A skin biopsy is basically a very small sample of skin that is removed by a doctor so that it can be examined in a lab to determine what cells it is made up of.
Skin lesions (lumps, bumps and other changes) are very common things for a person to present to their GP with. While many of these are harmless, they can be cosmetically displeasing and many have the potential (however unlikely) to develop into something more serious. As such, all skin lesions should be investigated or removed if the general practitioner has concerns about it.
For many skin lesions, such as skin cancers, the first treatment is surgical removal. This is because it does not only provide a definitive diagnosis, but is also the most effective treatment. For some lesions however, it is necessary to take a small sample of the tissue before proceeding with treatment. The name for these ‘small samples’ is a biopsy, and so a skin biopsy is just a small sample of skin that is removed and sent to a lab for further analysis.
A skin biopsy may be done because the treatment will be very different depending on what the lesion turns out to be, or it may be that the doctor has to be very sure it is worth removing, such as if removal would require extensive surgery on a sensitive area such as the face.
The information that can be obtained from a skin biopsy would include things such as what type of tumour or problem is within the lesion, what types of cells make up the lesion and how they look, as well as confirming that all of a tumour has been removed.
A shave biopsy is a technique where the very surface layer of skin is ‘shaved’ off by using the blade of a scalpel. It does not get a very deep sample of tissue, and so may not be the right technique for some skin cancers that go deeper into the tissue. However, it is very useful for taking samples from large areas, where tumours are present in a few different sites or have borders that aren’t very clear.
Some people say that a shave biopsy should be done with caution on pigmented (coloured) lesions. This is because if the lesion comes back as being a melanoma then the shave biopsy can cause some trouble with finding out further information about the lesion. While some people hold to this belief, others say that a shave biopsy can be a very useful tool in pigmented lesions.
A shave biopsy will consist of the following steps:
- Firstly, the area will have a small amount of local anaesthetic injected into it to numb it.
- The actual removal of the lesion can be done in a few different ways:
- Very sharp special scissors can be used to remove the lesion.
- A scalpel blade held along the surface of the skin can be used to remove the lesion.
- A razor blade can be slightly bent, with the sharp edge running underneath the lesion to remove it.
- If there is any bleeding, then diathermy (where an electrically charged piece of metal creates a very minor burn) or a substance called ‘ferrous sulphate’ can be used.
Generally, a shave biopsy will heal very well, with little bleeding and usually no scarring. In fact, it can heal so well that sometime a doctor will have to note down or photograph the area as it will be impossible to tell where it was taken from by the time the results come back!
A punch biopsy involves the removal of a small piece of tissue using a circular blade that is usually attached to the end of something that looks like a plastic pencil (similar to the diagram, right).
It is very commonly used in general practice because it is quick, easy, causes little to no scarring or bleeding and also gives a sample of the whole thickness of the skin, from the surface to the fat, and so is great for working out a diagnosis.
A punch biopsy is mostly used when a doctor is a little uncertain about what the lesion is. This usually means that there is a possibility that the lesion is a cancer of some sort, but the doctor is not one hundred percent certain and does not want to remove it without checking first.
A punch biopsy can be used, for example, to tell whether a mole is simply a mole or actually a melanoma. Usually the sample will be taken from the area that looks the most ‘suspicious’.
Other indications for a punch biopsy include in the investigation of:
- Skin cancers such as basal cell and squamous cell carcinomas of the skin;
- Bullous skin disorders (where the layers of the skin surface break apart, and the ‘gap’ between them fills with fluid);
- Inflammatory skin conditions; and
- Odd looking lesions with an unknown cause.
The doctor will do the following during a punch biopsy:
- Firstly, they will clean the skin.
- Then they will inject the skin with a small amount of local anaesthetic to numb the area.
- After the anaesthetic has fully numbed the area, the doctor will gently hold the skin tight, so that it does not move.
- They will then take a small ‘punch’ with an object that looks like a pen with a small cylindrical blade at the end, and hold it vertically over the skin area.
- The doctor will then place the blade over the skin and rotate, creating a small circular cut.
