Biopsy & Excision Techniques

The punch biopsy is a full-thickness sampling technique that obtains a cylindrical core of tissue through the epidermis, dermis, and into the subcutaneous fat. The circular blade is rotated with gentle downward pressure while the skin is stretched perpendicular to the relaxed skin tension lines (RSTLs). This creates an elliptical wound that can be closed with a single suture. Technique: prep and anesthetize the site, stretch the skin perpendicular to RSTLs, rotate the punch with steady downward pressure until loss of resistance (indicating entry into the subcutis), remove the punch, gently elevate the specimen with forceps (avoid crush artifact), and transect the base with scissors. Close with a single suture or allow secondary intention healing for ≤3mm punches.

Shave biopsy removes a disc of tissue from the epidermis and superficial to mid-dermis using a tangential cutting motion. Techniques range from superficial shave (razor blade/DermaBlade) to deep saucerization (scoop shave) that extends into the reticular dermis. Technique: raise a wheal of local anesthetic beneath the lesion to create a platform, stabilize the skin with the non-dominant hand, and use a DermaBlade, flexible razor blade, or #15 blade held parallel to the skin surface. The blade is drawn across with a smooth, sawing motion. For saucerization, angle the blade slightly downward to capture deeper tissue. Hemostasis is achieved with aluminum chloride 20% (Drysol) or electrodesiccation.

Incisional biopsy removes a representative wedge or ellipse of tissue from a larger lesion, sampling through the full depth of the dermis and into the subcutis. It is indicated when the clinical differential includes entities requiring deep tissue sampling (panniculitis, deep fungal infection, morphea) or when the lesion is too large for complete excisional biopsy. Technique: orient the incision to facilitate future definitive excision. Include both abnormal and adjacent normal tissue at the lesion border. Ensure the biopsy extends to the subcutis for adequate depth. Close in layers.

The fusiform excision is designed as an elongated ellipse with pointed tips at 30-degree angles. The standard 3:1 length-to-width ratio ensures that the wound can be closed without standing cutaneous deformities (dog ears) at the tips. Shorter ratios (2:1) create dog ears; longer ratios (4:1) remove excess tissue unnecessarily. Alignment: the long axis should be parallel to the RSTLs whenever possible. On the face, this typically follows expression lines. Margin marking: use a ruler to mark the desired clinical margin around the tumor, then design the ellipse around the marked margin. Never let the ellipse shape compromise the margin width.

Excision begins with scoring the planned ellipse with the #15 blade tip to create a visible guideline. The incision is then carried through with the blade held perpendicular to the skin surface along the lateral margins, transitioning to a 30-degree angle at the tips to create the pointed ends. The tissue is elevated from one tip using skin hooks (never crush the specimen with toothed forceps), and the subcutis is incised with the blade angled slightly inward. Undermining: performed in the subcutaneous fat (above the fascia) using blunt dissection with scissors or sharp dissection with the blade. Undermine 1–2cm beyond each wound edge to reduce closure tension. On the face, undermine in a plane superficial to the muscular aponeurotic layer. Hemostasis with electrocautery before closure.

Standing cutaneous deformities (dog ears) are mounds of redundant tissue at the tips of an elliptical closure. They occur when the length-to-width ratio is insufficient or when wound edges have unequal lengths. Standard repair technique: extend the incision beyond the dog ear in the direction of the planned scar line. Hook or elevate the redundant tissue mound, incise one side at a 45–60-degree angle to create a triangular excision, then trim the opposite side to match. M-plasty: an alternative that shortens the overall scar by converting each tip into a small M shape. Useful when the standard ellipse would cross an anatomic landmark (eyebrow, hairline, vermilion border). Rule of thumb: small dog ears in thick skin (scalp, back) often flatten with time and wound maturation. Observe for 3–6 months before revising.

The standard protocol involves 2–3 cycles of curettage followed by electrodesiccation: Cycle 1: Curette the visible tumor using firm, systematic strokes in multiple directions. The curette catches on and scoops out the soft tumor tissue until the firm, gritty texture of normal dermis is felt throughout the base and edges. Apply electrodesiccation to the curetted base to char a 1mm layer. Cycle 2–3: Repeat curettage of the charred tissue and an additional 2–3mm margin of surrounding normal skin. The wound heals by secondary intention over 4–8 weeks.

C&E achieves cure rates of 92–97% for appropriately selected tumors but drops to 50–80% when used for inappropriate indications. Strict patient selection is critical.