Do You Need to Have a Skin Biopsy

Skin biopsy is often required to confirm a clinical diagnosis. It is a simple, easy, and relatively inexpensive procedure. The general rule regarding its use should be: “If any doubt exists, biopsy!” Biopsies can be used for obtaining a sample of a lesion (incisional biopsy) or can be carried out with the intent of completely removing the lesion (excision al biopsy). Surgically, there are three types of biopsy: shave excision, punch excision, or elliptical excision. All three techniques require the use of cutaneous anesthesia.Shave biopsy is carried out by making a horizontal slice through the skin such that the no. 15 scalpel blade just passes below the expected depth of the lesion. This technique is particularly useful for those elevated lesions in which the pathology is presumptively confined to the epidermis or papillary portion of the dermis. Because the skin is not deeply cut, problems with bleeding rarely occur. Likewise, there is little or no postoperative scarring. Unfortunately, if the depth of the pathology is misjudged the lesions may be transected at a level too superficial for satisfactory identification. Hemostasis is easily obtained with chemical cauterants.

A punch biopsy can be carried out almost as quickly and easily as a shave biopsy. This technique is used for lesions in which the histologic changes are expected to extend to the middle or lower portions of the dermis. The punch used for such biopsies can be envisioned as a very small cookie cutter. This instrument is placed perpendicular to the skin, and with downward pressure the punch is twisted with a back and forth rotary motion such that a cylinder of skin is cut. The fingers of the other hand should be used to stabilize of the skin in order to ensure a smooth cut. The skin should be cut completely through to the depth of the subcutaneous layer. The depth of the cut can be judged by removing the punch and observing the central piece of tissue, the skin has been cut entirely through when the central piece of tissue has shrunken away from the sides and appears loose in the hole. At that point the cylinder of skin is gently lifted with forceps (or on the tip of a needle), and the underlying connection to subcutaneous fat is cut with a sharply pointed small scissors. The defect left by the removal of the skin cylinder can either be left open or, preferably, be closed with a single 5-0 suture. If the defect is left open, a small block of dental Gelfoam can be inserted with a pair of forceps. In most instances, a 3- or 4-mm punch will both provide an adequate piece of tissue and leave a suitably small scar.

If it is necessary to remove a piece of tissue larger than 4 mm in diameter, an elliptical excision ought to be performed . Such excisions are also useful when the pathology to be evaluated is expected to extend to the deep dermis or subcutaneous fat. All too often, pathology present at this depth is inadequately sampled when even a large punch is used.

Prior to carrying out an elliptical excision, markings should be placed on the surface of the skin such that the long axis of the identified ellipse lies in a wrinkle line. The length of the ellipse should be 2.5 to 3 times the required width. Once the skin is suitably marked and anesthetized, the incision can be made with a no. 15 (or other similar) scalpel blade. The blade should be held perpendicular to the surface of the skin throughout the cut so that the edges of the cut are not beveled. The cut should extend completely through the dermis; some subcutaneous fat should be visible at the bottom of the piece of skin when it is removed. Hemostasis is rarely a problem. Pressure alone is usually sufficient, but bleeding vessels may be tied off or coagulated if necessary. If the ellipse is large, the edges of the cut should be undermined to reduce suture tension. Most elliptical excisions can be closed with a single layer of 5-0 nonabsorbent suture, but in some instances a subcutaneous layer of absorbable suture material such as Vicryl will be required. Skin surface sutures on the face should be removed within 5 days, but in other areas it may be necessary to leave the sutures in for 7 to 14 days in order to obtain adequate wound strength.

Tissue removed by anyone of the three biopsy techniques should be placed immediately in a 10% formalin solution for transport to the pathology laboratory. The specimen bottle need not be sterile; a urine collection cup will serve well if prepared containers are not easily available.