Skin Biopsy Techniques in General Practice

Skin biopsy is performed to remove a lesion or take a diagnostic sample of a skin rash, or lesion with subsequent examination of tissue using a variety of possible staining and microscopic techniques. The techniques most often employed are:

• Incisional biopsy when skin is removed using scalpel incision. This may involve taking part of the skin or removing a complete skin lesion (excision biopsy).
• Punch biopsy involves taking a small disc of full thickness skin using a special punch biopsy instrument.
• Shave biopsy involves removal of protruding, superficial skin blemishes (for example skin tags).

Other techniques include:

• Curettage (with cautery). This may be used with superficial lesions to remove and sample lesions. It is combined with cautery or cryotherapy.
• Needle biopsy is occasionally used in specialist centres but not often in general practice.

Such procedures are often carried out in general practice. Standards have been set and guidelines produced on how personnel, premises, procedures and equipment should be organised. These are outlined in Minor Surgery in Primary Care - Basic Procedures, Minor Surgery Procedures in Primary Care and Infection Control and Instrument Sterility for GP Minor Surgery.

It can be appreciated from these articles that there are a number of important issues to be considered before undertaking these techniques. These include:

• Consent (see also Medical Ethics)
• Local anaesthesia techniques
• Infection control
• Staff training
• Audit
• Premises
• Handling and collection of specimens

Incisional biopsy

• If the lesion is large and malignancy is not suspected it is acceptable to perform an incomplete excision. This is often called an incision or incisional biopsy. It is usually recommended that the specimen include an area of normal skin.
• An excision biopsy should aim to remove the whole lesion, especially if malignancy is suspected, with an edge or margin of normal skin included around the lesion. The size of this margin is the subject of some debate in the case of melanoma and suspected melanoma.
• Most lesions are round (or nearly so) but an ellipse of skin has to be removed to obtain satisfactory closure. The long axis of the ellipse should be in the direction to produce the best scar. Langer's lines are a useful guide but wrinkle and contour lines are also important and generally now preferred.¹ This can be appreciated by examining parts of the body. Remember that lesions have 3 dimensions and it is important to biopsy deeply enough, usually including some subcutaneous fat. Sometimes this requires resorbable sutures to be buried in the fat layer to get good apposition. A few neat silk or vicryl sutures are usually the best way to close the skin.
• Be sure to get an adequate specimen and handle it with care as crushing it will make histological interpretation more difficult.

Punch biopsy

• This is not used very often in general practice. Patients will usually have been referred to a dermatologist and punch biopsy is used when a full thickness biopsy is required. It will usually be used for benign rashes and skin disorders to assist diagnosis.
• The instruments for punch biopsy come in various sizes and are usually 2 to 8mm in diameter. Choose an appropriate size.
• Having achieved local anaesthesia, stretch the skin at 90º to the tension lines. Rotate the skin punch into the dermis, being sure to get an adequately deep specimen. Remove the punch when it enters the subcutaneous fat and beware of underlying structures such as nerves or vessels. Raise the specimen above the incision. A 21 gauge needle is advised rather than forceps that may crush the specimen. Cut the specimen free with tiny iris scissors.
• Normally a 2 or 3mm punch does not require a suture to the skin but a larger one will need 1 or 2 sutures to close the wound and possibly to aid haemostasis.

Shave biopsy

• This is used with protruding skin lesions such as skin tags, actinic keratoses² and seborrhoeic keratoses. It can be used for basal cell carcinomas.
• It usually requires local anaesthetic.
• It can usefully be combined with cautery to arrest bleeding and promote healing.
• After cautery a plaster can be applied.

