This is the second article in a series aimed at defining some of the more common terms used in oncology. Having an excellent understanding of these terms will help you to make better decisions for a pet with cancer and will also help you to do a better job supporting friends and family members after a cancer diagnosis.
If you missed last week's article, you can check it out here.
The terms defined in this article will focus on the diagnosis of cancer.
Part 2 -
This is a simple procedure involving the brief placement of a small needle into a mass or organ to extract cells and establish a diagnosis. The cells are transferred from the needle to a glass slide using a syringe. The cells are stained using H&E, which makes them visible under a microscope. The slides are usually sent to a pathology lab for diagnosis by a clinical pathologist.
In many cases, an aspirate alone can yield a diagnosis. [Ex. If a lymph node is enlarged, a veterinarian will usually aspirate the lymph node as a means of determining if lymphoma is present or not].
This is the study of cells. When cells are obtained from a mass or organ using an aspirate, the description of the cells and the diagnosis is written in a cytology report.
A biopsy involves taking a small piece of tissue (not just cells) from a mass or organ to obtain a diagnosis. This is a small procedure that is typically performed under heavy sedation, although some biopsies require anesthesia.
Since a biopsy is more involved and more expensive than an aspirate (the results also take longer), veterinarians usually start with an aspirate if they think there is a reasonable chance it will provide a diagnosis.
A biopsy is more likely to provide a diagnosis than an aspirate because by giving the pathologist a piece of tissue (instead of just cells), we are giving them more information to work with (but it's more involved and more expensive). In addition, a biopsy can provide tumor grade, where an aspirate cannot.
Since a biopsy involves taking a small piece of tissue, the veterinarian will often place a couple of sutures at the biopsy site, will send home a few days of pain medication, and will send your dog home with an e-collar to prevent licking of the biopsy site (and subsequent infection).
This is the microscopic study of abnormal tissues.
When a mass or an abnormal organ is removed and submitted to the pathology lab, the histopathology report is the information that is returned with a description of the tissue as well as the diagnosis. This report (unlike cytology) can give us the tumor grade (how aggressive it might behave), the specific type of tumor present, and tell us whether margins have been obtained (whether all of the tumor cells have been removed or not - more on this in the next post!).
This is the image produced by x-rays. For veterinary oncology purposes, radiographs (which are digital these days) are most commonly used to evaluate the thorax (chest), and more specifically, the heart and lungs. Since many types of cancer can spread (metastasize) to the lungs, taking radiographs is an essential part of any workup for a cancer patient. In order to properly determine if there is evidence of cancer in the lungs, 3-view thoracic radiographs must be performed. This means that three different radiographs are taken of the chest - one with the patient laying on their left side, one with them laying on their right side, and one with the patient laying on their back. Radiographs should be read and interpreted by a board-certified veterinary radiologist for the highest level of accuracy.
The use of high-frequency sound waves, which bounce off tissues based on variations in density to produce an image. In veterinary oncology, ultrasound is commonly used to evaluate the abdominal organs.
Abdominal ultrasound is a very common tool used to assess all of the abdominal organs and determine if cancer (or another abnormality) is present. The ultrasonographer is looking for "normal" vs "abnormal". If an organ appears abnormal (either because it is enlarged, too small, or there is a mass present, or if it is too bright or too dark) the next step is to determine why the abnormality is present, which often involves taking an aspirate.
The ability of ultrasound to detect disease is highly dependent on (1) the skill of the clinician performing the ultrasound, (2) the quality of the ultrasound machine, (3) the patient (they need to be laying still, not panting excessively, their fur needs to be adequately shaved to allow appropriate imaging).
(7) CT scan:
CT (computed tomography) scan uses a combination of X-rays and a computer to create a 3-D image of the body part being imaged.
You can think of the information gathered by a CT as being represented by a loaf of bread. If someone wanted to take a closer look at a certain section, they would be able to select an individual "slice" of that loaf and look at it like you would a radiograph (in black and white). If you were performing CT of the abdomen, you would be able to choose any section of the abdomen and see it in significantly more detail.
We commonly perform CT of the chest, spine, abdomen, or of tumors themselves. Each slice may be 1 mm or less (very thin!), depending on the age of the machine and its capabilities.
There are cases when x-rays and ultrasound do not give us as much detail as we need. In those cases, CT is needed.
Even though MRI is typically the preferred means of evaluating soft tissue over CT (and CT is favored over MRI for evaluating bone); CT is still used more for soft tissue in veterinary medicine due to its accessibility.
CT is usually a quick procedure. Patients may be either sedated or anesthetized, depending upon the specific organ being evaluated.
Magnetic resonance imaging (MRI) uses magnets and radio waves to create images of structures inside the body. It is especially good for imaging the brain and spinal cord.
Patients are always anesthetized for MRI studies. Just as with CT, MRI is used to evaluate an entire "section" of a patient, such as a brain. You can then use computer software to examine a single "slice" or section of the scan more closely, in order to gain more information about abnormalities.
Dr. Lori Cesario
Board Certified Veterinary Oncologist
PS: I'm happy to now offer online oncology consultations. Learn more about how this service can help by visiting the Vet Cancer Consultants site.
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