Fine—needle aspiration (FNA) of the thyroid has become an indispensable diagnostic modality for evaluation of thyroid lesions. Fine—needle aspiration of clinically palpable lesions is most frequently performed by the clinician (internist/surgeon/endocrinologist) with a diagnostic accuracy of approximately 80%. Ultrasound (US) guided fine—needle aspiration of the thyroid is most often performed for documented lesions that are not clearly palpable on physical exam or those which are in deeper tissues or difficult locations. Diagnostic accuracy of ultrasound guided FNA is estimated to be 90% or greater. US guidance has a distinct advantage over blind biopsy technique due to continuous real—time visualization of the nodule, needle and surrounding tissue during the biopsy procedure. Expertise in performing this manipulation comes with proper preparation and technique and will dispel initial fears about possible injury to the nearby vascularity and/or airway.

Ideally, a cytopathologist should be present during the aspiration procedure to determine the adequacy of the specimen obtained. Unfortunately, in clinical practice this is impractical, and therefore every effort should be made to provide the cytopathologist with the best slides possible. The single most important factor in adequate slide preparation is the rapid preparation of the slide and immediate application of fixative prior to degradation caused by air—dry artifact. Once adequately prepared, the slides can be evaluated off—site within 1—2 days with maintenance of diagnostic accuracy.

One suggested technique: A high—frequency (7.5 — 15 MHz) linear array transducer should be used. Multiple (near—field) focal zones are activated. The patient is prepared in much the same way as one would for a thyroid ultrasound exam with a sponge or folded pillow beneath the upper back to allow for hyperextension of the head which, in turn, maximizes exposure of the neck. The lesion to be biopsied is re—examined and the overlying skin is marked. The skin is cleansed with either betadine or isopropyl alcohol. Infiltration of the superficial tissues with lidocaine is optional, but I have found this to be helpful. A 3cc or 5cc syringe with a 25 gauge (1 1/2 inch) needle is used. Initial placement of the needle in a location just inferior or superior to the lesion is necessary to allow for visualization of the angled course of the needle into the lesion during biopsy. I prefer to confirm the initial needle location (near the skin surface) in relation to the nodule with the transducer in a transverse orientation and I use a slight rocking motion of the transducer to visualize the needle tip. This technique allows for repositioning of the needle to lie in the same sagittal plane as the lesion, if necessary. Alternatively, if the skin entry location of the needle is not altered, this allows for identification of the proper angulation, in the transverse plane, for the needle course to the lesion.

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Once the plane of the needle course is determined, I turn the transducer and perform the remainder of the examination imaging in a plane along the long axis of the needle. Sagittal imaging allows for direct visualization of the entire needle stroke length within the lesion. A few to—and—fro strokes of the needle are adequate for tissue sampling.

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I use a small amount of suction on the syringe but some elect to use no suction during needle passage. Once the specimen is obtained, the scant fluid is spread thinly over a glass slide. I have found that spreading of the fluid with use of a second slide drawn over the surface of the specimen slide at approximately a 45° angle is superior to spreading the fluid with use of the needle for preparation of a thin layer. Cytology fixative is sprayed on the specimen immediately. Some cytopathologists request that the syringe be flushed with ethyl alcohol and sent in a tube along with the prepared slide. The puncture site is then cleansed with isopropyl alcohol and the patient is slowly brought to an upright position.

Training on either a biopsy phantom or thawed turkey breast will prove to be quite beneficial as the coordination of both hands during real—time ultrasound guided biopsy requires a bit of practice before one is confident in performing this procedure. US guided fine—needle aspiration is a procedure which is quite easy to master and will allow the radiologist to remain an important interventionalist in the work—up and diagnosis of thyroid lesions.