Cytologic examination in small animals has rapidly gained recognition and clinical use. Fine-needle aspiration (FNA) is used to obtain a sample from a mass or organ that will be cytologically evaluated. This powerful tool can be used successfully for a wide variety of anatomic locations and disease processes. In many cases, it can provide a definitive diagnosis, including diagnosis of infections and some tumors.
Even if a definitive diagnosis is not possible, sample evaluation often will rule out many differential diagnoses and point toward the next best diagnostic test. The first step, and an important one, in cytologic analysis is obtaining and preparing a good sample.
Techniques for Sample
Acquisition FNA is the term applied in general to sampling a structure via a needle and subsequently dispelling the needle’s contents onto a slide for cytologic assessment. The term aspiration is often a misnomer because the easiest FNA technique, one that will provide a good sample most of the time, does not actually involve aspiration.
Note that if a mass on an internal organ or an internal lesion can be felt, it can be aspirated. However, for lesions that cannot be palpated, or for lesions near critical structures, such as major blood vessels, ultrasonography or computed tomography (CT) can be useful for guiding FNA (Figure 1).
Unless a culture will be obtained from the aspirate, preparation of the skin before FNA is almost never needed.