WILLIAMSBURG, VA. Consistent application of tissue nicks and annotated tissue transfer cards can significantly reduce the chance of error in Mohs surgery.
"Recurrence after Mohs surgery is very low, only 1%-2% at most, but when we look at the reasons behind those recurrences, 75% are due to human error, and of these, 10% are due to incorrect mapping and excision," said Dr. Tri H. Nguyen, director of Mohs micrographic and dermatologic surgery at the University of Texas M.D. Anderson Cancer Center, Houston.
"This includes tissue-orientation mistakes, mapping inaccuracies, mislabeling of sections or slides, and insufficient resection," Dr. Nguyen said at a meeting of the American Society for Mohs Surgery.
He methodically employs a system of identification strategies that nearly eliminates the chance of orientation errors, but an informal survey of fellowship programs showed that few physicians may be using this same level of caution.
Dr. Nguyen asked his residents about orientation techniques taught in the 14 Mohs fellowship programs for which they applied. Only three programs used preprinted maps, and only one used preprinted tissue transfer cards. Only five programs used tissue nicks to orient the sample, and only two of those used double nicks to add an extra layer of security.
"There are tremendous variations in the way we practice mapping and orientation, and probably all are adequate for primary, low-risk, single-stage Mohs resections," he said. "We run into problems with high-risk tumors with multiple convolutions or convexities, and in surgeries with multiple stages and multiple sites."
Anatomical maps and transfer cards can help reduce these problems. The cards have preprinted maps with illustrations of anatomical areas, and they also absorb moisture from specimens, which decreases the chance that they will shift position or fall off during the transfer. Corresponding paper maps have the same information printed on them.
"We have preprinted maps and transfer cards for every conceivable [anatomical area] on the head and neck, and blank ones for drawing locations on the extremities," Dr. Nguyen said.
Strategic tissue nicking adds a second layer of security to the surgery. "The argument over tissue nicks is pointless. There is no doubt that a properly made nick of the patient and the excised tissue leaves an indelible mark to go back and orient your sample," he said.
Single nicks, however, aren't sufficient. "With a single, there is always a chance the tissue will get dropped or shifted and you will lose the accuracy of your orientation. If you have a second nick consistently placed, you will always know exactly how the tissue is oriented. Two nicks ensure specimen orientation with or without" an anatomical transfer card, Dr. Nguyen said.
In double nicking, there should be a little space between the incisions. "If you place the second nick close to the peripheral edge, you are prone to tissue folding, which can mask tumor," he said.