6. Dermatological Surgery

Learning Objectives

• Describe the standard steps of surgical excision and how margin selection differs by lesion type
• Explain why Mohs micrographic surgery achieves higher cure rates than standard excision for certain skin cancers
• Compare shave, punch, and excisional biopsy techniques and identify when each is appropriate
• Recognize the indications and mechanism of cryotherapy for benign and premalignant lesions
• Apply preoperative risk assessment principles, including anticoagulant management, before a dermatologic procedure
• Identify common postoperative complications and the clinical signs that require prompt follow-up

Quick Answer

Dermatological surgery is the set of procedures dermatologists use to remove, biopsy, or reshape skin tissue — ranging from a five-minute shave biopsy to Mohs micrographic surgery with real-time margin mapping. It matters because skin cancer is the most common cancer worldwide, and how a lesion is removed directly affects cure rate, scarring, and function. The core decision in almost every case is matching the technique to the lesion: cryotherapy for a benign actinic keratosis, standard excision with margins for a straightforward basal cell carcinoma, and Mohs surgery for high-risk or cosmetically sensitive tumors where tissue conservation and complete margin control both matter. Understanding this decision logic — not just memorizing procedure lists — is exactly what USMLE and clinical practice both test.

This page is for educational purposes. Always verify with current clinical guidelines.

Biopsy Techniques: Getting the Diagnosis Before You Treat

Before any lesion is excised or destroyed, dermatologists usually need tissue confirmation. The three workhorse biopsy techniques differ in how much tissue they sample and what they can (and cannot) tell you.

Shave biopsy uses a blade to remove the top of a raised lesion, staying within the epidermis and superficial dermis. It's fast, needs no sutures, and is ideal for lesions thought to be confined to the epidermis (like a suspected seborrheic keratosis or superficial basal cell carcinoma). The catch: a shave biopsy cannot assess the deep or peripheral margins, so it is a poor choice whenever melanoma is suspected — a shallow shave can miss the deepest invasive point (Breslow depth), which is the single most important melanoma prognostic factor.

Punch biopsy uses a circular blade (typically 3–6 mm) to remove a full-thickness cylindrical core of skin down to subcutaneous fat. It's the go-to for inflammatory and infiltrative processes (panniculitis, vasculitis, deep fungal infection) because it samples the full dermis. A single suture usually closes the defect.

Excisional biopsy removes the entire lesion, typically with a narrow margin, and is the preferred initial approach for any lesion where melanoma is a real possibility — it gives the pathologist full architecture and an accurate Breslow depth in one pass, rather than sampling error from a partial biopsy.

Why it matters: choosing the wrong biopsy type for a pigmented lesion is a recurring exam trap. A shave biopsy through a suspected melanoma can transect the base and give a falsely shallow depth, understaging the tumor and undertreating the patient.

Excision: The Default Surgical Procedure

Standard surgical excision removes the visible lesion plus a margin of clinically normal-appearing tissue, based on the presumed or confirmed diagnosis.

Procedure steps:

1. Mark the lesion and planned margin before injecting anesthetic (swelling distorts borders afterward)
2. Infiltrate local anesthesia (typically lidocaine with epinephrine, unless the site is a digit, nose tip, ear, or penis, where epinephrine is traditionally avoided)
3. Excise the lesion as a fusiform (ellipse) shape oriented along skin tension lines to minimize tension and scarring
4. Send the specimen for histopathology to confirm margins are clear
5. Close in layers if the defect is deep, then close the skin surface

Margins are not arbitrary — they are diagnosis-driven:

• Basal cell carcinoma (low-risk, well-defined): 4 mm margin
• Squamous cell carcinoma (low-risk): 4–6 mm margin
• Melanoma in situ: 5–10 mm margin
• Invasive melanoma: margin scales with Breslow depth — 1 cm for tumors ≤1 mm thick, up to 2 cm for tumors >2 mm thick

This margin-by-depth rule for melanoma is one of the most frequently tested facts in dermatologic surgery, because it links a measurable pathology finding (Breslow depth) directly to a surgical decision.

Mohs Micrographic Surgery: Complete Margin Control

Mohs surgery solves a problem standard excision cannot: conventional "bread-loaf" histology only examines a fraction (often under 1%) of the surgical margin, so a positive margin can be missed. Mohs surgery examines nearly 100% of the peripheral and deep margin in real time, layer by layer, while the patient waits.

How it works:

1. The visible tumor is removed with a thin margin
2. The tissue is mapped, frozen, sectioned horizontally, and stained on-site
3. The Mohs surgeon examines the entire margin under the microscope personally
4. If tumor persists at a specific mapped location, only that area is re-excised — not the whole wound
5. Steps 2–4 repeat until margins are completely clear, then the defect is reconstructed

Why it achieves higher cure rates: because margin assessment is exhaustive rather than sampled, Mohs achieves cure rates up to 99% for primary basal cell carcinoma, compared to roughly 90–95% for standard excision. It also spares the maximum amount of healthy tissue, which is why it is preferred for cosmetically sensitive or recurrent tumors.

