Skin biopsy, simple excision

Question 1

What are the different techniques for skin biopsy?

Answer 1

Shave biopsy - suitable if lesion is elevated above the skin
Punch biopsy - ideal for skin biopsy or removing small lesions, often has better cosmetic result than shave biopsy

Question 2

What are the indications for biopsy?

Answer 2

• All suspected neoplastic lesions - BCC and SCC
• All bullous disorders
• To clarify a diagnosis when a limited number of entities are under consideration

Specifically:

• Shave biopsy -where full thickness of the dermis is not required for diagnosis
• Punch biopsy - where sampling of the deep dermis is required

Question 3

How is a shave biopsy done?

Answer 3

• Wheal of anaesthetic is injected under the lesion to allow it to be propped up
• Lesion is stabilised between thumb and forefinger
• Blade on a scalpel is held tangential to skin surface and lesion removed with a forward sweeping stroke going just under and across the lesion
• Bleeding is usually controlled with pressure alone or aluminium chloride 10% in absolute alcohol

Question 4

How is a punch biopsy carried out?

Answer 4

• Raise wheal of local anaesthetic under the lesion
• Note direction of skin tension lines
• Add punch perpendicular to skin and apply constant firm, downward pressure
• “Give” occurs once subcutaneous fat is reached
• Remove the punch and apply downward pressure at sides of wound to pop up the core
• Excise the core at its base with small tissue scissors
• Apply firm pressure to reduce bleeding +/- aluminium chloride 10%
• Apply one or two sutures

Question 5

Name a contraindication to biopsy.

Answer 5

Infection at the site - although sometimes this is still done.

There are no absolute contraindications.

Question 6

What are the complications of biopsy?

Answer 6

• Scarring
• Bleeding
• Infection
• Dehiscence
• Allergy to topical antibiotics

Question 7

When is simple excision preferred over punch/shave biopsy?

Answer 7

• For biopsy of larger or deeper lesions
• Also preferred for pigmented lesions which are suspicious of melanoma - although very small lesions can be sampled with punch biopsy

Question 8

How is a simple excision carried out?

Answer 8

• Parallel to skin tension lines, an ellipse is drawn including a 2-5mm margin of normal skin around the lesion, with the length being x3 the width
• Lesion is excised at the thickness of the subcutaneous tissue - same depth throughout
• Pressure is applied with a gauze
• Close the incision

NB: diamond shaped excisions may be easier to perform for small lesions