[Histonet] Re: clearing agent for gross specimens

[Robert Richmond]

Vinnie Della Speranza in Charleston SC asks:

I would appreciate hearing from anyone who routinely utilizes a
clearing agent in the gross room to clear fat from tissues to allow
lymph nodes to be visualized.

I am aware of Dissect Aid but would like to learn of other comparable products.
If individuals are using home made solutions are will to share their
formula I would appreciate receiving that information as well.

Our primary interest is speed of clearing for turnaround time reasons.

I am in the midst of a Histosearch search but it is slow going because
most discussions refer to tissue processing or staining so it's like
looking for a needle in a haystack.
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Most of the proprietary mixes such as Dissect-Aid and O-Fix contain
varying amounts of water, alcohol, formaldehyde, and acetic acid. As
John Kiernan pointed out some time ago, these formulas aren't very
rational. I've had good luck with both Dissect-Aid and O-Fix. When I
make my own clearing fixative, I make Davidson's fixative: 3 parts
water, 3 parts reagent alcohol, 2 parts 37% formaldehyde, 1 part
glacial acetic acid.

An obvious point often missed: you cannot post-fix. The tissues must
go into the clearing fixative before the neutral buffered formalin the
specimen arrives in has time to penetrate, a few hours but not longer.
The clearing fixative needs several hours to work, preferably
overnight, particularly since such specimens usually arrive late in
the day. The fatty lymph node bearing tissue needs to be cut up so
that the fixative will penetrate it.

Clearing fixatives are most useful with colon resections for cancer.
Mesenteric lymph nodes are often small, and very small lymph nodes
often contain metastatic colon cancer. These tiny metastases determine
treatment: chemotherapy is indicated if lymph nodes are positive.
(It's amazing that, with so much riding on it, how little attention is
paid to these details.)

In my limited experience, clearing fixatives are useful with radical
neck dissection specimens.

I don't find clearing fixatives necessary with axillary tissue removed
in the treatment of breast cancer, and the fixatives may interfere
with the immunostains often used with axillary nodes. Most
pahtologists I've spoken with about this agree with me.

I think there's a good bit of material about this in the Histonet
archives - try searching Davidson's fixative.

Bob Richmond
Samurai Pathologist
Knoxville TN