Ultrasound-guided FNA of the thyroid
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Ultrasound-guided fine needle aspiration (FNA) of the thyroid refers to a minimally invasive procedure where in which tissue samples are collected from a thyroid nodule or other suspicious thyroid lesion. It is usually done on an outpatient basis and generally complications are very minimal.
The procedure is similar to fine needle aspirations elsewhere in the body, although the superficial location of the thyroid may make targeting easier. Technique for thyroid FNA varies widely from institution to institution, but there are elements common to all procedures.
linear high-resolution ultrasound probe (>9 MHz)
22-27 gauge needle (fine needle) 4/ spinal needle 5,6
antiseptic agent (povidone iodine, chlorhexidine, etc)
10 mL of 1% lidocaine (optional)
5-10 mL syringe for the needle (optional)
ultrasound needle guide (optional)
a pathologist or cytotechnologist (optional)
the nodule is localized with the ultrasound transducer
if using a guide, the guide path should not traverse important adjacent structures (e.g. carotid artery)
keeping the needle parallel to the transducer allows more of it to be seen and is often more useful in localizing the tip
the skin is cleaned with the antiseptic agent
a sterile probe cover is applied
many practitioners inject 1-2 mL of 1% lidocaine into the superficial tissue over the area of interest
the patient should be instructed not to swallow or speak when the needle is below the skin surface
the 22-27 gauge needle is guided into the lesion
a to-and-fro action is used when the needle tip enters the nodule
cells from the nodule enter the needle with capillary action
some practitioners use suction with a 10 mL syringe, but this is controversial since others think it only adds blood to the sample
the aspirated material is placed on a slide and often is checked by a pathologist/cytotechnologist for diagnostic quality
multiple passes (usually 3-5) are performed per nodule
Complications are minimal if the tip of the needle is visualized throughout the procedure. Possible complications are mild localized pain radiating to the ear or localized hematoma. The superficial location of the thyroid allows easy compression of bleeding.
While ultrasound guided FNA remains the recommended procedure for investigation of thyroid nodules, non-diagnostic samples remain a clinical dilemma. Non-diagnostic rates in the literature have been described ranging from 4-16% 3. FNA results are usually reported according to the Bethesda classification system.
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