During a routine visit, an owner points out a mass on the medial hock of her 6-year-old boxer.
A strange-looking 8–year-old German shepherd has a huge nasal mass.
A 10-year-old Labrador has a large, firm mass along the entire caudal thigh.
What are your rule-outs?
What do you tell your clients?
• “Just watch it.”
• “Come back for a recheck in six months.”
• “Big surgeons make big incisions. Let’s amputate the body part in question.”
• “I would recommend further testing.”
Obviously, all Veterinary Practice News readers chose the fourth and only reasonable answer. The classic expression “Just watch it” has been dubbed the three deadliest words in veterinary medicine.
Yes, “further testing” is in order. Either a fine-needle aspirate (FNA) or a biopsy should be performed. Because they provide information about the architecture, in addition to the cell types, biopsies tend to be more accurate and informative than FNAs.
Here are some suggestions for taking biopsies.
Core Biopsy
For skin and subcutaneous masses, many surgeons favor a spring-loaded Tru-cut biopsy needle. There are a variety of manufacturers, diameters and lengths. What is needed depends on the nature and the size of the mass.
There are typically two firing modes so that a short or a long sample can be harvested. It is slightly more invasive than an FNA, only because the diameter of the needle is larger than an injection needle. This should be a sterile procedure, performed under heavy sedation or anesthesia.
The biopsy site is clipped and scrubbed, and sterile gloves are worn.
The tip of the needle is placed into the mass through the skin, which creates only a small opening. This allows obtaining samples in multiple directions through the same hole. When the device is activated, it cuts a small core of tissue (hence the name “needle core biopsy”) and protects it within the cylinder.
The needle is retrieved and primed by pulling on the handle. Then the core of tissue is gently placed on a piece of sterile paper, such as a corner of the paper wrap of your sterile gloves. If necessary, a 25 G needle can be used to carefully help transfer the sample.
The primed needle is ready to be used for the next sample.
Once enough representative samples are collected, the corner of the paper is cut off and placed in formalin (see box and “Web Exclusive”). It is very important to respect the magic ratio to attain sufficient fixation of the sample: one part tissue to 10 parts formalin.
The small nick in the skin is usually left to heal by second intention. If the patient bleeds, a simple interrupted suture can be placed in the skin along with a light bandage. Although they are theoretically designed for single use, most veterinary surgeons probably re-sterilize Tru-cut biopsy needles with ethylene oxide as long as they are sharp and not bent.
A key factor to increase the chances of actually obtaining a diagnosis is that soft tissue biopsies should be taken from the periphery of the mass. The center of the mass may be necrotic and yield useless or little information. It can even give a false negative result.
Incisional Biopsy
Incisional biopsies are slightly more invasive. In most cases, a short, linear skin incision is sufficient, and one or several wedge biopsies are taken with a scalpel blade. Alternatively, some practitioners prefer to use a biopsy punch, which is perfectly adequate. A couple of sutures close the skin.
Whether a needle core biopsy or an incisional biopsy is harvested, it is critical to plan ahead and make a skin puncture or incision that will be easy to remove at the time of a possible excision later on. This precaution will avoid the potential seeding of cancer cells along the biopsy tract.
Excisional Biopsy
A more efficient way of dealing with a skin mass is to seek diagnosis and treatment in the same procedure. This is the excisional biopsy. The choice between an incisional and an excisional biopsy depends on several medical and financial factors. For instance, if money is an issue, a client may have to decline one step.
However, if a skin mass could just as well be benign or malignant, taking a needle or incisional biopsy may be in the patient’s best interest. Otherwise, wide margins may be taken unnecessarily on a benign mass or, worse, narrow margins may be obtained on a malignant lesion.
In other words, there is no justification for taking 3 cm margins when dealing with a (benign) histiocytoma.
Whichever type of biopsy is chosen, it is important to help the pathologist help you by providing the location of the mass, the type of biopsy performed and a brief clinical history.
The Answers
So what was your diagnosis?
The correct answers are: The boxer had a mast cell tumor, the German shepherd had a fibrosarcoma and the Labrador has a perfectly benign intermuscular lipoma.
Success in treating a patient is directly correlated to our ability to reach the correct diagnosis. Providing good-quality tissue samples to a trusted pathologist is therefore crucial. Next time you see a patient with a skin mass, remember the oft-repeated advice: “Biopsy, biopsy, biopsy.”
Dr. Zeltzman is a small animal board-certified surgeon at Valley Central Veterinary Referral Center in Whitehall, Pa. His website is www.DrPhilZeltzman.com.
Formalin is Highly Toxic
Formalin is often handled nonchalantly but it is a highly toxic fluid.
Formalin is a solution of 37 percent formaldehyde gas dissolved in water. Formaldehyde is a toxic gas that irritates the eyes and respiratory tract. It is also a known carcinogen.
Therefore, these little jars of formalin, a potent tissue fixative, should not be handled casually. They should be kept closed until it is time to transfer the biopsies. Leaving the jar uncapped exposes everybody around to toxic carcinogenic fumes. Beyond the medical concerns, some obvious liability issues exist.
In case of exposure, the National Institute for Occupational Safety and Health recommends copious irrigation of eyes and skin that have been exposed.
Side effects include irritation of the eyes, nose, throat and respiratory system; asthma; conjunctivitis and lacrimation; coughing; wheezing; or dermatitis.
The biggest concern is cancer, mainly of the upper airways.
Safety measures should include wearing a mask, gloves and eye protection.
