Why are FNAs performed
A FNA is a type of biopsy. In a biopsy a small sample of tissue is removed for examination by a pathologist. The doctors look at the samples under a microscope and may stain the cells with different dyes to help them distinguish between normal and abnormal cells. The possible results are listed below.
Procedure
FNA is done with a small, 20-27 gauge, needle (same size or smaller than most needles used in ordinary blood test, a larger gauge corresponds to a smaller needle). The area is sterilized with alcohol to prevent infection. The needle is then inserted and aimed at the center of the lesion. When the needle reaches the lesion a very small piece is removed by suction. This is repeated to ensure that a proper amount of usable sample is obtained. Local anesthesia is not used in most cases because the sting from a local anesthesia needle is more painful than the FNA procedure itself. If the lesion is non-palpable the doctor may use ultrasound or other imaging techniques to help guide the needle precisely into the suspicious lesion.(1)
Analysis
Samples are sent to a pathologist specially trained in cytology (cellular abnormalities) to be processed and interpreted. The samples are placed on glass slides and stains are used to reveal the details of the cells. The diagnosis will generally come back as one of five options:(1) (2)
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Benign - the mass is not of much concern and will not cause any significant problems as long as it remains unchanged.
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Atypically indeterminate - a diagnosis cannot be obtained from the sample. Other tests are needed to determine the nature of the lesion.
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Suspicious/probably malignant - not a diagnosis of cancer. This type of diagnosis requires additional investigation because the sample has abnormal characteristics. This lesion should be biopsied with a more complete method to determine whether a malignancy (cancer) is present.
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Malignant - a diagnosis of cancer; should be biopsied and tested for exact tumor makeup to prepare for treatment.
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Unsatisfactory - a diagnosis cannot be determined from the sample because of insufficient sample size, processing or other machine or human errors.
The Triple Test (TT) Method
After the biopsy is diagnosed by a pathologist all aspects of the case should be considered by a clinician, this is called the triple test method or TT. The triple test method considers the results of the physical examination, imaging (mammography, MRI, etc.) results and the cellular (cytological) findings of the pathologies (based on the biopsy samples). When all of these aspects are considered a FNA is very accurate. The false positive and false negative rates are similar to biopsies obtained by more invasive surgeries. The TT method should always be used to diagnosis a breast mass using FNA.(1)
Preparation and Side Effects
There is no special preparation for a FNA, no fasting, special diet, etc. In almost all cases FNA will be done in the doctor's office and not in a hospital. There is very little pain associated with a FNA and the procedure is very safe, resulting in only a little bruising and tenderness around the biopsy area.
View a table comparing Fine Needle Aspiration with Core Needle Biopsy
Go to the biopsy page to watch a documentary about biopsies, including FNA.
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