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  • Laboratory techniques dictate the quality of slides available for interpretation during MMS, and are therefore a critical step in ensuring high-quality patient care.

  • While the technologist is responsible for creating the slides that are read by the Mohs surgeon, given the high stakes, the ultimate responsibility for ensuring high-quality interpretable slides rest with the Mohs surgeon him- or herself.

image Beginner Pearls

  • Ideally, the MMS laboratory should have two cryostats so that in the event of failure, patients are not overly inconvenienced.

  • Several options are available for embedding tissue, including the heat-sink method, the glass-slide method, and the cryomold technique.

image Expert Pearls

  • Tissue freezing medium adheres better to dermis than to epidermis, so deep nicks or hatch marks help not only with orientation, but with tissue adherence to the slide as well.

  • Thin sections may be challenging to process, as they have a tendency to crumble or fall out of the embedding medium or rapidly flash-freeze prior to unrolling. Several approaches, including scoring with a warm scalpel blade and using cyanoacrylate glue, may be helpful.

image Don’t Forget!

  • Orienting relaxing incisions medial to the epidermal edge on a 20- to 45-degree angle may help allow the tissue to gently flatten out.

  • Charged, or so-called plus slides, may be helpful in encouraging tissue to adhere well to the slide.

image Pitfalls and Cautions

  • Slides should be wiped carefully; technicians who have trained with permanent section preparation may not be familiar with the rapidity with which Mohs surgeons begin to read slides.

  • Formation of an opaque film over the slide may result from the use of incompatible clearing agents and coverslipping media.

  • Most staining issues can be addressed by using compatible chemicals and by sufficiently blotting the slides and rack between reagents in order to avoid dilution and neutralization.

image Patient Education Points

  • Explaining to patients that all MMS laboratories are federally regulated may help bolster their confidence in the quality of an office-based laboratory.

  • The laboratory area should be centrally located for ease of access and clearly marked so that patients do not inadvertently attempt entry.

image Billing Pearls

  • When billing Medicare for MMS, the laboratory’s CLIA number must be attached to all claims.


High-quality histologic sections are the foundation on which Mohs micrographic surgery (MMS) is built. Indeed, the goal of complete margin control cannot possibly be attained if the Mohs surgeon is unable to effectively assess complete margins by reviewing crisp, clear, and complete histologic sections.

While much attention has historically been paid to MMS slide interpretation—and particularly post-MMS reconstruction—an appreciation of laboratory techniques for MMS slide preparation is of vital importance. In general, the technologist is responsible for creating the slides that are read by the Mohs surgeon, but given the ...

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