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The technique is not a strictly aspetic procedure, but it is wise to clip the area and swab with alcohol. The mass/lymph node is immobilised with one hand and a 23 ga needle +/- a 5 ml syringe is inserted into the lesion. The sample is obtained in 1 of 3 ways:
A. “Needle only” method
This method is useful for aspirating soft masses and lymph nodes and has the advantages that delicate, fragile cells are not damaged by suction and haemodilution is minimised.
B. “Continuous suction” method
This method is useful for aspirating firm masses such as fibrosarcomas which tend not to exfoliate cells well.
C. “Intermittent suction” method
This method is suitable for small masses where it is not possible to redirect the needle without exiting the mass.
An air-filled syringe is attached to the needle (if the syringe was already attached to the needle it should be disconnected from needle, filled with air and then re-attached to the needle). Holding the tip of the needle over a clean glass slide, the plunger is briskly depressed, thus expelling the contents of the needle onto the slide (image 1 above) (now referred to as slide 1), or, if there is a high harvest, distributing between 2 or 3 slides laid side by side.The sample is then smeared using the squash preparation technique. NB it is very important to smear the sample rather than just squirting it on to a slide, since the cells must be in a monolayer to be evaluated.
A. Squash preparation.
Slide 2 is slid quickly and smoothly across slide 1, (image 4 above)
The smear is on the lower surface of slide 2
With experience this technique produces excellent smears. Practice is required!
For turbid samples the blood smear technique is used (see preparing a blood film), or can be modified with the line concentration technique.
The sample is smeared as for the blood smear technique, but when the spreader slide has been advanced about two-thirds of the way across the slide the spreader slide is abruptly lifted upwards. This produces a smear with a concentrated line of cells at its end, instead of a feathered edge
These techniques are useful in obtaining material from ulcerated cutaneous masses where cells can be collected directly from the lesions’ surface. However, cells obtained from the surface are not necessarily representative of the whole lesion. The surface of ulcerated tumours often become secondarily infected and imprints and scrapings may harvest only the superficial inflammatory cells and not the underlying neoplastic cells. Thus these techniques are not always useful in the diagnosis of neoplasia. Inflammatory lesions such as eosinophilic granuloma complex may be readily diagnosed with impression smears or scrapings.
Impression smears may also be made from the cut surface of tissues obtained at surgery or post mortem. Blood and tissue fluid should be removed by blotting the sample dry before touching the sample onto a slide.
A swab or cotton bud is used to collect samples from fistulous tracts and from the vagina. Unless the lesion is very moist the swab must first be moistened in isotonic saline. The swab is rubbed against the surface of the lesion and then gently rolled along a slide, taking care not to rub the swab across the slide since this would damage the cells.