HOW TO PREP AND CUT: Biopies

Occasionally, the doctor may find a suspicious spot and will want to do a biopsy before going ahead with Mohs. Instead of the usual horizontal sectioning, biopsies are sectioned vertically. You may have heard it referred to as "bread-loafing."

A biopsy can reveal whether there are any cancer cells present and can help differentiate between the various types of cancer. It will not, however, tell you WHERE those cells are or if the margins are clear. 

There is no need to bisect or ink the tissue because you will be cutting through the entire piece. Squeeze some OCT onto a disc on the cold bar. Once the base of the OCT has turned white, hold the biopsy specimen vertically in the OCT until it's frozen enough to stand up on its own. Add more OCT on top so that none of the tissue is exposed.

Don't worry about lining it up perfectly, just eyeball it and do your best. The FBX slide must show sections from the entire specimen, so you'll be cutting through quite a bit of tissue in between the sections that you actually pick up. Advance the wheel manually several times then use the hand-crank wheel to discard a few regular cuts before picking up a nice wafer.

As always, be careful that the tissue sections are not placed on top of OCT from a previous section or it will all wash off in the stains. There won't be any tissue left to do a recut!

Repeat until you have at least 8 sections and you've cut through the entire biopsy specimen. Stain as usual.

Large Biopies
If you get a biopsy that's bigger than usual, you can save time by bisecting it and placing the halves vertically on a slide. Freeze the back of the slide and make a regular mount as if you're processing a normal mohs specimen. Since the piece is now essentially half the depth, you won't waste as much time cutting through the specimen to get your 8-10 sections.

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.

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.