Organ of the Month: Skin

The two main types of biopsy relevant to the skin are excisional and incisional. Excisional biopsies are more likely to be used to excise appreciable masses, whereas incisional biopsies are more commonly used to investigate dermatopathies. This category includes punch biopsies. For punch biopsies, there are a few golden rules to bear in mind:

a) It is fine to clip long hair with scissors but please do NOT rub, scrub or vigorously clean the skin surface – this risks losing potentially diagnostic surface material.

b) For cases with more than one lesion, take four samples using a 6mm punch. Use a fresh punch for each new case, avoid dull punches that traumatise the sample, and use the tool to cut rather than placing added pressure. [Note: We charge the same for up to five skin punch biopsies]

c) For focal lesions, two punch biopsies should be sufficient.

d) For nasal planum and footpad lesions, 4mm punches are best.

e) Avoid compression and crush artefact by scooping the sample rather than picking it up with anything such as forceps.

f) Place directly in 10% neutral buffered formalin. Do this immediately to avoid drying out. Cassettes should be avoided as they cause compression artefact too (they will turn your carefully collected sample into a waffle).

g) It is best to sample lesions earlier in the disease course (or at least a range of representative lesions). Sampling more longstanding cases carries a higher risk of capturing chronic features common to lots of conditions but specific to none. There is no need to sample normal skin and try to avoid areas of self-trauma.

h) Consider submitting one punch fresh for culture.

i) We do occasionally receive punch biopsies from known mast cell tumours, e.g. following FNA. A punch biopsy of a mast cell tumour does not really progress exploration of the case as it does not allow margin assessment or, in many cases, accurate grading. The best approach, where feasible, is complete excision and submission of the entire tumour for histopathology.

Excisional biopsy

a) For ulcers and bullae, an ellipse is better than a punch biopsy. For lesions in the subcutis, an excisional biopsy is best. Unless particularly large or likely to require surgical planning, cutaneous or subcutaneous masses should be submitted as excisional biopsies.

b) If you are interested in particular margins, please label them in some way and let us know on the submission form. You can use different suture lengths for example, or surgical ink if you have some (not normal ink, which does not survive processing). Adding a diagram to the submission form or sending images can also be very helpful. See Fig 1 below.

c) It is best to avoid making an incision into the mass. However, if you feel you need to do this to allow formalin penetration, please make the cut from the skin surface, not the deep border, as this can hamper evaluation of the deep margin. Fact sheets you may find helpful are available on our web site (please see References). They include how to send particularly large samples.