HOW TO CUT: Fat

Fatty tissue is, without question, the arch nemesis of the Mohs tech.  There you are, cutting beautiful sections of non-fatty tissue when that spot of fat hits the blade and BOOM!  
It melts away, leaving a gaping hole in your section and a smudge of yellow mush on your blade.  

The problem is simple: Fat does not freeze well.  It takes a great deal more time and LN2/Freeze-It to reach the optimal cutting temperature.

Unfortunately, the temp at which fat hardens is often too cold for obtaining good sections of the non-fatty tissues that may also be present in the same sample.  If this is the case, you can use your A slide to get several cuts with full epidermis and then work on the fat for the B slide.

Step 1 - A sharp blade and a clean stage.

If your blade is getting dull, this is the perfect time to put in a new one.  The knife stage should also be free of any frost, OCT, streaks of tissue, and clumps of melted fat.  Use a piece of dry gauze to wipe residue up and away from the blade.  

Step 2 - The fat must be EXTRA COLD.

Once the tissue is lined up to the blade and you've cut through the safety layer, spray the yellowish unfrozen fat with short bursts of LN2 or Freeze-It until it turns white.  The picture on top shows fat that's a little on the warm side. (Not the best example, since I'd already frozen it and made slides for the doctor by this point)  On the bottom, the frozen fat appears more white.  The tissue may require several rounds of spraying with the LN2 before it's finally ready to cut, so patience is a must.  It's better to take an extra minute with this step than to attempt to cut too soon and waste tissue. 

Freeze artifact
with sub-epidermal splitting

CAUTION:  Excessive freezing of the block may cause freeze artifacts such as sub-epidermal splitting or the appearance of "bubbles" due to the expansion of water in the tissue or blood.  As mentioned above, you can always make the A slide with sections of non-fatty tissue at the regular cutting temperature and the B slide with fatty sections at the colder temperature.

Step 3 - Cut THICK and FAST.

Once the fat is frozen white (and STAYS white for a few seconds) discard the first one or two wafers. Double ratchet so that your sections are ~6-8µm thick and then slowly cut through the OCT until you've cut into the edge of the specimen.  Make sure that the tissue won't roll up, then grab the edge under your brush and coordinate the speed of your right hand with the guiding motion of the brush in your left.  Do not press the brush and tissue against the stage or it will stick and you won't be able to cut anything until you clean it.  If you manage to crank the wheel in a clean, swift jerk, you'll be able to get reasonable sections of some fairly fatty tissues. 

Some rolling on the bottom edge. Oops.

Maximizing Blade Usage - GG

It is possible to use THREE sections of the blade instead of just two. When you slide the blade in, just make sure that it's parallel to the edge of the knife.  The blunt edge of the blade should fit snugly into the groove.  Use your screwdriver to double check the tightness of the top screws, and you'll be good to go!

Disclaimer: I've tested this with three different knives without any problems. I have not, however, tested it with the smaller black-top knives. Just to be safe, take a few practice cuts from the safety layer or from a tissue block that you no longer need before cutting actual slides for the doctor.

A side note: If you make really wide OCT mounts (wider than the metal disc), you probably won't get good results with this method.  All that excess OCT will dull the adjacent section of the blade and you'll only get two sharp areas of the blade before you have to change it out.

Position #1: Insert the blade just far enough to cut the block.
Position #2: Roughly in the middle. You won't be able to see either of the 2 elliptical holes.
Position #3: Move the blade all the way over until just the tail end of the blade is cutting the block.

Safety Update: In Position #3, notice how there's quite a bit of exposed blade on the left-hand side. You run the risk of cutting yourself, since your left hand is the one that's working inside the machine.  I've found that it's safer to take the blade out and flip it over so that the blade looks like Position #1 but with the circular hole on the right side.

HOW TO PREP: Dog Ears

Dog ears (aka Burow’s triangles or cones) are triangles of tissue that are removed from the sides of a circular or elliptical wound before doing a closure.  Their removal allows the skin to heal flat without puckering at the ends, but also lengthens the incision and resultant scar. 

If the Mohs surgeon is fairly certain that the next level of tissue will be clear of cancer, they may decide to kill two birds with one stone by excising the dog ears and having them processed as a level.  

You will need to show the epidermis from the two sides of the cone (marked purple in the picture) as well as the surgical margin that makes up the base of the piece.  Bisect through the apex of the triangle to get the epi around the tip to lay down easily.  From here, continue processing it like a regular Mohs level.

Understanding Mohs Micrographic Surgery

The doctor marks the location of the tumor, including a 1 to 1.5mm margin of uninvolved skin.  The patient is locally anesthetized with lidocaine and epinephrine.  The epinephrine vasoconstricts arteries, which reduces bleeding and also slows the absorption of the lidocaine, thereby prolonging the effect of the anesthesia.

The tissue is then excised at a 45° beveled edge and brought to the mohs tech for processing.  

The drawing should be in the exact shape of the specimen, and the same size or larger. The map should also show the level, piece number, nicks, orientation, and inking of the piece.  

If the doctor sees any cancer on the slide, it's location is marked on the map and another layer of tissue is removed from that area.  This procedure is repeated until no further cancer is found.  This ensures that only cancerous tissue is removed during the procedure, minimizing the loss of healthy tissue. 

Model of standard mohs levels. Will be available at the office.

