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Institut für Pathologie - Klinikum Fürth  

Methods of Frozen Section

Introductory notes

Our department has a rather high frequency of frozen sections.
We hope that our experience may be useful to others.

The next pages contain some more or less important information about methods and philosophy of frozen section technique. But we will not and cannot fulfill all requirements and apologize for this.

The Case reports may be a help to increase diagnostic skills. We try to build up the pages that you will first see the pictures and then the clinical data. You can make your own diagnosis before considering ours.
We take responsibility for mistakes and failures; merits are pure chance.

Methods of frozen sections

Frozen sections are emergency cases for pathologists who are normally not familiar with the daily stress of surgeons. Some pathologists do not like stress and do not like frozen sections and place their lab far from the operating theatre, frequently in another building.
In these two sentences philosophy of frozen section is concealed.

1. Similar to emergency cases the frozen section must solve the most urgent problems. Only questions with relevance to the operation must be answered. Frozen section is not for the urgent surgeon who would like to know pathological findings before leaving on holiday and also not for the prominent patient in a hurry.
Nevertheless we are doing more in our department exhibiting a frozen section rate of 20-30% of all examinations. You will see our indications below.

2. Frozen sections must be quick.
The quickness depends on transport time from the theatre to the pathological laboratory (ideally in the same building by pneumatic dispatch), on pathological technique (s. staining methods) and on the experience of the pathologist.

Of course there are some other problems too. The pneumatic dispatch does not work or the porter does not find the lab. And this is also important for the surgeon: do not call your mother in-law on the same line while you are waiting for the frozen section results (an intercom system is ideal).
In our department the mean duration of a frozen section after getting the specimen is 3-7 minutes.

Indications for frozen section

Diagnostic: no preoperative diagnosis was available or an unexpected intraoperative finding (e.g. peritoneal carcinosis) must be clarified. Also resection margins may be object of frozen sections.

Several modern biological or molecular biologcal techniques require fresh tissue to examine (blots, PCR and so on). The pathologist may therefore be responsible for sampling of adequate tissue probe (the macroscopic experience of the pathologist and/or using of frozen section may be helpful to find the appropiate tissue). Receptor analysis and tissue for bacteriology also require fresh tissue.

We also examine small biopsies (obtained by endoscopy or needle biopsy) to decide whether the tissue is representative enough for further pathological diagnosis. These procedures may save the patient from a second unpleasant endoscopy and is less expensive.

Availability of frozen section

Our department offers a 24-hour-364/5-day service. The pathologist is contactable by pager and can carry out a frozen section without technical assistance.
This possibility is appreciated by the clinicians and fortunately is not required very frequently (we are a two doctor department and 15 K specimen/year).

Staining methods

The most widespread staining method probably is a modified hematoxylin eosin. It is similar to the normal one and has a duration of 1-2 min.
We prefer a polychromatic methylen blue which has a duration of 1-2 sec (after cutting a nice 4-5 slide take a cuvette of 4% methylen blue and touch the slide shortly into the fluid. Remove the excess of dye in two tap water and mount in glucose solution (5%)).
You will see: the results are good (see our case reports) but not permanent. A second slide for documentation is recommended.

We also apply a frozen section PAS to demonstrate mucin producing cells. Especially few signet ring cells (peritoneal metastasis or resection margins of gastric cancer) may make the pathologist sweat. Therefore we sweat the frozen section slides in a simple 600 W microwave oven: take out the slide and place it in a cuvette filled by 1% periodic acid. After that it is returned into the oven for 10-15 sec. It is then rinsed in dist. water and placed again in a cuvette with Schiff and put into the oven for a further 10-15 sec. Rinse again in tap water (if PAS positive material contained the water will be slightly red (and your finger)).
Counterstain with methylen blue (s. above) and you have the staining ready in 30 sec.. (Am J Surg Path 16:87-88, 1992)

The microwave oven also allows the expedituring of immunohistological stains (20-40 min). We do not use it for that purpose.

Interpretation of frozen section

As mentioned above the main indication of frozen section is to influence a surgical procedure directly.
Therefore say as little as possible and as much as needed. Heroic demonstration of your diagnostic skills is not required; however, you can demonstrate them by your simple but useful diagnosis.

Take care of the diagnosis of malignancy.
If you diagnose a malignant process a mutilating and irreversible surgical procedure may be carried out. If you make a false negative diagnosis a second operation may be required. This is the smaller evil of the two.

A last piece of advice: microscopy is not the most difficult part of frozen section. The appropriate macroscopical judgement is more important. You will only see lesions in your microscope if they are on the slide. Never let an unexperienced colleague cut the tissue for freezing! If you do though, check the specimen especially if clinical and pathological findings differ.

Good luck and less false diagnosis!
(We have about 3% depending on specimen and definition of false diagnosis.)


 
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