oncologyoutlookStick It to CancerStick It to CancerStick It to CancerAt least once daily, I’m asked by a pet owner, “My dog has had this lump on its side for some time now. What do you think it might be?”At least once daily, I’m asked by a pet owner, “My dog has had this lump on its side for some time now. What do you think it might be?”By Kevin A. Hahn, DVM, Ph.D.
At least once daily, I’m asked by a pet owner, “My dog has had this lump on its side for some time now. What do you think it might be?”
Rather than venture a guess and pick randomly from the 50-plus possible types of tumors that arise from the skin or adnexal structures, I pull out my syringe, needle, glass slides and Diff-Quik stains.
Within 10 minutes I can answer the owner’s question and, if necessary, recommend and perform appropriate diagnostic or therapeutic measures.
The cytological examination of cells from effusion or masses is a useful (and profitable) diagnostic procedure. Samples for cytological evaluation can be easily collected from many epithelial structures, body cavities and internal organs.
While cytological interpretation of fine-needle aspirates may not always yield a definitive diagnosis, it may discriminate between a benign and malignant process, justifying the need for immediate or elective surgical removal.
In one study comparing cytological versus histopathological interpretations in 147 canine skin tumors, 74 percent could be correctly identified by cytological examination.
The technique of fine-needle aspiration biopsy is rarely associated with morbidity. As with other biopsy procedures, a contraindication for fine-needle aspiration biopsy is severe coagulopathy.
Yet of all the biopsy techniques available, fine-needle aspiration poses the least risk to patients with bleeding potential if a small-diameter needle is selected and the tissues are disturbed as little as possible.
The procedure is quite simple. For superficially located palpable lesions I use a 3 cc syringe with a 22-gauge needle. I fill the syringe with about 0.5 cc of air prior to the aspiration. The most direct path to the lesion is chosen.
Before aspirating, alcohol swab the skin and part the hair to facilitate safe collection. Localize and stabilize the lesion with one hand while the other hand guides the needle, with syringe attached, through the skin into the lesion. Create negative pressure within the syringe by drawing back the syringe plunger.
Using a jabbing motion, pass the needle through several regions of the lesion. The movement of the needle should be rapid to prevent diluting the sample with peripheral blood.
The tip of the needle should not leave the lesion during the negative pressure phase. If it does, cells may be aspirated from surrounding tissues or the needle may pass completely through the lesion and pull air through the needle into the syringe.
Release negative pressure before removing the needle from the lesion. The sample may appear in the barrel of the syringe but is usually present in the lumen of the needle. Use the air in the syringe to force the needle contents onto several glass slides.
Immediately after placing the aspiration contents onto a glass slide, the material should be smeared to create a monolayer of cells for visualization after staining. Fluids or tissue samples of low viscosity should be smeared using a technique similar to that for a blood smear.
Place a single drop of the sample about 1 cm from one end of the slide. Place the edge of a second glass slide onto the middle of the slide and then back into the sample. Push the second slide across the length of the first slide to drag cell material behind it until a feathered edge is created.
For viscous fluids, perform a squash technique, in which a drop of the sample is placed on a glass slide. A second glass slide is placed on top of the sample. The sample spreads between the two slides. Downward pressure on the top slide is usually not necessary.
More viscous fluids require gentle pressure, but excessive pressure is avoided to prevent alteration of microscopic structure of the sample by causing disruption or destruction of the cells.
The cohesive effect of the fluids causes the slides to cling together. The slides are drawn apart by sliding the top slide away from the bottom slide, leaving a smear of cells and fluid in a monolayer. After air drying, slides prepared in such a manner are ready for staining.
A diagnosis of cancer is considered when the morphological criteria suggesting uncoordinated and uncontrolled growth are observed. These cytological criteria include a predominance of large monomorphic cells of various sizes.
Nuclear features characteristic of malignancy include a high but variable nuclear/cytoplasmic ratio and variability in nuclear size, shape and number. Nuclei of malignant cells often contain prominent and multiple nucleoli, abnormal mitotic figures and irregular or coarse chromatin patterns.
Cytoplasmic characteristics are not of great value in determining malignancy but can be useful for assessing the degree of differentiation and for identifying cytoplasmic granular and secretory products that suggest a specific cell type or tissue of origin.
To diagnose malignancy, a minimum of three or four criteria must be prominently displayed within a high proportion of cells examined. Highly anaplastic tumors may contain many abnormalities simultaneously.
Some malignant tumors, such as canine thyroid carcinoma, are difficult to diagnose by fine-needle aspiration biopsy because they are highly vascular and cytologically resemble peripheral blood.
It may also be difficult to diagnose a neoplasm cytologically when concurrent inflammation is present because hyperplastic changes in cells associated with inflammation can mimic malignancy.
In inflamed tumors, cytological malignancy must be interpreted cautiously, and histopathological confirmation of the lesion is recommended.
The Diff-Quik stain is the most commonly used (and inexpensive) staining procedure and provides excellent nuclear detail. However, remember that cytoplasmic granules within mast cells occasionally fail to stain and that staining time may need to be extended to two to three times longer than for peripheral blood smears.
In 10 minutes or less, the fine needle aspiration biopsy technique can provide needed information to justify additional diagnostic or treatment measures or justify a wait and see approach.
After collecting material from the mass by repeated jabbing of the needle into the tissue, squirt a small amount of material onto several glass slides. Using the dragging approach for low viscosity samples or the squashing technique for high viscosity samples allows for the formation of a monolayer of cells for observation after staining.
This represents the feathered edge of a tissue sample obtained by fine needle aspiration biopsy of a lymph node from a dog. While there is clumping in some areas, the monolayer is acceptable for identifying the presence of malignant criteria and a diagnosis of lymphoma.