All lesions that may be cancerous should be biopsied, meaning all or part of the lesion should be removed for analysis. It is advisable to do a biopsy if the diagnosis is unclear.
For diagnosis using a punch biopsy:
A punch biopsy is performed using a small circular knife that cuts a cylinder of tissue. The size is usually 3mm but it can be up to 1cm in diameter, and the cylinder delivers a representative specimen of the lesion in question.
Typical indications for a punch biopsy include rashes or blisters, or pigmented skin lesions persisting for longer than two weeks or which do not respond to other treatment. These may be malignancies such as cancers of the skin, or involvement of the skin with blood cancers; or, more commonly, infections of the skin, or auto-immune diseases, such as psoriasis.
For diagnosis and treatment using an excision biopsy:
A formal skin biopsy removes either the entire lesion or a representative part of it. Typical indications included pigmented lesions such as moles, persistent ulcers, skin tags and warts.
Contraindications and other considerations
All biopsies leave scars. Lesions involving the eyelids and nose, as well as palms and soles, should be biopsied by dermatologists or plastic surgeons.
Patients on warfarin, or who are known to have bleeding disorders, need a check of their clotting profile before excision biopsy.
Patients on aspirin must be managed with careful attention to bleeding, and pressure bandages.
Skin antiseptic like isopropyl alcohol, povidone-iodine or chlorhexidine is used to prepare the site.
Generally, local anesthetic such as lignocaine is used. Lignocaine is a vasodilator, and to counter this effect, preparations including adrenalin can be used.
The local anesthetic is injected in and around the lesion, as well as deep to the lesion.
For the punch biopsy, the skin is slightly stretched perpendicular to the normal skin tension lines. This will cause an oval rather than a round lesion, facilitating wound closure. The punch is placed perpendicular to the skin, and constant pressure is applied with a circular motion. Once a depth of about 5mm is reached, the punch is removed and the specimen retrieved.
For an excision biopsy, incisions should be placed along natural creases or, in the extremities, along the longitudinal axia of the extremity. This ensures that definitive therapy in case a cancer is diagnosed, is not compromised.
For closure of the wound, dissolving sutures should be used so that the patient does not need to return to have the sutures removed.
Wounds are usually covered with an occlusive or semiocclusive dressing; patient can shower with these dressings, but should not swim or bathe for at least 24 hours.
A follow-up date is usually arranged with the patient to discuss the results.
With pigmented lesions, one has to consider the possibility of malignant melanoma.
Small lesions can be removed with a punch biopsy, provided the lesion can be completely removed. Larger lesions need excision biopsy. The lesion must be removed at the level of the subcutaneous fat to allow for proper assessment of how advanced the lesion is.
When melanoma is diagnosed, the tumour-free margin is determined by the depth of tumour invasion, which can imply re-excision of the scar with a wider margin, as well as to the level of the deep muscle fascia.
Bleeding, infection and allergic reactions are all possibilities.
Bleeding can usually be managed by applying pressure, adding an extra suture or by opening the wound to identifying the bleeder, and tying it off.
Infection is usually the result of staphylococcus or streptococcus. If the infection is localised to the wound, treat locally by cleaning the wound and - if no response is obtained within 12 hours - the wound should be opened and allowed to heal on its own with daily dressings. Antibiotics are needed only if there is fever or other sign of systemic infection.
Allergic reactions are usually due to the dressings.