Summary

Skin biopsy is a fundamental diagnostic procedure in dermatology and primary care, used to obtain tissue for histopathological analysis. The choice of technique (Shave, Punch, or Excision) depends on the suspected pathology, lesion depth, anatomical location, and cosmetic concern. Correct technique selection is critical: a shave biopsy on a suspected melanoma is a serious error as it destroys the Breslow depth, preventing accurate staging. This guide covers indications, technique, post-procedure care, and common pitfalls.

Key Facts

• Shave Biopsy: Superficial sampling. Best for pedunculated or raised benign lesions (SK, Warts). Leaves flat, hypopigmented scar.
• Punch Biopsy: Full-thickness core (2-8mm). Gold standard for inflammatory dermatoses and rashes. Needs 1-2 sutures.
• Excision Biopsy: Removes entire lesion with margin. Required for suspected melanoma (Breslow staging). Ellipse (3:1 Length:Width).
• Contraindication: NEVER shave a pigmented lesion you cannot confidently diagnose.
• Local Anaesthetic: Lidocaine 1-2% +/- Adrenaline. Ring block or local infiltration.

Clinical Pearls

The "Melanoma Rule": If in doubt about a pigmented lesion, always excise in full. A shave biopsy that transects a melanoma is a medico-legal issue. You lose the depth information (Breslow) needed for staging.

The "SCC Rule": For suspected SCC on sun-damaged skin, a deep shave (saucerization) or punch is fine to diagnose, but definitive excision with margin must follow if positive.

Adrenaline Myth: The old teaching to avoid adrenaline in fingers/toes is largely debunked. It is safe in most cases and dramatically reduces bleeding.

Why This Matters Clinically

Skin biopsy is one of the most commonly performed procedures in medicine. A poorly chosen technique can delay diagnosis, cause cosmetic disfigurement, or destroy staging information for skin cancer. Every clinician performing minor surgery should master these skills.

Relaxed Skin Tension Lines (RSTL / Langer's Lines)

The key to minimal scarring.

• RSTL run parallel to underlying muscle fibres.
• On the face, they follow natural creases (crow's feet, nasolabial fold).
• Ellipse orientation: Always align the long axis of your ellipse ALONG the RSTL.
• Result: Scar falls into a natural crease and becomes invisible.

Danger Zones (Anatomical Hazards)

Local Anaesthetic Pharmacology

Adrenaline Benefits:

1. Vasoconstriction -> Bloodless field.
2. Delays absorption -> Longer duration.
3. Reduces systemic toxicity.

When to Biopsy

Quality Markers: What Makes a "Good" Biopsy?

For audit and training.

Standard Minor Surgery Trolley

Anticoagulation Management

A common source of pre-procedure anxiety.

Haemostasis Tips for Anticoagulated Patients:

• Use Adrenaline-containing LA.
• Cautery (Bipolar or Silver Nitrate).
• Pressure dressing. Elevate limb if on leg.
• Absorbable deep sutures to close dead space.

Training & Competency

What should a Foundation Doctor (FY1/FY2) be able to do?

Indication

• Raised benign lesions (Seborrhoeic Keratosis, Skin Tags, Intradermal Naevi, Papillomas).
• NOT for: Suspected Melanoma, Deep lesions.

Procedure

1. Consent: Explain scar, infection, bleeding, incomplete excision.
2. Clean: Chlorhexidine. Mark if needed.
3. Anaesthetise: Infiltrate under the lesion. Use adrenaline-containing LA to raise a "bleb".
4. Technique:
   • Hold blade parallel to skin surface (or slightly tilted).
   • With a gentle sawing motion, slice through the base of the raised lesion.
   • For deeper lesions (e.g., BCC), a "Saucerization" technique scoops deeper.
5. Haemostasis: Aluminium Chloride (Monsel's Solution) or Electrocautery.
6. Specimen: Place in Formalin pot immediately.
7. Dressing: Non-adherent dressing (Mepitel/Allevyn). Heals by secondary intention.

Drill Down: Saucerization

For deeper sampling without ellipse.

• Tilt the blade to ~45 degrees and scoop out a "dish" of tissue.
• Allows sampling of mid-dermis.
• Use for suspected BCC or superficial SCC (but not melanoma).

Indication

• Inflammatory skin disease (Psoriasis, Eczema, Lichen Planus, Vasculitis).
• Diagnosis of rash of unknown origin.
• Bullous disease (perilesional sample for IMF).
• Small pigmented lesions (if 2mm punch can fully excise).

