“What kind of tumor is it, Doctor?”
This common question is difficult, often even impossible, to answer prior to testing.
A “pre-test” administered by our pathology professor, Dr. Groth proved that merely looking at mass on a patient will rarely give us an accurate answer.
Neither will a look at the mass after surgical removal.
It seems like such a logical question. After all, the surgeon removed the growth. Didn’t he look at it prior to sending it to the pathologist?
Actually, no, he didn’t.
If a mass is removed because we fear it may be cancerous, it is crucial that the mass remain intact. Excisions are typically wide of a mass to increase the likelihood that all abnormal tissue is removed. After all, there may be microscopic cancerous cells close to a mass we can feel, invisible to the naked eye. By removing tissue as wide from the mass as is practical, we may eliminate the need to return to surgery to excise cancer left behind.
This process creates wide clean margins. The opposite of a clean margin is a dirty margin or positive margin.
Clean margins need to exist in two planes.
First, in the plane the mass exists in. If the growth is in or near the skin, a zone all around the mass needs to be removed. View the elliptical excision technique by clicking here.
Second, and just as important, in the plane perpendicular to the first. This area is referred to as being deep to the mass. Again using the skin tumor example, we would seek to remove tissues in the subcutis (just under the skin), subcutaneous fat, and even muscle tissue, if necessary.
Just as we couldn’t see a mass hidden by skin prior to surgery, after the surgery the mass is still just as hidden from every direction.
Little could be gained by the surgeon cutting into or otherwise disturbing the specimen. The diagnosis is in the cells and the cells are microscopic.
Such disturbance, however, could do much harm. When a mass arrives at the pathologist’s office his first action is to slice thin sections with a microtome. Those sections are then attached to a microscope slide, subjected to a variety of stains, and examined under a microscope.
Usually, almost any area of the mass will give the pathologist a diagnosis. However, it is the junction of the abnormal cells and normal cells that tell him whether we “got it all.” It is at that junction that margins are evaluated.
Failure to “get it all” in the case of a cancerous growth means that the patient is still at risk and, usually, means additional surgery to go back and attempt to create clean margins.
Failure to “get it all” in the case of a benign growth may mean that local recurrence is still possible, even though the cell type might not be inclined to spread to other parts of the body as a cancerous cell type might. Additional surgery may or may not be indicated, depending on the histopathologic diagnosis.
If the surgeon incises or otherwise disturbs the mass before sending it to the lab, a diagnosis may be accurate, but margin assessment may not be. Therefore, masses are submitted to pathologists intact and undisturbed.
MD oncologic surgeons have access to an intermediate step that is not available to most veterinarians, at least not those outside teaching hospitals. That procedure is called frozen section or cryosection. In this procedure a surgeon submits a surgically-excised specimen to a pathologist, it is flash-frozen to -25 degrees Fahrenheit, sliced, stained and examined. In less than 20 minutes a surgeon can have a cancer/benign, clean margins/residual cancer diagnosis. He never has to leave the patient’s side and can quickly proceed to remove more tissue, if needed. The procedure is limited, however, in that fine details of a tumor cell’s characteristics must await conventional histopathology. Even in human hospitals the wait time approaches one day.
Depending on the proximity of the lab to the veterinarian’s practice, a diagnosis may typically come five to fourteen days after surgery.
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Thanks for the thorough explanation. I knew there was a good reason why Tucker’s incision was so much larger than I expected. It does seem much better to take out a large area in case the growth is malignant than to have your pet undergo a second surgery. And our pets, unlike us vain humans, don’t really care if they have a big scar, especially one that will be covered with hair… someday.
“Scars” can be noticeable or inconsipicuous. With excellent apposition of the skin edges, avoiding trauma to the healing incision site (including infection), and good post-operative care, scarring should be minimal. Veterinarians are fortunate, in that dogs and cats have less innate tendency to scar than people. Also, scar tissue doesn’t have hair follicles. So, if scarring is excessive there may not be sufficient hair to cover the surgery site.