Mohs slide preparation: Artifacts require troubleshooting algorithm

October 1, 2008

Artifacts in Mohs slide preparation typically stem from problems with microtome blades, microtome adjustments or cryostat temperatures, an expert says.

Key Points

Williamsburg, Va. - To maximize the accuracy and efficiency of Mohs micrographic surgery, technicians must know how to troubleshoot slide-preparation artifacts, according to a surgical pathologist with 30 years' experience performing Mohs surgery.

"The most important issue for Mohs technicians is to have an algorithm for troubleshooting, so they can look at an artifact, put it in a particular category and troubleshoot it themselves while they're working on a case," says John B. Campbell, M.D., a surgical pathologist with San Diego-based Pacific Pathology Inc.

Without such an algorithm, recurring problems can compromise a technician's ability to cut specimens and slow down everyone involved, he says.

Dr. Campbell says minor artifacts can stem either from surgical problems, such as cautery, sutures or blood pooling, or from staining issues.

"The staining and surgical artifacts are usually pretty obvious to the reviewer. The ones that are harder to diagnose are those that have to do with the microtome blades, cryostat temperatures or microtome adjustments," Dr. Campbell tells Dermatology Times.

Blade artifacts

Blade artifacts tend to be the most common type of slide-preparation artifact Mohs technicians will encounter, Dr. Campbell says.

Technicians must use sharp blades to cut tissue samples, he says, and these blades can either be disposable or permanent.

"Both types of blades have their own issues regarding sharpness. With disposable blades, sometimes technicians can get bad lots or bad quality blades," which Dr. Campbell likens to purchasing razor blades that don't last long.

Conversely, he says, permanent blades can't be sharpened on a variety of sharpeners.

"They need to be dedicated to one sharpener to get a perfect bevel and a very sharp edge. That's usually the biggest issue with permanent blades," Dr. Campbell says.

Other blade issues include problems stemming from sectioning for prolonged periods from one area on the blade. Instead, he advises using the entire face of the blade to produce uniform wear.

Dr. Campbell recommends that technicians keep a spare blade on hand so there's always a sharp one available.

If tissue appears shredded, especially the fat, the artifact is most likely temperature-related, Dr. Campbell says.

In this regard, "The cryostat should be capable of keeping the box temperature between minus 25 and minus 30° Centigrade with the door open," he adds.

Microtome adjustments

As for microtome adjustments, Dr. Campbell says that avoiding problems here requires adhering to a routine microtome maintenance schedule. This will keep equipment clean and well lubricated.

"Artifacts related to the microtome (the instrument inside the cryostat that actually slices the tissue) include compression lines, thick and thin sections or the 'Venetian blind' effect - the tissue looks like it has Venetian blinds across it," he says.

A simple troubleshooting algorithm involves asking oneself whether artifacts are present in a slide, and if so, which category they fall into, he says.

"If the artifact is definitely related to the blade," Dr. Campbell says, "then try a new spot on the blade or substitute a different blade."

If the artifact is temperature-related, he says, "My quick fix is to dip the chuck and the tissue specimen in liquid nitrogen - which is available in virtually every dermatology office - for five to seven seconds to get it much colder, then try cutting again."

Conversely, Dr. Campbell says issues related to microtome adjustment or maintenance generally require calling a technician to troubleshoot the microtome.

"The Mohs technician can do simple things, such as trying to clean or oil the microtome. But many microtome issues require taking the microtome apart, then cleaning, lubricating and adjusting it and putting it back together," tasks which usually require a technical representative, Dr. Campbell says.

Disclosure: Dr. Campbell reports no relevant financial interests.

For more information:

http://www.mohssurgery.org/

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