Information on the skin biopsy
The basis of dermatopathology
Fixing the tissue
Ten percent buffered formalin is generally
used to fix excidates. Formalin fixing is avoided for direct
immune fluorescence or swift incision examinations, with the
result that it is performed at the cost of severe artifacts
that impair the ability to make a histopathological assessment.
When formulating more simple questions such as demarcating
a melanoma of basal-cell carcinoma or vessel tumour, an assessment
is nonetheless possible. When formulating more difficult questions,
the more frequent avoidance of formalin fixing increases the
probability of faulty diagnoses. This applies for example
to swift incisions to demarcate a melanoma of a melanocytory
birthmark, or for cutting-edge checks on basal-cell carcinomas.
Recognising the slightest discharge from a sclerosing basal-cell
carcinoma can be difficult even when there is optimal fixing:
in a rapid-incision preparation it is often impossible. The
same applies to 
demarcating
small agglomerations of a basal-cell carcinoma of follicle
structures. The
large tissue
blemishes after operating a seemingly small basal-cell carcinoma
using the microscopically-controlled “Mohs surgery”
certainly results in part from a faulty interpretation of
initial follicle cuts, with the result that further incisions
are made, despite the completely successful removal of a basal-cell
carcinoma. Since the formalin solution used for fixing is
frozen at -11°C, 95% ethanol should be added in the ratio
of 1 to 10 for distribution in the winter. To distribute material
for the direct immune fluorescence, various buffer solutions
were recommended.(16) Containers with suitable fixing media
were generally provided at dermato-pathology laboratories.
The amount of the fixing medium should correspond to approx
20 times the excidate volume.(4) A suitable formalin tube
should be used for each piece of tissue. Even in cases where
a clinical diagnosis appears to be straightforward, such as
in suspended fibromas, errors do occur, and occasionally an
exophytic
malign tumour is discovered underneath a large
number of fibromas, whose exact location can no longer be
determined if a formalin tube alone has been used. The removed
piece of tissue must be transferred to the container filled
with formalin with great care. It is now necessary to establish
that the piece of tissue really is floating in the formalin.
Not infrequently, the biopsate remains clinging to the upper
edge of the containers, and consequently arrives at the laboratory
unfixed or is
crushed
when screwing the cover down. In either case, it
is hardly possible any longer to perform a histopathological
assessment.
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