Punch biopsy is one of the most widely used dermatologic procedures in primary care medicine. This technique obtains a full-thickness skin specimen for histologic assessment. A properly performed punch biopsy frequently yields useful diagnostic information. The technique is simple, rapid, and generally results in an acceptable final cosmetic appearance at the site.
Punch biopsy is performed with a circular blade known as a trephine, which is attached to a pencil-like handle. The instrument is rotated using downward pressure until the blade penetrates into the subcutaneous fat. A cylindrical core of tissue is then cut free and placed in formalin for transfer to the laboratory. Most 3- or 4-mm punch biopsy sites are closed with a single suture. The 2-mm punch biopsy sites frequently do not require suture closure, and Monsel's solution can be used for hemostasis if the wound is allowed to granulate.
Punch biopsy is generally performed to evaluate lesions of uncertain origin or to confirm or exclude the presence of malignancy. This biopsy technique is considered the method of choice for many flat lesions. Suspected melanomas can be evaluated by this technique, especially when the lesion is too large for easy removal. The yield may be improved if the most suspicious or abnormal-appearing area (darkest, most raised, or most irregular contour) is biopsied. If the suspicion for melanoma is high, it is preferable to perform excisional biopsy to have the entire lesion available for evaluation. Physicians should not fear performing punch biopsy on a melanoma, because the biopsy does not alter the natural course of the disease, and a prompt biopsy expedites definitive treatment.
Punch biopsy used for basal and squamous cell carcinoma has one disadvantage. After these cancers have been biopsied using punch technique, the physician is obligated to perform a definitive excisional technique. Superficial techniques that are frequently employed for these lesions, such as curettage and electrodesiccation, may miss cells that have been driven deeper by the punch instrument.
Physicians should be aware of the underlying anatomy when performing a punch biopsy. Certain areas of the body where there is little subcutaneous tissue pose the greatest threat of damaging underlying structures such as arteries, tendons, or nerves. Punch biopsy on the upper cheek can damage the facial or trigeminal nerves, and punch biopsy of the lateral digits or of the thin eyelids should be approached with great caution.
The punch biopsy instrument (i.e., trephine) has a plastic, pencil-like handle and a circular scalpel blade. The blade attaches to the handle at the hub of the instrument. Select a punch biopsy instrument of sufficient size (i.e., 4 or 5 mm) to obtain adequate tissue for histologic assessment while minimizing the size of the scar (i.e., 3-mm instrument for biopsy on the face.)
(1) The punch biopsy instrument: trephine.
Select the best site for the biopsy. Perform the punch biopsy at the most abnormal-appearing site within the most abnormal-appearing lesion or at the edge of an actively growing lesion. Tumors of the skin should be biopsied in the center of the lesion (Figure 2A), and bullous lesions should be biopsied at the edge (Figure 2B.)
(2) Select the best site for the biopsy.
PITFALL: Do not biopsy lesions that have been traumatized, scratched, or significantly modified. Biopsy of a traumatized lesion rarely provides useful information. Provide the pathologist with information on the age and sex of the patient, current medications, appearance of the lesion, and body location to increase the chance of gaining useful clinical information from the biopsy. Remember that biopsy of nonspecific rashes, particularly in younger individuals, rarely provides additional information that benefits the clinician.
Prepare for the closure of the punch biopsy site when performing the technique. A circular defect is not easily closed, but an oval or elliptical defect approximates well. After the administration of local anesthesia, stretch the skin 90 degrees (i.e., perpendicular) to the lines of least skin tension using the nondominant hand (Figure 3B.) The lines of least skin tension for the arm are circumferential (i.e., perpendicular to the long axis of the arm) (Figure 3A.) After the punch biopsy is performed, relax the nondominant hand, and the circular defect becomes more oval. Close the defect with a single, small-caliber suture such as 5-0 nylon (Figure 3C.)
(3) Prepare for the closure of the punch biopsy site when performing this technique.
Rotate the punch biopsy instrument with downward force when performing the biopsy. Turn the blade around its handle with a back-and-forth motion until the instrument traverses the full thickness of the skin. Be prepared to stop the downward pressure as soon as the instrument penetrates through the skin. When the trephine penetrates the skin into the subcutaneous fat, the operator often notices a “give.”
(4) Rotate the punch biopsy instrument with downward force when performing the biopsy.
PITFALL: Historically, physicians were instructed to insert the instrument up to the hub. With larger punch instruments, the blade must penetrate 3/8 inch of the skin to reach the hub. Going to the hub is appropriate where the skin is thick (e.g., upper back) but can damage underlying structures such as nerves or tendons where the skin and subcutaneous tissue is thin. Do not push the instrument to the hub when performing punch biopsy on the upper cheek or dorsum of the hand.
Cut the specimen free from the subcutaneous fat after the cylindrical cut is made through skin. Lift the specimen with the needle used to anesthetize the skin site, and then cut it free at the base (beneath dermis) using sharp iris scissors.
(5) Cut the specimen free from the subcutaneous fat after the cylindrical cut is made through the skin.
PITFALL: Many pathologists refuse to examine a skin biopsy specimen that has been crushed. Punch biopsy specimens often are crushed when they are elevated using Adson forceps. Elevate the specimen with the anesthesia needle to avoid crush artifact.
INSTRUMENT AND MATERIALS ORDERING
Basic setup for this procedure includes local anesthesia (1 to 3 mL of anesthetic), the punch biopsy instrument, and sharp iris scissors to cut the specimen free. If the specimen cannot be lifted using the anesthesia needle, Adson pickups without teeth can lift the specimen.
Punch biopsy instruments (Fray Products Corporation, Baird Research Park, Amherst, NY) can be obtained through Delasco, Council Bluffs, IA (phone: 1-800-831-6273; http://www.delasco.com).
Suggested suture removal times are listed in Appendix C. A suggested anesthesia tray that can be used for this procedure is listed inAppendix G. Skin preparation recommedations appear in Appendix H.
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