- They will then remove the blade and pick up the piece of skin inside the cut with small forceps (surgical tweezers).
- The doctor will then cut the base from under the sample using a scalpel.
- The sample will then be placed in a fixative to be transported to a lab.
- The doctor will stop any bleeding by placing pressure on the site before applying a dressing, or putting in a single stitch to close the hole.
A punch biopsy is almost completely safe to do, and the only worry with doing one is that there will be damage to the tissues that lie underneath the biopsy site. These areas are places like the eyelid, the back of the hands in elderly patients, the fingers and the part of the cheek that is just under the eye.
A doctor will use their judgement to decide on where it is safe to do it, and in the vast majority of cases there is nothing to worry about.
A surgical biopsy is often the first step for a skin lesion, as it provides both a very good method of diagnosis along with actually being one of the most effective treatments.
Sometimes a surgical biopsy can remove the entire lesion, and this is called an ‘excisional’ biopsy. Other times, only part of a lesion may be removed so that it can be sent to the lab for further diagnostic tests and this is called an ‘incisional biopsy’.
There are several reasons for a surgical biopsy:
- Basal cell carcinomas and squamous cell carcinomas can be very effectively treated with a complete surgical excision.
- Removal of pigmented lesions can both identify melanomas as well as get information regarding its depth.
- Almost any lesion that cannot be adequately assessed or treated by punch or shave biopsy often requires a surgical biopsy.
Firstly, the doctor will want to very closely examine the lesion to see just how big it is, whether it is a small lump or is irregular etc. so that they have a very good idea what needs to be removed. As this is a surgical excision, the area will be cleaned with some surgical-strength cleaning agents such as chlorhexidine or iodine, and usually a surgical drape (which can be plastic or cloth) will be placed around the site.
Next, the doctor will probably (but not always) draw out the area that needs to be removed. The best shape for a cut is an ‘ellipse’, although actually it’s not a true ellipse because it is pointy at both ends. This shape allows for the best healing. Usually the ellipse will be about 3 or 4 times as long as it is wide. The general shape and usual features of the cut are seen in the diagram to the right.
The ellipse is usually placed so that the longer length runs along the skin creases. This is because the skin creases mark out areas that are under lower tension, and so there will be less stress on the wound afterwards causing a better outcome with less pain and scarring.
Following marking out the area, it will be infiltrated with a local anaesthetic until suitably numb. The skin will then be cut using a scalpel, following the markings. This will be cut down to the layer below the skin – the subcutaneous (which means literally, ‘below the skin’) fat. This will form a little ‘island’ of skin that is completely separate from the area around it. This ‘island’ will be lifted up with some forceps and a scalpel will cut away any connections. Of course, due to the anaesthetic, you will not be able to feel any of this.
This sample will then be taken away, put in a fixative and sent off to the lab. At the lab, they take very fine slices from the lesion, add some special dyes so that the different types of cells stand out, and then put the sample under a microscope (they do this with the other biopsy samples as well). While the resulting slide may look very confusing, to a trained eye it reveals many things. An example slide (with some features pointed out) is shown below.
After the lesion has been removed, the doctor will put in some stitches. They may put in a stitch that sits below the skin which dissolves: this stitch helps to stop bleeding and prevent the formation of a ‘haematoma’ (a collection of blood beneath the skin). Some doctors use an antibiotic ointment over the site, however this is not necessary to obtain adequate healing. After this, a dressing will be placed over the area, and it’s all done!
Removal of the sutures will depend on the site in which they have been placed. In areas with significant skin tension like the back, they may be left in place for up to 2 weeks, whereas in more delicate areas such as the face and hands, they can often be removed after as little as 5 days.
- Australian Cancer Network Management of Non-Melanoma Skin Cancer Working Party. ‘Clinical Practice Guidelines Non-melanoma skin cancer: Guidelines for treatment and management in Australia’, Cancer Council of Australia, 2003.
- Murtagh, J. General Practice (Third Edition), Sydney: McGraw-Hill 2005.
- Zuber TJ, Mayeaux EJ. Atlas of Primary Care Procedures, Philadelphia: Lippincott Williams & Wilkins 2004.