Cytologic evaluation of tissue aspirates, impressions or scrapings offers a rapid assessment of tissue pathology and is often a practical in-clinic diagnostic tool that has the ability to offer a diagnosis, aid in prognostication, direct therapeutic interventions and suggest further diagnostic testing. The ability of the sample to meet all of these goals relies on proper collection technique, slide preparation and staining, as well as the nature and distribution of the lesion and the skill/experience of the cytologist. Even the most experienced clinical pathologist will not be able to reach an accurate diagnosis if the cellularity of the sample is too low, if the smear is too thick or if the aspirated tissue is not representative of the observed lesion. In addition, some lesions cannot be diagnosed cytologically despite proper collection, smear preparation and staining, as tissue architecture may be required or cells may not exfoliate readily from some lesions. In these cases histopathology is necessary.
