Surgical and Procedural Dermatology: Biopsy, Margins and Closure
Surgical and Procedural Dermatology tests procedural judgement rather than operative speed: which biopsy answers the question, what margin is adequate, how to anaesthetise safely, and when to refer for Mohs or reconstruction.
Core rules
- Choose the biopsy that answers the question. Inflammatory disease: 4 mm punch or deep incisional biopsy including subcutaneous fat; suspected melanoma: full-thickness excisional biopsy with 1–2 mm clinical margins and orientation; suspected deep infection or panniculitis: incisional or excisional biopsy, not superficial swab.
- Excision margins follow diagnosis and site. Benign lesions: complete removal with minimal margin. Melanoma: Breslow-based margins (in situ 0.5–1 cm; ≤1 mm 1 cm; 1–2 mm 1–2 cm; >2 mm 2 cm) after diagnostic biopsy. BCC: 3–4 mm for low-risk nodular lesions; SCC: 4–6 mm; adjust for high-risk features, immunosuppression and facial sites.
- Anaesthesia: calculate maximum lidocaine dose (4.5 mg/kg plain; 7 mg/kg with adrenaline) and use adrenaline cautiously on digits, nose and ears. Buffering reduces injection pain.
- Hemostasis: direct pressure, electrocautery, absorbable gelatin sponge; reverse anticoagulation only after cardiology advice.
- Closure: undermine, approximate without tension, evert wound edges; use non-absorbable skin sutures on face 5–0/6–0, trunk 3–0/4–0. Remove facial sutures at 5–7 days, trunk at 10–14 days.
- Mohs is tissue-sparing for high-risk BCC/SCC and some melanoma in situ; cryotherapy is for superficial, well-demarcated benign lesions, not suspected melanoma.
Worked example
A 45-year-old man has a 7 mm irregular pigmented macule on the upper back. Do not shave or laser it. Perform an excisional biopsy with 2 mm margins, orient with a suture, and send for histology. If melanoma is confirmed, re-excise to Breslow-appropriate margins and stage.
Traps
Shave biopsy of suspected melanoma distorts Breslow depth. Do not use adrenaline in a digital block without caution. Do not close a contaminated wound primarily. Document site, orientation, specimen laterality and suture type.