Regular Cryo Maintenance: Alcohol and WD40

"Take care of your cryo and she'll take care of you." -RH

At the start of each job:
Once you've worked the microtome loose with alcohol, use a syringe to squirt WD40 in/on all of the following locations:

At the end of each job:
Spray everything with alcohol and wipe all surfaces, especially the nooks and crannies that tend to collect shavings of tissue and OCT.

TROUBLESHOOTING: How to cool a warm cryo

It's a Mohs Gnome morning.

You forgot to plug in your cryo before you went to bed, or the staff forgot to turn on the in-office cryo.  Maybe there was a power outage in the middle of the night.  For whatever reason, it's morning, your cryo is warm, and you don't have the luxury of waiting 3hrs for it to get cold.

Take a deep breath.  Here's what you need to do.

[optional] The Ice-Bag Method - MN

If your job is ≥30min away, you may want to consider using the Ice-Bag Method to start cooling your cryo while you drive.

Place bag directly on microtome.

STEP 1: Break the block of dry ice into smaller chunks. 

STEP 2: Dump everything into a plastic bag and double-knot the handles.

STEP 3: Place the bag directly on the microtome.

STEP 4: Close the lid, cover the cryo, strap it in, and get to that office!  (drive safely, of course)

30min of driving will give you a -13°C headstart on cooling, and the plastic bag will have prevented most of the frost from building up on your microtome.

The Standard In-Office Method: Dry Ice and LN₂

Most of the time, you’ll live close enough to your job that it’s best to just take your dry ice directly to the office and plug in your cryo ASAP. 

STEP 1: Get your knife into the machine so it can start cooling right away.

STEP 2: Balance the chunks of dry ice on the microtome.  Some well-placed damp paper towels will prevent the chunks from shifting and will act as ice cubes once they freeze up.  –EM, TR, CD

Caution: Make sure the dry ice doesn’t rest against the walls of the cryo or

else the Freon in the tubes will freeze solid and ruin your machine.  –BP

STEP 3: Slowly pour LN₂ over the microtome and knife.  Close the lid.  You will have to repeat this step several times before the machine is cold enough. 

The chunks are usually bigger. These have been sitting in a bag for a few hours.

Pro Tips:

Fill the "bowl" and ball joint socket with LN2.

-Use a damp paper towel to form a cup next to the knife and fill it with LN_2.  Also, keep pouring LN₂ into the socket for the ball joint. –GS

-Place the knife on the cold bar while the machine cools.  If you have a small knife, you can dunk it into the cry-ac to rapidly cool it.  You can cut with a warm machine as long as your knife is cold, but you have to be fast and use freeze spray between each cut. –GG

-Use the Quick Freeze by turning the dial clockwise from 0, where it’s usually at,
to 3. –BP, EM

-Cover up the thermostat as much as possible with paper towels/gauze so that when you pour in the LN_2, the thermostat doesn’t read the temp and shut off the machine. Not all machines have working thermostats though! –KM

-Use magic. –CS (Don’t bother asking her for the spell.  I’ve already tried.)

-Test for warm spots with dabs of OCT. (should freeze in less than 5 sec) –GG

-You can double stack two Styrofoam cups in the cryo under the blade or near the machine.  The double layer reduces the rate of evaporation of the LN₂  and allows for a cooler in-machine ambient temp. –GG

[experimental] The LN₂ Geyser Cup - GG

When you cut in a warm machine, the air makes the block sticky.  Get a urine cup, fill it with LN_2, and poke a hole in the lid.  The LN₂ will rise from the hole in a slow geyser.  Place the cup under the blade and direct the geyser towards the block.  This keeps you from needing to spray between cuts.  

If this hasn't already happened to you, it will... someday.

All About Dry Ice

Dry ice is the solid form of carbon dioxide (CO₂).  At -78.5°C, it sublimates directly into CO₂ gas instead of melting into a liquid, which makes it the perfect no-mess solution for cooling a warm cryo in a pinch.

Why does it vibrate inside the cryostat?

Compared to the ice, the metal of the microtome is HOT.  The rapid evaporation of CO₂ results in an audible vibration as the lump of dry ice hovers above the layer of gas and then falls back to the metal surface. 

Where can I buy some?  

Dry ice can be purchased from some grocery stores in 8-10lb slabs (~$1-2/lb).  Half a block should be enough, meaning you'll spend about $5-10.  It’s a good idea to call your local store ahead of time to make sure they carry it.  While one Albertsons may sell it, another may not, and you don’t want to find that out on the morning of your cryo crisis.

For safety reasons, the dry ice is kept locked up, so make a beeline to the checkout area and ask a cashier or manager-type person to get some for you.  You will need to break the block into smaller pieces to place inside your cryo.  I would recommend doing this in the parking lot rather than inside the office, since it can be rather noisy.  Besides, if you do it outside, there’s no one to witness you swinging the bag and yelling “HULK SMASH!” as the frozen block hits the cement.

full slab of dry ice

broken into chunks

Welcome back to the Mobile Mohs Blog!

First off, we'd like to thank Natasha for all the hard work she's put into the blog from 2010 to 2011 and we wish her the best with baby Coralyn! Michelle will be taking over the blog for now.

There have been quite a few changes to We Know Mohs since the last post.  the purpose of the old blog was to give tips to other histotechnicians and show doctors what Mobile Mohs is all about.  We Know Mohs is now exclusively for Mobile Mohs employees – a private space for us to share tips and techniques earned with the blood, sweat, and tears (quite literally) of all of our technicians over the past 33 years.  We’ll also throw in some pearls of wisdom, examples of good and bad slides, mohs gnome horror stories, and other mohs related tidbits.  Stay tuned!