Tierdermatologie Deisenhofen Consultations
Seven tips to obtain a better skin biopsy result:
1. Do not prepare the skin surface (except nodule excision & deep tissue culture)
2. Spend 5 minutes looking for primary lesions to biopsy
3. Think about the differential diagnoses and write them on the submission form
4. Select multiple samples (4-6) that represent a range from normal to worst
4. If possible, always include a normal sample from the lateral or dorsal trunk
5. Use 6 to 8mm punches or an excisional biopsy except on noses and feet
6. Handle the biopsy specimen carefully, treat it like tissue paper even when excising
7. Give the pathologist a complete history, physical findings as well as your differential
Please see below for some more detailed biopsy sampling guidelines
A skin biopsy is a "snapshot", a movie "freeze", a picture taken at one point in time:
It may help to remember that a skin biopsy is a selection of several areas of skin
(which one hopes are representative of the range present) at a single point in time
(the time of the biopsy sampling). It may be that this timepoint is not optimal with
regard to the pathogenetic events. For example in pemphigus foliaceus, it may be that
the actual acantholytic pustule formed and ruptured a week ago and there are now no
diagnostic acantolytic pustules to be seen! The pathologist must then work with
supportive clues, such as acantholytic cells in the crusts, rather than more specific
Detailed biopsy sampling guidelines:
Which skin lesions should be biopsied?
Any skin lesion which appears unusual, especially if the onset is acute; lesions which
fail to respond to empirical therapy; lesions that are nodular and those in which a
diagnosis of neoplasia is suspected. Finally biopsies can be helpful to exclude
diagnoses, even if one does not necessarily obtain a definitive diagnosis
Preparation of the site
With the exception of excisional biopsy of nodules, no surgical preparation of the
site should be employed. Even topical application of alcohol with air drying may alter
the epidermis. The overlying hair is clipped and gently removed. If crusts are present
it may be less traumatic to use scissors than electric clippers,as they should be left
on the skin, biopsied and a note 'please cut in crusts' should be added to the request
form. Local anaesthesia can be administered subcutaneously with the needle entry
point outside the biopsy area. Infection as a result of this lack of surgical preparation
Selection of the site
Spend 5 minutes looking for primary lesions and the full range of lesions. Carefully
examine the entire animal for the most representative samples, and try to form a list
of differential diagnoses prior to biopsy. Sample depigmenting lesions in an area of
active depigmentation i.e. a grey color rather than the final stage of depigmentation
which is white.
Sample alopecia in the centre of the worst area as well as in junctional and normal
areas. Before the biopsy, draw a line on the skin in direction of the hair growth.
Sample areas of ulceration via an elliptical biopsy with the adjacent intact skin. The
transition point between ulcer and intact skin may give clues for the cause IF it is to
do with an epidermal disease such as a bullous dermatosis.
Always include a normal sample, if possible from the dorsal trunk, not ventrally.
Obtain multiple samples (6 is a good rule of thumb) so that they represent the range
of lesions from normal to worst.
Handle the biopsy specimen carefully, treat it like "tissue paper" even when excising.
The biopsy punch is held at right angles to the surface of the skin and gently placed
over the selected lesion. Firm continuous pressure is applied and the punch is rotated
in one direction (!) until a sufficient depth has been reached to free the dermis from
its underlying attachment. The punch is removed and any blood carefully blotted. The
section of tissue is grasped gently at the base - which should be the panniculus - and
subcutaneous attachments severed. Under no circumstances should the dermis or
epidermis be grasped with forceps as this leads to 'crush artifact', destroying the cells
and architecture of the sample.
In the case of a thin sample, it should then be placed - panniculus down - onto a rigid
piece of cardboard or piece of tongue depressor. This prevents the tissue from curling
when placed in the formalin. Wait two minutes for the tissue to dry onto the
cardboard a little and then place it tissue side down, cardboard side up in the
formalin. The volume of formalin required is approximately 10 times the volume of the
sample. Large nodules can be partially transected @ 1cm intervals to allow adequate
penetration of the formalin into the centre of the lesion - but most important!! -leave
the base of the nodule attached, do not cut completely through the nodule, so that
the architecture is retained.