Size Selection

Procedure

1. Consent: Explain scar (small round), infection, bleeding.
2. Clean & Mark: Choose representative lesion area.
3. Anaesthetise: Raise bleb under lesion. Don't distort.
4. Stretch Skin: Stretch skin perpendicular to relaxed skin tension lines (RSTL). This makes the eventual wound elliptical, closing better.
5. Punch: Apply downward pressure and rotate punch in one direction (to avoid tangling dermis). Twist until you feel "give" (into subcutis).
6. Remove Core: Lift gently with toothed forceps (don't crush). Snip base with scissors.
7. Haemostasis: Pressure or Cautery.
8. Closure: Single interrupted suture (or Steri-Strip if small). If letting heal by secondary intention, use Alginate.
9. Specimen: Formalin (or Michel medium for DIF).

Drill Down: The "One Direction" Twist

• Twisting the punch back and forth shreds collagen fibres -> Poorer histology.
• Twist consistently in ONE direction (like a corkscrew).

Indication

• Melanoma: Gold standard. Requires 2mm clinical margin (narrow excision) for diagnosis. Wide local excision follows later based on Breslow.
• Complete removal of benign lesions (Lipoma, Cyst, Large Naevus).
• Suspected malignancy where depth matters.

Margin Guidance (Initial Diagnostic Excision)

Ellipse Design

• Orientation: Long axis follows Relaxed Skin Tension Lines (RSTL/Langer's Lines). See wrinkle lines on face.
• Ratio: Length : Width = 3:1 (or 4:1 on tight skin). Prevents "dog ears".
• Margin: Mark margin around lesion before incision.

Procedure

1. Consent: Explain scar, infection, bleeding, need for wider excision if melanoma.
2. Clean & Mark: Draw ellipse with sterile pen. Include margin.
3. Anaesthetise: Field block around the ellipse. Avoid injecting into the lesion.
4. Incise: Cut vertically through skin along marked lines. Scalpel held perpendicular.
5. Undermine: Use scissors or scalpel to dissect specimen from subcutis.
6. Haemostasis: Cautery or diathermy.
7. Orientate Specimen: Place suture at 12 o'clock for pathologist orientation (if needed).
8. Closure: Layered closure (Deep Vicryl + Superficial Nylon/Prolene). Evert edges.
9. Dressing: Steri-strips + Non-adherent dressing.

Drill Down: Dog Ears

The bunched-up skin at ellipse ends.

• Caused by too wide or too short an ellipse.
• Correction: Extend ellipse. Or "Burow's Triangle" excision at each end.

Instructions After Your Skin Biopsy

For the first 24-48 hours:

• Keep the dressing dry.
• Take Paracetamol if sore. Avoid Ibuprofen (may increase bleeding).

After 48 hours:

• You can gently shower. Pat dry.
• Keep wound covered with a clean dressing until sutures out.

Suture Removal:

• Face: 5-7 days.
• Scalp/Body: 7-10 days.
• Back/Legs/Feet: 10-14 days.

When to call:

• Increasing redness or swelling around the wound.
• Pus or discharge.
• Fever.
• Bleeding that doesn't stop with 10 mins pressure.

Bullous Disease Biopsy (Pemphigoid / Pemphigus)

• Why different?: Need to look for antibodies stuck to skin (Direct Immunofluorescence - DIF).
• Technique: Take TWO punches:
  1. One from lesional skin (blister edge) -> Formalin (H&E).
  2. One from perilesional, non-blistered skin -> Michel's Transport Medium (NOT Formalin). This is for DIF.

Vasculitis Biopsy

• Need deep tissue to see blood vessel walls.
• Use large punch (4-6mm) or small incisional biopsy.
• Sample fresh lesion (<48 hours old). Old lesions lose diagnostic features.

Melanoma-in-Situ (Lentigo Maligna)

• The edges can be ill-defined on sun-damaged skin.
• Multiple Scouting Punches may be taken around the clinical edge to map the true extent before definitive surgery.

Key Guidelines

Evidence Strength

Understanding the Histopathology Report

Common Histology Patterns

"The Shaved Melanoma"

• Scenario: GP shaves a "benign-looking" mole. Histology shows Melanoma. Breslow depth cannot be accurately staged (Transected at base).
• Problem: Patient requires sentinel lymph node biopsy and wide local excision, but staging is now uncertain. Prognosis affected. Litigation risk high.
• Lesson: If you cannot confidently diagnose a pigmented lesion as benign, excise it completely or refer.