• Specimens should be handled with care and if more than one is taken it is imperative to label which is which. If the report says that it is an incompletely excised malignancy, it is necessary to know which site this referred to. Specimens should be placed in a container and covered liberally with 10% formalin to give free immersion. The exception to this is specimens for microbiology that require the appropriate transport medium and specimens for immunofluoresence that require a specific medium. If there is any uncertainty then discuss it with your local laboratory.
• There is no hurry to get specimens in formalin to the laboratory but specimens for microbiology should arrive as soon as possible and specimens for immunofluoresence should be examined within 36 hours.
• Make sure that the container is properly labeled and on the request form give as much information as possible. See this as a doctor to doctor referral to a histopathologist. The more he knows about the patient and the specimen the more helpful he can be. If available, a rubber stamp to illustrate the site of the lesion can be helpful.³ A picture paints a thousand words.
• Some authorities advise that anything removed at minor surgery should be sent for histology. If there is any doubt about the diagnosis this is wise but when the doctor has no doubt about the clinical diagnosis it does seem extreme. Sending skin tags for histology is a waste of time and money and valuable resources. A Dutch survey found that there was often discrepancy between clinical and histological diagnosis.⁴ The figures were 31% for GPs, 32% for surgeons and 17% for dermatologists. It would seem that an appropriate policy is the very liberal but not invariable use of histology.

Most skin lesions removed in general practice will be benign.⁵ The confidence and competence of GPs is influenced by training and experience. In countries with a high prevalence of skin cancer GPs will gain more experience of diagnosing and treating skin cancer.
Where malignancy is suspected the best policy is to attempt to remove all of the lesion. They must not be treated by destructive techniques such as electrocautery as a histological diagnosis and confirmation of complete excision is required.

• Basal cell carcinoma (BCC) is suitable for biopsy, even punch biopsy although excision biopsy with a margin may be better. Complete conventional excision is associated with a very low rate of recurrence over the next 5 years.⁶ What the margin should be is a matter of some debate.^7,8 An analysis of peripheral and deep margins of histological clearance around 1539 consecutive basal cell carcinomas excised by conventional surgery showed that 81 lesions (5.3%) were incompletely excised peripherally; 36 lesions (2.3%) were incompletely excised deeply; 13 lesions (0.8%) were incompletely excised peripherally and deeply.⁹ Incomplete excision requires appropriate follow up with further excision, radiotherapy or even observation and the outcome can be excellent.¹⁰ It should be remembered that in completely removed BCCs apparent recurrences may well be new primaries.¹¹ Lesions on the head and neck have a higher rate of incomplete excision and other risk factors have been identified.¹² Lesions with a high risk of recurrence or incomplete excision should be referred.
• Squamous cell carcinoma of skin is also suitable for punch or excision biopsy. Again excision margins are a subject of debate. A 5 mm margin has been suggested.¹³ Incomplete excision in the head and neck areas is common and these should generally be referred for excision.^14,15
• Malignant melanoma is suitable for an attempted wide excision but punch biopsy should not be useD as it makes it impossible to stage the lesion. It is not uncommon to find that excision is incomplete. This does not matter if it is followed by referral to a plastic surgeon who will perform the necessary surgery. A survey from London found that GPs often failed to excise the whole lesion and that a confident diagnosis was made in only 17% before operation.¹⁶ Amelanotic lesions were a particular problem. A survey from Edinburgh concluded that general practitioners need to think more often of malignant melanoma when they excise pigmented lesions and when they consider this tumour a possibility should perform an excision biopsy with a lateral clearance of at least 2 mm.¹⁷ However much wider margins of 2 cm are likely ultimately to be required.^{18,19,20,21,22} Better results are claimed by dermatologists in one study comparing dermatologists, surgeons and GPs.²³

Minor surgery as a whole is a very suitable area for audit and is actively encouraged in the new guidelines.

• How many procedures were performed in the year and in which category?
• Who performed them?
• How many were not done in the practice but sent elsewhere?
• In how many was there a tissue diagnosis?
• Did it confirm the clinical diagnosis?
• How many were malignant?
• Review all complications. Is there a pattern that suggests that clinical protocols should change?
• Is there a pattern that suggests that an operator should refrain from minor surgery or undergo further training?