stage specimen shape. Dr. Steinman uses blue ink from the 9:0012:00 reference marks and black ink from 12:003:00. He places a green dot at the 6:00 mark on a specimen. Another method is to simply place ink into the four reference nicks of the specimen. "The important thing is to pick a method and be consistent," he said.
In addition, making a "Pac Man" incision to subdivide a specimen can offer an internal orientation. "When you cut a surgical specimen in half or quarters and use only two ink colors along their cut edges, you have created identically shaped pieces. You then need to place a third color on only one of each pair," Dr. Steinman said. "The third color is vital to preserve orientation."
Be aware of dense inflammation, which often masks tumor. "If you see dense inflammation on your first or second tissue wafers, tumor may be present in the wound base that requires another stage of Mohs surgery," Dr. Steinman said. Respect the dense inflammation and mark it on the Mohs map.