"The Crushed Punch"

• Scenario: Forceps crush the biopsy specimen during removal. Histology is uninterpretable.
• Lesson: Use toothed forceps gently at the edge. Never squeeze the diagnostic tissue.

"The Wrong Pot"

• Scenario: Specimen for Direct Immunofluorescence (DIF) placed in Formalin instead of Michel's Medium. Antibodies destroyed.
• Lesson: Formalin for H&E. Michel's/Saline for DIF. Write clearly on pots.

"The Inadequate History"

• Scenario: Histopathologist receives a pot labelled "? Skin lesion. Query diagnosis."
• Lesson: Provide Site, Duration, Size, Description, Clinical Differential. The pathologist is not a mind reader.

Key Consent Points

1. Explain Purpose: "We are taking a small sample of skin to examine under a microscope to find out what is causing your [lesion/rash]."
2. Explain Pain: "You will feel a sharp scratch and some pressure."
3. Explain Risks: Bleeding, Infection, Scar, Incomplete sampling (may need repeat), Keloid (if relevant).
4. Explain Alternatives: "We could wait and watch, but a biopsy gives us more information."
5. Document: Record consent discussion in notes.

Sample Documentation (Clinical Notes)

Procedure: 4mm Punch Biopsy L shin
Indication: Persistent rash, ? Lichen Planus
Consent: Verbal consent obtained. Risks (bleeding, infection, scar) explained. Patient understands.
Anaesthetic: 1mL 2% Lidocaine + Adrenaline infiltrated locally.
Procedure: Skin prepped with Chlorhexidine. 4mm punch biopsy performed. Core removed intact with no crush artefact. Haemostasis achieved with pressure. Closed with single 4-0 Nylon interrupted suture.
Specimen: Sent to Histopathology in Formalin.
Post-op: Wound care advice given. Review with results in 2 weeks.
Signed: Dr X, Date.

Procedural Success

• Punch Biopsy: Diagnostic yield >95% if correctly selected lesion and adequate depth.
• Shave Biopsy: Excellent for benign superficial lesions. ~10% may need repeat if shaved too shallow.
• Excision Biopsy: Gold standard for oncological diagnosis.

Healing Time

Exam Scenarios (Common Vivas)

Scenario 1:

• Stem: 45yo woman with a 6mm pigmented lesion on her back. Dermoscopy shows irregular network. What biopsy?
• Answer: Excision Biopsy with 2mm clinical margin. Shave is contraindicated.

Scenario 2:

• Stem: 70yo man with a persistent scaly red plaque on his face, present for 2 years. ?Bowen's or ?SCC. What biopsy?
• Answer: Punch Biopsy (4mm) or Deep Shave (Saucerization) to confirm invasive vs. in-situ.

Scenario 3:

• Stem: 25yo woman with itchy, scaly plaques on elbows and knees. Clinical diagnosis is psoriasis. Why biopsy?
• Answer: You might NOT need to biopsy if clinically classic. If atypical, a 4mm punch from the margin confirms histological pattern.

Scenario 4:

• Stem: A 65yo presents with tense blisters. You suspect Bullous Pemphigoid. How many biopsies and where?
• Answer: TWO biopsies. One from blister edge for H&E (Formalin). One from perilesional UNINVOLVED skin for DIF (Michel's Medium).

Scenario 5:

• Stem: FY2 doctor takes a punch biopsy but the path report says "Crush artefact. Uninterpretable."
• Answer: The specimen was damaged by forceps. Repeat biopsy using toothed forceps gently from the edge, not crushing the core.

Scenario 6:

• Stem: Patient on Warfarin (INR 2.8) needs a punch biopsy. What do you do?
• Answer: PROCEED. INR <3.5 is acceptable for minor skin surgery. Use Adrenaline LA, cautery, and pressure dressing.

What is a skin biopsy?

A skin biopsy is a simple procedure where a small sample of your skin is taken to be looked at under a microscope. This helps doctors find out what is causing a rash or lump.

Does it hurt?

You will have an injection of local anaesthetic (the same kind dentists use), which stings briefly. After that, the area goes numb and you should feel no pain.

Will it leave a scar?

There will be a small scar. The size depends on the type of biopsy. Most heal very well and fade over time.

How long does it take?

About 5-15 minutes. You can go home immediately.

When do I get the results?

Usually 1-2 weeks. Your GP or specialist will contact you.