Information on the skin biopsy

The basis of dermatopathology

Orientation of the tissue in the laboratory

It should be possible to distinguish the topside from the underside of material arriving at the histo-pathological laboratory. Only in this way will we be able to orient the tissue when embedding it, in such a way that all removed layers of skin are well-represented in the incision preparation. When performing shave, punch and spindle biopsies, an orthograde initial incision is generally facilitated. Orientation of the material becomes more difficult if the pieces of tissue are of the same length on all dimensions. This arises especially in the case of small punch biopsies, where a 2 or 3mm punch has not been pressed sufficiently deep into the tissue. If such small, flat excidate has been subject to a bad initial incision, for example tangentially, without representing the epidermis, subsequent embedding is seldom successful due to its small size. In the case of small biopsies, the diameter and depth should be as distinct as possible. If greater depth is being sought, smaller punch biopsies should be performed; if a larger diameter is needed, shave biopsies using a scalpel or – where there are changes in skin level – a razor-blade or sharp ring curette.

Excision biopsies of tumours are always checked for completeness. Where there is focal formation of tumour agglomerations at the edges, it may be essential to locate these precisely. This does not as a rule apply to small spindle excisions, since if an after-excision becomes urgently required, the entire scar will be cut round in any case. For larger biopsies, the precise location details of tumour agglomerations forming at the edges allow well-targeted after-excisions. This is possible only if the topographical position of the excidate can be verified in the laboratory. Where there are asymmetric excidates, a small sketch will suffice: for symmetric excidates, however, one side of the preparation needs to be marked: this is normally done using a thread marker at the cranial pole (at the top). In so doing, care should be taken that the thread is attached loosely – if possible by forming a loop, since the tissue worked upon must be removed again. If the knot is tied up to the excidate too tightly, removal of the thread not infrequently causes artifacts, whereupon the ability to assess the excidate is impaired, especially in small biopsies. After removing the thread, the excidate is marked in the laboratory with distinct colours and then cut up crossways into grades for colour-coding. In this way, we will be able to provide the precise location in the event of formation of tumour agglomerations at the edges. (18)

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