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Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z





Skin biopsy

What is a skin biopsy?

A skin biopsy is the removal and histopathological examination of a sample of skin to identify the presence, cause, or extent of a disease or condition.

Why have a skin biopsy?

One or more skin biopsies are performed to make or confirm a diagnosis, which often helps determine the correct treatment.

Choosing the site for a biopsy

It is crucial that the site of a biopsy is chosen carefully, or the pathological diagnosis could be incorrect or misleading.

Completing the request form

The clinician should ensure the pathology request form includes patient information (including age and identification details), the site and type of biopsy, time and date, clinical information and a range of possible diagnoses.

The sample pot should be labelled with patient identification details, the body site of the biopsy, time and date.

What happens to the biopsy sample?

Most skin biopsies are placed in formalin in a small pot and are sent to the lab for paraffin fixation, processing and histopathology.

Types of skin biopsy

Skin biopsy is usually undertaken using a local anaesthetic injection into the surrounding skin to numb the area. The injection stings transiently. After the procedure, a dressing will usually be applied to the site of the biopsy. This should be left in place for the first 24 hours and replaced if necessary.

Punch biopsy

A punch biopsy is quick to perform, convenient, and only produces a small wound. The pathologist can evaluate the full thickness of skin.

The disposable skin biopsy punch has a round stainless steel blade ranging from 2–6 mm in diameter; 3 and 4 mm are the most common sizes used for inflammatory skin disease. The clinician holds the instrument perpendicular to the skin and rotates it to pierce the skin and removes a cylindrical core of epidermis, dermis and sometimes, subcutaneous tissue.

A suture is often used to close the wound, or, if the wound is small, it may heal adequately without it.

Shave biopsy

A shave biopsy may be used if the skin lesion is superficial, for example to confirm a suspected diagnosis of intraepidermal carcinoma or basal cell carcinoma.

A tangential shave of skin is taken using a scalpel, special shave-biopsy instrument or razor blade. No stitches are required. The wound forms a scab that should heal in 1–3 weeks.

A scoop biopsy is a deep form of shave biopsy, used to remove a skin lesion such as a benign mole by "scooping" it out. It is also called “saucerisation” or “tangiential excision.”

Curettage

A skin curette may be used to scrape off a superficial skin lesion, such as basal cell carcinoma or seborrhoeic keratosis. Some of the curettings are sent for histopathology. These samples are not suitable for determining if a lesion has been completely removed.

Incisional biopsy

Incisional biopsies refer to removal of a larger ellipse of skin for diagnosis, using a scalpel blade. Stitches are usually required after an incisional biopsy.

Excision biopsy

Excision biopsy refers to complete removal of a skin lesion, such as a skin cancer. A margin of surrounding skin is taken, as a precaution. Smaller lesions are most often removed using a scalpel blade as an ellipse, with primary closure using sutures. Larger excisions may be repaired using a skin flap (moving adjacent skin to cover the wound) or graft (skin taken from another site to patch the wound).

Complications of skin biopsy

Skin biopsy is usually straightforward and complications are uncommon.

Bleeding

Intraoperative or postoperative bleeding can occur in anyone, but can be particularly troublesome in those with a bleeding tendency, or taking blood-thinning medications such as warfarin or aspirin.

Infection

Bacterial wound infection affects about 1–5% of surgeries. It is more likely in ulcerated or crusted skin lesions. The risk of infection is greater than usual in diabetics, elderly patients, and in people taking immunosuppressive medicines.

Delayed healing

Delayed healing is most likely in biopsies taken from the lower legs, especially if the leg is swollen, the arterial or venous circulation is impaired, or there is a skin condition that predisposes to ulceration after skin injury (eg pyoderma gangrenosum).

Nerve injury

The blade may cut a superficial nerve causing pain or numbness. This is most likely to occur where the skin is thin, for example on the face or back of hand.

Scarring

It is usual for a biopsy site to form a permanent scar. Some people form excessive or hypertrophic scars, particularly in certain body sites such as the centre of the chest.

Persistence or recurrence of the skin lesion

Many biopsies are deliberately partial, so that the underlying skin condition remains. In other cases, complete removal is intended but not achieved; in time, the lesion may recur at the same site.

Obtaining the results of the biopsy

It usually takes about one week to obtain the result from the pathology laboratory, but can sometimes take longer if special stains are required. The pathologist describes what is observed under light microscopy in several sections of the biopsy sample, and provides the likely diagnosis. Sometimes it is not possible to make an exact diagnosis on the biopsy sample provided.

Clinicopathological correlation

Skin diseases and conditions can at times be very difficult to diagnose accurately. The various specialists involved may need to consult with each other. This is called clinicopathological correlation (CPC). Larger organisations hold regular multidisciplinary meetings (MDMs) at which clinical information, clinical photographs, and pathology slides are reviewed by a team of experts to determine the best diagnosis and treatment for the patient.

Related information

On DermNet NZ:

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Author: Dr Sonya Havill, Dermatology Registrar, Waikato Hospital, Hamilton, New Zealand 2001. Updated by A/Prof Amanda Oakley, February 2016.



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