Filtration in Surgical Pathology

The biopsy specimen should be submitted completely. It must not be damaged in any way and, of course, the biopsy ought to be processed as quickly as possible. It is too obvious to discuss, but there are other details that are significant in daily practice. Often the biopsy specimen contains numerous fragments that require a cumbersome transfer in the processing cassette. The mucus presents still another problem. Sometimes the specimen parts are almost invisible or extremely fragile. The best answer to these problems is FILTRATION.

While working with different kinds of filtration bags, I gradually abandoned them due to the inconvenience of most of them in handling. The main problem is the tendency of the specimen to pop out during embedding. The mach cassette (Biopsy Cassette) is not helpful in most cases do to some difficulties to take the specimen out during embedding. The employment of a mash cassette is reasonable in bone marrow aspirates because they filtrate slowly.

Filtration directly into the cassette through the lens paper is the safest and quickest method. The main determining factor for the method of filtration is the amount of the fluid in the container.
Small amounts of content can be filtrated using one or two layers of blotting or very porous filter papers. The widely used White (often gray) Multifold Towels are adequate.
A moderate amount of the container’s content (the majority in general practice) requires a device that can hold the cassette during filtration. A variety of holders can be used.
I used a self-made gadget that includes two plastic containers of different sizes in diameter, but of equal height. The internal container has two cutout sections in which to place the cassette. The external container supports the cassette lid. This device allows the technologist to work using both hands.

The large volume containers are difficult to use for filtration. Filtration of a large volume requires strainers with a metallic wire mesh in case the cassette twists or the contents overflow. A urology stone interceptor is not a bad device for the filtration of a large amount of fluid.

A completely different option for filtration is a disposable diaper. A piece of a disposable baby diaper as a background can substitute previously described methods in most of the biopsy cases.

I use a square or rectangular pad that is cut from a baby diaper and placed on the bottom of an empty standard glass slide box. A cassette with a moistened lens paper is placed on the wet diaper fragment. The cassette lid rests on the border of the box, freeing my hands to operate. The excess water is discarded. One pad is effective for four or five filtrations.

The brand of the diaper does not matter substantially. Ironically, the cheapest brands are the most effective. What does matter is the permeability of the paper in the cassette.

While experimenting with lens papers for filtration in the cassette, I could not find a substantial difference in permeability among the brands. Completely different permeability has the internal layer (one of four) of a Kimberly-Clark TECNOL FLUIDSHIELD surgical mask. The web of its fabric has bigger spaces between threads than the lens paper (they are definitely seen under the microscope low magnification). The speed of filtration increases dramatically, for example in bone marrow aspirates or mucus content of the specimen. The mask’s internal layer is also more convenient during processing and embedding. The disposable mask is in every laboratory supply. I use this kind of filtration paper from discarded masks more and more. Perhaps, a manufacturer might produce the filtration material at the commercial level like Allegiance’s books of lens paper.

(See also The Diaper Pad for Filtration in Surgical Pathology in the link Instruments & Gadgets).

Filtration directly into a cassette, especially with the employment of a baby diaper pad, may be a methodological step ahead in surgical pathology grossing. This method allows a faster processing of a biopsy if there are many fragments, without or with minimal handling of the specimen by instruments, thus preventing damage and contamination. The main advantage is the complete submission of the specimen. Otherwise the completeness of submission is left more or less to the discretion of the grossing technologist. Filtration will eventually be the standard procedure of processing of small biopsies.

CAP TODAY, September 2003, Innovations in Pathology.




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