What is a Punch Biopsy?
A Punch biopsy is a great way to take a sample of a large lesion or unusual skin rash. A surgical instrument called a punch biopsy is used to remove a “core” of skin. Local anaesthetic is injected before the punch instrument is applied.
Punch biopsies vary in diameter from 2mm to 8mm. A 2mm is suitable perhaps for an eyelid whereas a 3-4mm punch or more is typically preferred for skin cancer biopsy purposes. A complete small skin lesion (including a rim of normal skin called the margin) may be removed with an 8mm punch.
No suture is necessary for the smallest punch biopsies. An 8mm punch biopsy will require 2 to 3 sutures. The most common size used is a 4-5mm punch biopsy which will usually require a single suture.
When is Punch Biopsy Used?
Typical reasons to perform a punch biopsy might be:
- To take a sample of a lesion where there is clinical uncertainty as to the diagnosis of skin cancer (where dermatoscopy is uncertain)
- To take a sample of a lesion that is thought to be a skin cancer – in order to determine the histological type that may influence subsequent treatment such as topical therapy, cryotherapy, and for planning margins required for surgery (wider margins are require for infiltrating BCC for example)
- To take a sample of a spreading pigmented skin cancer (lentigo maligna) on the face or neck – although an elliptical excision through the lesion (with sutures) is a frequently used alternative (there are pros and cons to each method of biopsy)
- To take a sample of a rash where diagnosis is uncertain
What are the risks of a punch biopsy?
Punch biopsy is generally considered a low-risk procedure.
There is a risk of bleeding, and damage to underlying structures is a recognised but uncommon complication (e.g. nerve damage). These risks are small to extremely small.