Cytology: sampling and prep Flashcards
What is cytology?
- study of cells
- called cytopathology in human medicine
What is wrong with this dog?
- neoplasia of the skin
How would you take a sample from this dog?
- use a fine needle
- take the sample and put the cells on a glass slide and stain
- also used for lesions within body cavities
What are the major differences between cytology and histopathology?
Cytology:
- not highly invasive
- no need for local anesthesia/ sedation
- aspiration of individualised or grouped cells, loss of tissue architecture
- less sampling processing
- faster results
- cheaper
- not as accurate
Histopathology
- more invasive
- local anaesthesia/ sedation
- aspiration of tissue, preservation of tissue architecture
- prolonged sample processing
- slower
- more expensive
- gold standard
What are the steps of cytological diagnosis?
Describe the techniques of sample collection
- Fine needle aspiration (FNA)
- cutaneous or subcutaneous masses
- Impression smears
- exudative skin lesions and prep of cytology smears from biopsy specimens
- Tissue scrapings
- indicated in flat skin lesions that cannot be easily aspirated/ on biopsy specimens that are poorly exfoliating
- Swabs (ears, vaginal smears, fistulous tracts)
What are the 2 methods of FNA?
- Non-aspiration method: without applying suction with a syringe
- useful in highly exfoliating, highly vascular lesions/ where cells are fragile
- Aspiration method
- suction with a syringe attached to needle
- needed in poorly exfoliating masses in order to increase the cell yield
Describe the steps of the aspiration method
- mass stabilised by 1 hand
- while the needle attached to the syringe is introduced to centre of mass
- negative pressure applied using syringe to increase yield
- needle re-directed several times while -ve pressure maintained
- needle removed from syringe and air drawn into syringe
- the needle is replaced onto syringe and some of the tissue in barrel and hub is expelled into one end of glass microscope slide
What can be a potential source of contamination in the aspiration method?
- blood
- becomes a haemodiluted sample
Describe the steps of the non-aspiration method
- no negative pressure
- barrel of the syringe is filled with air prior to the collection attempt to allow rapid expulsion of material onto glass slide
- the needle is rapidly moved back and forth in a stabbing motion in an attempt to stay along the same tract
- needle is withdrawn and the material is expelled onto a clean glass slide
- used when dont want blood contamination
How can sampling errors occur? (3)
- Geographical miss
- apiration from necrotic centre
- aspiration from adjacent area of inflam
How do you make a cytology smear from excised tissue?
- tissue trimmed so that a fresh surface is created for making the smear
- surface of tissue is blotted several times against an absorbent material to remove excess blood and tissue fluid
- tissue is gently pressed several times against the surface of a clean glass slide
What are the 2 methods of cytology smear prep?
- squash prep method
- needle spread/ starfish method
Describe the squash prep method
- a portion of aspirate is expelled onto a glass microscope slide, and another is placed over the sample to spread it
- gently digital pressure can be applied to the top slide to increase spread
- smoothly slide the slides apart
- may result in excessive cell rupture
Describe the needle spread/ starfish method
- a portion of the aspirate is expelled onto a glass microscope slide
- the tip of needle is placed in the aspirate and moved peripherally, pulling a trail of the sample with it
- this is repeated in several directions (get multiple projections)
What does this show?
a well made smear
What could have caused this excessive cell disruption during smear?
- excessive pressure causing bare nuclei
This slide shows inadequate spreading - why has this occured?
- monolayer not formed - overlapping
What staining is usually used in cytology?
- Romanowsky-type
Why must smears be air dried well?
- helps cell fixation
- and adhesion to slide
What are the 2 types of Romanowsky stains?
- Aqueous based (e.g. Diff-Quick)
- Methanol based (e.g. Wright, Giemsa)
What do aqeous based stains fail to do?
- stain the granules of mast cells, basophils and large granular lymphocytes
Which picture shows methanol/ aqueous based?
- first one = methanol (see the granules better)
What does it mean if a tumour is not very granulated?
- not well differentiated
- more likely to be aggressive
