Terminology
CPD ACCREDITED ARTICLE CPD ACCREDITED ARTICLE
Terminology
• Hypertrophy : An increase in cellular size and / or functional activity in response to a stimulus .
• Hyperplasia : An increase in cellular numbers in response to a stimulus . Increased mitotic activity is a common finding . This is a reversible change . Example – generalised reactive hyperplasia of lymph nodes seen with chronic canine ehrlichiosis .
• Neoplasia : An increase in cellular growth and multiplication that is not dependent on a stimulus external to the neoplastic tissue .
• Metaplasia : A process where one mature cell type is replaced by another mature cell type . This change is seen as an adaptive replacement that is reversible e . g . chronic rhinitis .
• Dysplasia : A reversible , irregular , atypical , proliferative cellular change in response to irritation or inflammation . Can be confused with malignant changes .
• Anaplasia : A lack of differentiation of tissue cells . Usually an indicator of malignant potential .
• Dyscrasia : An increase / decrease in the numbers of one or more cell components / maturational stages of a tissue out of proportion to other cell components / maturational stages .
1 . Fine-needle aspiration ( FNA ) The sample is collected with a 22-25 G needle and a 3-20 ml syringe . The softer the tissue is , the smaller the needle and syringe that should be used . With larger needles , tissue cores with few free cells are aspirated and blood contamination ( haemodilution ) is more common . Softer tissues such as lymph nodes are aspirated with a 3 ml syringe , whilst firm tissues such as fibromas and squamous cell carcinomas require a larger syringe to maintain adequate negative pressure / suction in order to collect sufficient cells . If the texture of the tissue is unknown , a 12 ml syringe should be used .
Skin preparation is similar to that required for venipuncture , i . e . an alcohol swab can be used to clean the area . In the case of ultrasound-guided aspiration , it is very important to clean the skin of any ultrasound gel before sampling , as even a very small amount of ultrasound gel contamination during aspiration could obscure cells and render a slide non-diagnostic .
There are 2 basic harvesting techniques .
• Aspiration technique The mass is stabilized between thumb and forefinger , while the needle with syringe attached is introduced into the mass . The plunger is withdrawn two-thirds to three-fourths the syringe volume . If the animal is calm enough and the mass is large enough , the needle is redirected in the mass while negative pressure is maintained . With small masses and fractious animals , negative pressure is released , the needle redirected and negative pressure then reapplied . Negative pressure is released before the mass is exited to
prevent the aspiration of surrounding tissues , the aspiration of the sample into the needle hub / syringe and excessive blood contamination . After several areas of the mass have been sampled , negative pressure is released , the needle removed from the mass and then the needle is removed from the syringe . Air is drawn into the syringe , the needle is replaced and the sample is forced onto a clean glass slide . The material is smeared and allowed to air dry .
• Stab technique This technique relies only on the passage of the needle through the tissue to collect enough cells , and not negative pressure . Most commonly , a needle without an attached syringe is used , but a syringe can be connected to use as a handle only . No negative pressure is applied during collection . The hub of the needle is grasped with thumb and forefinger ( as if throwing a dart ), the mass is stabilized and the needle is inserted into the mass . About 8 – 10 stabbing motions are made , staying in the same tract , but making sure that the tip of the needle stays inside the mass so that contamination by surrounding tissues is avoided .
The needle is removed from the mass ; a syringe with plunger drawn back attached , and the material expelled onto a clean glass slide . It is then smeared and left to air dry . This procedure must be repeated in multiple areas of the mass . If multiple masses are sampled , always use new needles and syringes with each mass .
2 . Impression smears Impression smears ( also called imprints ) can be made of superficial cutaneous lesions or from tissues obtained by surgical biopsy . Ulcerative lesions must be imprinted , then cleaned with a moistened surgical swab and again imprinted . Freshly cut surfaces from biopsy samples must be blotted with absorbent paper repeatedly until dry of blood , and gently touched to the surface of a clean microscope slide , without a smearing action , as this will rupture cells .( Fig 2 )
Fig 2 : Impression smear being made from a blotted freshly cut edge of a biopsy sample vet360
Issue 01 | MARCH 2018 | 26