Many dermatology patients will undergo a skin biopsy at some point during their lives, especially if they have a new lesion that could potentially be a skin cancer. During a biopsy, a sample of body tissue is taken so that a type of doctor, known as a pathologist, can examine the individual cells in the tissue under a microscope in order to make a more definitive diagnosis. If a dermatologist finds a new skin lesion during a physical exam, it may be difficult to see with the naked eye if the lesion is a cancer, and a biopsy is helpful to determine the exact morphology.
These biopsy results can also help guide the ideal treatment plan. For example, to diagnose and treat skin cancer, a biopsy is necessary to verify the type and grade of cancer and, at time, to determine how deep it is.
Biopsies can be performed on almost any area of the body by many different doctors, but for now we'll focus on skin biopsies. Skin biopsies are generally quick procedures that are done in an outpatient office. They are relatively safe, and your dermatologist will go over risks and benefits before the procedure. There are several types of skin biopsies, but the main two we will discuss here are shave and punch biopsies. Both procedures begin with cleansing of the area to be sampled, as well as injection of a local anesthetic, but they differ in the method by which the tissue sample is removed.
Shave biopsies are one of most commonly performed procedure in dermatology clinics. They are typically used in diagnosing lesions involving the outermost layer of the skin, the epidermis. These can be useful in diagnosing certain skin cancers, such as basal or squamous cell carcinomas. Once the area has been prepped, a straight razor is used to peel off a section of tissue parallel to the skin. You can imagine this procedure in a similar way to peeling a carrot: this type of biopsy allows dermatologists to sample a little bit of the epidermis and dermis without having to go very deep (although depending on the clinical scenario, a deep shave may be warranted).
A punch biopsy is a little different than a shave biopsy and has a few additional steps. In this method, a circular instrument penetrates all the layers of the skin, a cylindrical tissue sample is taken out, and a suture or sutures may be used to close up the skin where the sample was taken. The punch instrument can be thought of as a much smaller version of an apple corer that goes just far enough to penetrate the skin and a little bit of the subcutaneous fat beneath it. There are many different sizes of punches that can be used depending on what the dermatologist needs, but most are smaller than a pencil eraser (6mm). Once the sample is taken, a suture can be placed to draw the edges of the skin together and the patient is able to go home. These biopsies are better suited for helping diagnose deeper tissue lesions and some rashes.
One final type of biopsy to briefly mention is an excisional biopsy. In this procedure, a scalpel is used to cut out the entire skin lesion along with an area of normal skin, multiple sutures are placed, and the entire sample is sent off to be analyzed. This type of procedure takes longer, is more involved, and is less frequently used for initial evaluation of a lesion than a shave or punch biopsy is.
While shave and punch biopsies are obtained in different ways, the tissue samples from both are very useful for establishing a definitive diagnosis. Your dermatologist will know which type of biopsy is best for you and the results from the biopsy will help your dermatologist reach a more conclusive diagnosis and provide the most appropriate treatment.