Best indications: basal cell carcinoma and squamous cell carcinoma in high-risk locations (nose, eyelids, lips, ears, fingers, genitalia), recurrent tumors, tumors with aggressive histologic subtypes, and lesions with poorly defined clinical borders. Mohs is generally not the primary technique for melanoma, where wide local excision with defined margins (and sentinel lymph node biopsy when indicated) remains standard, though some centers use modified Mohs protocols with immunostains for melanoma in situ.

Cryotherapy: Destruction Without Excision

Cryotherapy uses liquid nitrogen (around -196°C) to freeze and destroy tissue, causing intracellular ice crystal formation, cell membrane rupture, and vascular stasis in the treated area. Because it destroys tissue rather than removing it, no specimen is sent for histopathology — which means cryotherapy is only appropriate when the diagnosis is already clinically certain and benign or premalignant.

Common indications: actinic keratoses, warts (verrucae), seborrheic keratoses, and some superficial basal cell carcinomas in select low-risk cases.

Why it's not used for suspicious pigmented lesions: freezing destroys the tissue architecture, so if the lesion turns out to be melanoma or another malignancy requiring staging, the opportunity for accurate histologic diagnosis is lost permanently. This is the key contraindication to remember.

Other Common Procedures

Liposuction removes excess subcutaneous fat through cannula suction; it is cosmetic rather than oncologic, and complications include contour irregularity, seroma, and (rarely) fat embolism.

Chemical peels use controlled chemical injury to resurface skin. Depth of penetration determines both effect and risk: light peels (glycolic or lactic acid) affect only the epidermis with minimal downtime; medium peels (trichloroacetic acid) reach the papillary dermis and treat photoaging and fine wrinkles; deep peels (phenol) reach the reticular dermis, give the most dramatic results, but carry real risks of scarring, permanent pigment change, and — because phenol is cardiotoxic when absorbed systemically — cardiac arrhythmia during the procedure, so cardiac monitoring is required.

Decision Pathway: Choosing the Right Technique

Perioperative Care

Preoperative: review anticoagulant and antiplatelet use with the prescriber before stopping anything — most dermatologic procedures actually proceed safely on aspirin or warfarin because the bleeding risk of stopping (stroke, MI, clot) usually outweighs the surgical bleeding risk. Also confirm smoking status (impairs flap and graft healing), allergy history (especially to lidocaine or latex), and obtain informed consent covering scarring and recurrence risk.

Intraoperative: maintain sterile technique, use epinephrine-containing anesthetic to reduce bleeding except at end-organ sites (digits, nose, ears, penis) per the traditional teaching, and mark margins before the tissue swells or distorts.

Postoperative: keep the wound covered and moist (moist wound healing reduces infection and improves cosmesis), watch for the classic infection triad of increasing pain, spreading erythema, and purulent drainage typically after 48–72 hours, and schedule suture removal timed to site — 5–7 days on the face, 10–14 days on the trunk or extremities, where tension is higher.

Complications and Risks

• Common: infection, bleeding/hematoma, hypertrophic or keloid scarring, transient nerve irritation
• Site-specific nerve injury: temporal branch of the facial nerve (forehead lifts brow, injury causes brow ptosis), marginal mandibular branch (lower lip), and spinal accessory nerve (posterior neck/shoulder, injury causes shoulder drop) are classic exam points because they occur near common excision sites
• Serious but less common: tumor recurrence at the margin, lymphedema after lymph node dissection for melanoma staging, and systemic toxicity from local anesthetics (perioral numbness and tinnitus progressing to seizures at high doses — lidocaine toxicity)

Key Terms

Term	Definition	Related Concept
Mohs micrographic surgery	Staged excision with complete margin examination under the microscope during the procedure	Basal cell carcinoma, squamous cell carcinoma
Breslow depth	Measured thickness of a melanoma from the granular layer to the deepest invasive cell	Melanoma margin selection, prognosis
Shave biopsy	Superficial removal of a lesion with a blade, sampling epidermis and superficial dermis only	Contraindicated for suspected melanoma
Punch biopsy	Full-thickness cylindrical tissue sample using a circular blade	Inflammatory and infiltrative skin disease
Excisional biopsy	Complete removal of a lesion with a margin, sent for histopathology	Preferred for suspected melanoma
Cryotherapy	Tissue destruction using liquid nitrogen without histologic specimen	Actinic keratosis, warts
Fusiform excision	Elliptical excision shape oriented along skin tension lines	Minimizing scar tension
Sentinel lymph node biopsy	Removal of the first draining lymph node to assess micrometastasis	Melanoma staging
Hypertrophic scar	Raised scar confined to the wound margin	Postoperative complication
Keloid	Scar tissue that grows beyond the original wound margin	Genetic predisposition, higher risk in darker skin
Trichloroacetic acid (TCA)	Medium-depth chemical peel agent reaching the papillary dermis	Photoaging treatment
Lidocaine toxicity	Systemic anesthetic toxicity causing perioral numbness, tinnitus, and seizures at high dose	Local anesthesia safety

