Skin biopsy techniques in general practice

Types of biopsy

Skin biopsy is performed to remove a lesion or to 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, which involves taking a small disc of full thickness skin using a special punch biopsy instrument.

• Shave biopsy, which 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. This is occasionally used in specialist centres but not often in general practice.

General considerations

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 the separate article Minor Surgery in Primary Care.

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 separate article Medical Ethics).

• Local anaesthesia techniques.

• Infection control.

• Staff training.

• Audit.

• Premises.

• Handling and collection of specimens.

Techniques

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 excisional 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.¹
  

• 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 (relaxed skin tension lines) are also important and generally now preferred.² This can be appreciated by examining parts of the body. Remember that lesions have three 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 biopsy³

• 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. A 4 mm punch is sufficient for non-facial lesions. In granulomatous conditions or conditions with atypical features, 5 mm biopsies are preferred. Biopsies of less than 3 mm may be difficult to process for histology.

• Having achieved local anaesthesia, stretch the skin at 90° to the tension lines. Rotate the skin punch into the dermis, being sure to obtain 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.

• A punch of 3 mm 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 keratoses.⁴

  • 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

• 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 immunofluorescence 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 immunofluorescence should be examined within 36 hours.

• Make sure that the container is properly labelled and, on the request form, give as much information as possible. See this as a doctor-to-doctor referral to an histopathologist. The more the histopathologist knows about the patient and the specimen, the more helpful he or she can be. If available, a rubber stamp to illustrate the site of the lesion can be helpful.⁵ A picture paints a thousand words.

• There has been pressure on GPs from NHS managers in some areas to be judicious about the use of sending skin lesions for histology where the risk of malignancy is low. There is no consensus among clinicians: some send all lesions; others are more circumspect.⁶

Management of suspicious malignancy

Most skin lesions removed in general practice will be benign. This remains true, even though the incidence of skin cancer is rising, because increasing public awareness results in a proportional rise in the number of patients consulting with benign lesions.⁷

The confidence and competence of GPs is influenced by training and experience. There is evidence for increased recognition of melanoma after training but this only persists only in the short-term and regular updates may be required to maintain skill levels.⁸ In countries with a high prevalence of skin cancer, GPs will gain more experience of diagnosing and treating skin cancer.

Where malignancy is suspected, urgent (2 week wait) referral is usually the most appropriate course of action. When removal is undertaken for some particular reason, it should be within the clinician's usual scope of practice, eg, by a GP with extended role. It is generally the best policy to attempt to remove all of the lesion with an appropriate margin. Lesions must not be treated by destructive techniques such as electrocautery because this technique does not allow histological diagnosis and confirmation of complete excision.

• Basal cell carcinoma is suitable for biopsy, even punch biopsy, although excisional biopsy with a margin may be better. One study found that punch biopsy can result in underdiagnosis of aggressive subtypes.⁹ Complete conventional excision is associated with a very low rate of recurrence over the subsequent five years.¹⁰ What the margin should be is a matter of some debate.¹ In an analysis of peripheral and deep margins of histological clearance, around 1,539 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.¹¹ One study found a high rate of recurrence after incomplete excision and recommended immediate re-excision unless there were medical contra-indications, in which case regular follow-up should be instituted.¹² It should be remembered that in completely removed basal cell carcinomas, apparent recurrences may well be new primaries.¹³ Lesions in the head and neck region are at more risk for recurrence, when compared to lesions in the trunk and extremities.¹⁴

• Squamous cell carcinoma of skin may be suitable for punch or excisional biopsy if small. Again, excision margins are a subject of debate. A 5 mm margin has been suggested.¹⁵ Incomplete excision in the head and neck areas is common and these should generally be referred for excision.¹⁶ The National Institute for Health and Care Excellence (NICE) recommends that non-healing lesions larger than 1 cm with significant induration on palpation, commonly on the face, scalp or back of hand with a documented expansion over eight weeks, may be squamous cell carcinomas and an urgent referral should be made. Patients with histologically proven squamous cell carcinoma should be referred urgently.¹⁷
  

• Malignant melanoma of the skin, if suspected, should be referred urgently to a dermatologist. Guidelines recommend that excision should not be attempted in primary care.¹⁸ Amelanotic lesions can be a particular problem.¹⁹

Audit

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?