A punch biopsy is a type of skin biopsy. It is a diagnostic procedure that punches a hole in the skin to acquire tissue for laboratory examination, usually through microscopy or tissue culture. Skin biopsies, compared with biopsies of other organs, are relatively low-risk procedures that are conducted under local anesthesia, with very few associated complications. Punch biopsy is one of the three main types of skin biopsies. The other two are shave and excisional biopsies.
In punch biopsies, small pieces of skin, from any part of the body, are removed using a tube-shaped sharp cutting tool. This tool has a blade that ranges in size from 1 mm to 8 mm. It is attached to a handle that can be rotated through the layers of skin, namely the dermis and epidermis, into the subcutaneous fat. This motion results in the production of a cylindrical sample. This specimen is then sent to a dermatologist, pathologist or dermato-pathologist, where it undergoes tissue fixation, preparation of slides and staining before microscopic examination. Alternatively, the sample may be stored in a solution for taking bacterial or viral laboratory cultures.
Before conducting the procedure, the affected area is carefully marked, and the age of the lesion must be known. This is crucial, because when biopsies conducted prematurely or too late, may negatively affect results. In contrast to other biopsy methods, punch biopsies tend to heal with smaller scars that are typically smaller than the size of the instrument used. The healing time may be shortened still more if sutures are used to close the thickness of the wound.
Suspicious growths on the skin are the primary indications for a biopsy. The procedure is performed to evaluate the lesions or to confirm the type of malignant growth found. These cancerous growths include melanoma, squamous cell carcinoma and basal cell carcinoma. They are biopsied prior to employing more invasive surgical procedures to treat them.
Cutaneous eruptions which may have multiple etiologies are also indications for a biopsy. Punch biopsies are typically the best type of skin biopsies since they enable examination of the full thickness of the skin. They may be performed in an outpatient setting, in the ward or operating room. Factors to be taken into account while planning the procedure include its psychological aspects and any direct consequences that may be expected from the results and/ or procedure.
In some cases the sample is used to obtain a genetic diagnosis, either by cytogenetic or chromosomal study, and sometimes for the purpose of fibroblast culture.
There are few contraindications for performing a biopsy. These include allergy to local anesthetics and an active infection at the site of planned biopsy. Precautions are necessary in those patients who are on medications that affect the coagulation system, and in those with bleeding disorders. These may increase the risk of bleeding with the procedure if hemostasis is compromised.
Minor complications may occur after the procedure, and should be explained to the patient. Measures to identify and deal with them should be taken. Expected complications include:
- Pain at the biopsy site
- Infection of the wound
- Bleeding at the site
- Scar formation
Reviewed by Dr. Liji Thomas, MD.