Common Mistakes

Misconception: A shave biopsy is always an acceptable way to sample a pigmented lesion. Why it's wrong: A shave biopsy only captures superficial tissue. If the lesion is actually a melanoma, the blade can transect the tumor base, making it impossible to measure the true Breslow depth — the single most important factor for staging and margin planning. Correct understanding: Any lesion with real melanoma suspicion should undergo excisional (or at minimum deep saucerization/punch) biopsy so the full depth is captured in one specimen.

Misconception: Patients on aspirin or warfarin should always stop their blood thinner before dermatologic surgery to prevent bleeding. Why it's wrong: For most minor dermatologic procedures, the risk of a thromboembolic event (stroke, MI, valve thrombosis) from stopping anticoagulation outweighs the modest, usually manageable increase in surgical bleeding. Correct understanding: Current dermatologic surgery guidance is to continue aspirin and warfarin for routine excisions and Mohs surgery, and to have the prescribing physician weigh in before any change.

Misconception: Cryotherapy is a reasonable option whenever a lesion "looks benign" but you're not entirely sure. Why it's wrong: Cryotherapy destroys the tissue on contact, so no histologic diagnosis is possible afterward. If the lesion turns out to be malignant, that diagnostic opportunity is gone and the true extent of disease is unknown. Correct understanding: Cryotherapy should only be used when the clinical diagnosis is already confidently benign or premalignant (actinic keratosis, common wart, seborrheic keratosis) — any diagnostic uncertainty warrants biopsy first.

Comparison and Connections

Feature	Standard Excision	Mohs Micrographic Surgery	Cryotherapy
Margin assessment	Sampled (bread-loaf sections)	Complete (near 100% of margin)	None — no specimen
Tissue conservation	Moderate	Highest	Not applicable (destructive)
Best indications	Low-risk BCC/SCC, straightforward melanoma excision	High-risk site, recurrent or aggressive BCC/SCC	Actinic keratosis, warts
Cure rate (BCC)	~90–95%	Up to 99%	Lower, variable
Histologic diagnosis obtained	Yes	Yes	No
Typical setting	Same-day, single stage	Same-day, multi-stage (hours)	Same-day, single visit

Practice Questions

Recall

1. What temperature does liquid nitrogen reach during cryotherapy, and what cellular mechanism destroys the tissue? Answer guidance: Approximately -196°C; ice crystal formation ruptures cell membranes and causes vascular stasis leading to tissue necrosis.

2. List the three main biopsy techniques used in dermatology. Answer guidance: Shave biopsy, punch biopsy, and excisional biopsy.

Understanding

3. Why does Mohs micrographic surgery achieve a higher cure rate than standard excision for basal cell carcinoma? Answer guidance: Standard excision histology examines only a sampled fraction of the margin, so a small focus of residual tumor can be missed. Mohs examines nearly the complete peripheral and deep margin in real time, so residual tumor is far less likely to be left behind.

4. Why is excisional margin size for melanoma tied to Breslow depth rather than a fixed number? Answer guidance: Thicker melanomas have a higher risk of local microsatellite spread and recurrence, so wider margins (up to 2 cm for tumors over 2 mm thick) are needed to capture occult extension, while thin melanomas need only 1 cm to achieve the same safety margin without excess morbidity.

Application

5. A 70-year-old man on warfarin for atrial fibrillation needs an excisional biopsy of a suspicious lesion on his forearm. Should his warfarin be stopped? Answer guidance: Generally no. Current dermatologic surgery practice continues warfarin for most excisions because the risk of a thromboembolic event outweighs the surgical bleeding risk, which can usually be managed with local hemostatic measures. Confirm with the prescribing physician if there is any uncertainty.

6. A patient has a 6 mm nodule on the nasal tip that biopsy confirms is basal cell carcinoma with an infiltrative growth pattern. What surgical approach is most appropriate and why? Answer guidance: Mohs micrographic surgery, because the nose is a high-risk, cosmetically sensitive site with limited tissue to spare, and infiltrative BCC has poorly defined clinical margins that standard excision is more likely to miss.

Analysis

7. Compare what would happen if a suspected melanoma were sampled with a shave biopsy versus an excisional biopsy, in terms of staging accuracy. Answer guidance: A shave biopsy risks transecting the base of the lesion, understating the true Breslow depth and potentially leading to inadequate margins and understaged, undertreated disease. An excisional biopsy captures the full lesion depth in one specimen, giving an accurate Breslow depth that correctly guides margin width and the decision for sentinel lymph node biopsy.

