Mohs objective: Examine entire margin

April 1, 2006

Squared off re-excisions allow the possibility for part of the margin to be left unexamined.

"A Mohs second stage must include the area where the tumor was present at the end of stage I, be connected to the epidermis or to the defect, and the surgical margin of this specimen must be examined in its entirety," Dr. Tiefenbrunn tells Dermatology Times.

Speaking here at the 64th Annual Meeting of the American Academy of Dermatology, Dr. Tiefenbrunn shows results from an American Society for Mohs Surgery (ASMS) peer review. In addition to the criteria of adequate skin edge, deep margin and stain, cases are evaluated for adequacy of re-excision. To determine this, reviewers look at the size of the specimen, whether it has skin edge or ink around the entire specimen and whether the levels of tissue (such as infundibulae, sebaceous glands or fat) that are seen at the edges of the specimen are consistent with an adequate re-excision.

Unspoken enigma

When examining layers of an excised tumor, a valid Mohs case requires a complete exam in the plane of the skin surface and a series of planes aligned perpendicular to that skin surface, according to Dr. Tiefenbrunn, clinical instructor, Washington University, St. Louis.

"By looking at a two-dimensional section, we must reconstruct the location of our tumor in the defect in a three-dimensional way," Dr. Tiefenbrunn says. "In some cases, we only think that we have examined the entire margin and found it clear. Rather, we have failed to re-examine a positive portion or we have left areas that we have not examined at all."

Inappropriate inking may be the reason complete margins between stages I and II are missed, and this aspect of Mohs theory is the secret of Mohs surgery that is often not discussed, Dr. Tiefenbrunn says. In addition, by checking the levels of the tissue at the periphery, the dermatologist can determine if it is possible that not all of the tumor has been included in the re-excision.

"A complete second layer (excision) is mathematically the most sound," Dr. Tiefenbrunn says. "This is like setting a leaking ice cream bowl in a larger bowl. Smaller re-excisions are sometimes desirable; these must overlap the residual tumor, connect to the defect on the skin surface and at depth and present evidence that these connections have been examined."

Marking correct topography

Squared off re-excisions allow the possibility for part of the margin to be left unexamined.

The squared-off end of the specimen is hard to flatten onto the slide; when this type of excision is accompanied by ink of the skin edge instead of the free edge, tumor can be left behind, even though the sections are clear. Bevel cut specimens are much easier to flatten, explains Dr. Tiefenbrunn. Ink on the previously exposed surface of the free edge ensures examination of the line where stage II connects to the defect, which is the most likely place for tumor to remain.

When the tumor is in the dermis, a specimen with skin edge or with a higher level of dermis is needed. The deep tissue of the specimen also needs to contain a layer deep to the one containing the tumor.

"Correct inking ensures a complete exam and determines a connection with the previous defect," Dr. Tiefenbrunn says. "In addition to ink, however, one must consider which level of the skin the ink is on. If the well-connected excision starts below the level of the tumor, the bowl is still leaking."