The types of skin biopsy in dogs are various and the choice of one over another is often a matter of evaluating which one is most suitable for the type of lesion involved. There are several pros and cons for each type and some types of skin biopsy in dogs don't even require general anesthesia which is a big plus to dog owners concerned about putting their dogs under. Once the biopsy is collected, the sample will then be sent out to a pathologist for evaluation. The pathologist will then send his/her findings back with a possible diagnosis.
Obtaining a Skin Biopsy in Dogs
A skin biopsy is often the most important piece of the puzzle when it comes to diagnosing and evaluating potentially malignant skin conditions affecting dogs. The skin biopsy results must be interpretated very carefully along with other pieces of the puzzle such as bloodwork, x-rays and other diagnostic modalities.
Care must be taken in obtaining a biopsy sample following standard preparations (sample placed in 10 percent buffered neutral formalin) and then submitting the labeled sample to a highly trained pathologist. The pathologist will then evaluate the patient's clinical information provided and look at the sample under a microscope.
On top of preparation protocols, there are several general guidelines vets tend to adhere to. Obtaining a large sample as possible is important so to promote an accurate diagnosis by the pathologist. The incision should be typically made in a certain direction, "like the stripes on a tiger" to minimize skin tension so that, should a future surgery be needed, the surgical procedure will be easier.
Obtaining a skin biopsy in dogs is generally low risk. Complications are mostly seen in dogs with underlying bleeding disorders which may be prone to uncontrollable hemorrhaging (bleeding). This can be avoided by having dogs undergo testing to rule out bleeding abnormalities. Infections at the biopsy site are always a possibility, but can be easily avoided following strict aseptic techniques. And of course, in cases where anesthesia is needed, negative reactions to the anesthesia may be a possibility in certain dogs.
Types of Skin Biopsy in Dogs
There are several different types of skin biopsy in dogs: punch biopsy, incisional or wedge biopsy, excisional biopsy and needle core biopsy. Let's take a closer look at each.
A punch biopsy is taken by using an instrument known as a Baker's biopsy punch. Thi procedure is indicated for any skin lesions. After the hair is clipped and the surgical site has been prepped, lidocaine (a local anestethic to numb tissue) is injected around the area that needs biopsied.
The area is then disinfected once more, the skin is then stretched between the thumb and index finger and the instrument is placed to obtain a sample ranging in size from 2mm to 8mm. Generally, larger samples (6- or 8-mm) are preferred, since, as mentioned, this helps aid the pathologist in obtaining a potential diagnosis. Small samples are generally used for growths near the eye, on the ear, and on the bridge of the nose or footpads. Finally, once the sample is obtained, one to two sutures are placed to close the skin.
The main advantage of a punch biopsy in dogs is that general anesthesia is generally not required for this procedure. A disadvantage though is that the small sample might not always be diagnostic.
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Wedge Biopsy (Incisional Biopsy)
In some cases, a larger sample compared to the one obtained by punch biopsy may be desirable for diagnostic purposes. This larger "wedge" sample offers the advantage of allowing the pathologist to more easily detect any characteristics which may be potentially be suggestive of a malignancy.
This is a more invasive biopsy technique as it involves an incision, and therefore, often requires general anesthesia. All dogs benefit from screening tests to identify blood clotting disorders or metabolic diseases.
In this procedure, the dog is placed under general anesthesia, the hair is clipped and the surgical site is prepped. Next, an elliptical (oval, egg-shaped) or wedge incision is made, blood vessels are ligated, the sample is taken using a scalpel blade and then sutures are placed to close the incision.
This type of biopsy is in many cases diagnostic, but not only, therapeutic to a certain extent as well considering that it removes the entire growth. It is often indicated when a lesion is located in an area that permits wide surgical removal without negatively affecting the healthy tissue surrounding it.
Generally, prior to an excisional biopsy, the vet would have performed a fine needle aspirate and provided the surgeon with the results so the surgeon is equipped with as much information about the growth as possible. This is important, considering that certain types of cancer such as mast cell tumors or soft tissue sarcomas requires wide surgical margins (2 to 3 centimeters) , whereas; a sebaceous cyst or sebaceous adenoma requires much smaller margins.
The main advantage of this type of biopsy is the fact that the large tissue sample often provides quite an accurate diagnosis. However, it require general anesthesia. The procedure is the same as in the case of the incisional biopsy with the only difference that the lesion is removed entirely and with adequate margins.
Needle Core Biopsy (Tru-cut)
A needle core biopsy is quite a fast and safe skin biopsy procedure. It is indicated for skin or under the skin lesions. A needle core biopsy offers the advantage of being performed on an awake dog when cooperative. It is slightly though more invasive than a fine needle aspiration due to the spring-loaded Tru-cut biopsy needle's diameter being more than a regular vaccine needle.
A needle core biopsy may be performed using a core biopsy needle or a Tru-Cut biopsy needle. Generally, in this procedure, the biopsy site is prepped and lidocaine is injected around the lesion. A surgical blade is used to make a stab incision through the skin so to allow easy access of the needle to obtain the biopsy. The stylet (a slender probe) is advanced into the tissue requiring biopsy. Next, the outer cannula is advanced over the stylet allowing the vet to cut off the tissue that is left in the notch of the stylet. The tissue sample is then removed from the stylet.
Although the small tissue sample may not be always diagnostic, compared to fine needle aspiration, generally, the results are more accurate. However, the results may never be as accurate as in the case of an excisional biopsy.
Managing the Veterinary Cancer Patient, Gregory K. Ogilvie, Anthony S. Moore, Veterinary Learning Systems