8. A patient develops a red, tender, draining wound five days after excisional surgery. Separately, another patient notices their scar becoming raised and extending beyond the original incision months later. How do these two complications differ in cause and management? Answer guidance: The first describes wound infection — an acute process from bacterial contamination, managed with wound care and antibiotics. The second describes a keloid — a delayed fibroproliferative scarring response related to genetic predisposition (more common in darker skin types), managed with intralesional corticosteroids, pressure therapy, or laser rather than antibiotics.

FAQ

Q: Why doesn't every skin cancer get treated with Mohs surgery if it has the highest cure rate? Mohs surgery is time- and resource-intensive — it requires a specially trained Mohs surgeon, an on-site histology lab, and the patient often waits hours while margins are processed in stages. For a low-risk, well-defined basal cell carcinoma on the trunk, standard excision already achieves a very good cure rate at a fraction of the cost and time. Mohs is reserved for situations where its extra precision meaningfully changes the outcome: high-risk anatomic sites, recurrent tumors, and aggressive histologic subtypes.

Q: If cryotherapy doesn't give a tissue diagnosis, how do dermatologists know it's safe to use? They rely on a confident clinical diagnosis based on visual and sometimes dermoscopic examination. Lesions like common warts, seborrheic keratoses, and actinic keratoses have characteristic, well-recognized appearances. If a lesion looks atypical, has ABCDE features, or the diagnosis is at all in doubt, biopsy is performed first rather than treating blind with cryotherapy.

Q: What's the actual difference between a scar that heals well and a keloid? A normal scar stays confined within the boundaries of the original wound and gradually flattens and fades over months. A hypertrophic scar is raised but still confined to the wound. A keloid grows beyond the original wound margins entirely, can continue growing for years, and is more common in darker-skinned patients and on the chest, shoulders, and earlobes. Keloids do not resolve on their own and typically need intralesional steroid injections or other targeted treatment.

Q: Why is epinephrine avoided in local anesthesia for fingers, toes, nose, ears, and penis? The traditional teaching is that these are areas with end-arterial blood supply and limited collateral circulation, so epinephrine-induced vasoconstriction could theoretically cause ischemia. More recent evidence suggests epinephrine is actually safe in digits at appropriate doses, but many training programs and exam questions still test the classic "no epinephrine in digits" rule, so it's worth knowing both the traditional teaching and the modern nuance.

Q: How soon after dermatologic surgery can a patient expect sutures to come out? It depends on the tension and cosmetic priority of the site. Facial sutures are typically removed at 5–7 days, since the face heals quickly and prolonged suture presence risks visible track marks. Sutures on the trunk, back, or extremities, where wound tension is higher and healing slower, stay in longer — typically 10–14 days — to avoid the wound reopening (dehiscence).

Quick Revision

• Shave biopsy samples only superficial tissue; never use it when melanoma is suspected because it can transect the tumor base and understate Breslow depth
• Excisional biopsy is preferred for suspected melanoma because it captures full-thickness architecture and accurate depth
• Melanoma excision margins scale with Breslow depth: 1 cm for ≤1 mm thick tumors, up to 2 cm for >2 mm thick tumors
• Standard BCC/SCC excision margin is typically 4–6 mm for low-risk lesions
• Mohs micrographic surgery examines nearly 100% of the margin in real time and achieves cure rates up to 99% for BCC
• Mohs is reserved for high-risk sites (face, nose, ears, digits, genitalia), recurrent tumors, and aggressive histologic subtypes
• Cryotherapy destroys tissue with liquid nitrogen and gives no histologic specimen — use only when diagnosis is clinically certain
• Most patients should continue aspirin and warfarin through routine dermatologic surgery; stopping raises thromboembolic risk
• Facial nerve branches (temporal, marginal mandibular) and the spinal accessory nerve are classic injury sites during excision near the face and neck
• Deep chemical peels using phenol carry cardiotoxicity risk and require cardiac monitoring during the procedure
• Keloids extend beyond the original wound and are more common in darker skin; hypertrophic scars stay within the wound border
• Signs of postoperative infection (increasing pain, spreading erythema, purulent drainage) typically appear 48–72 hours after the procedure

Related Topics

Prerequisites: Skin structure and layers (epidermis, dermis, hypodermis), basic skin cancer types (basal cell carcinoma, squamous cell carcinoma, melanoma), local anesthetic pharmacology

Related Topics: Oncology (staging and sentinel lymph node biopsy principles), Pharmacology (local anesthetic toxicity, anticoagulant management), Wound Care (moist wound healing, scar management)

Next Topics: Skin Cancer and Precancerous Lesions, Melasma and Pigmentary Disorders, Cosmetic Dermatology Procedures