Ultrasound-guided FNA of the thyroid

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 a outpatient basis and generally complications are very minimal.

Procedure

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.

Equipment

• linear high-resolution ultrasound probe (>9 MHz)
• 25-27 gauge needle (fine needle)
• antiseptic agent (povidone iodine, chlorhexadine, etc)
• 10 mL of 1% lidocaine (optional)
• 5-10 mL syringe for the needle (optional)
• ultrasound needle guide (optional)
• a pathologist or cytotechnologist (optional)

Technique

• the nodule is localized with the ultrasound transducer
  • if using a guide, the guide path should not traverse important adjacent structures (e.g. the carotid)
  • keeping the needle parallel to the transducer allows more of it to be seen and is often more useful in localising 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 25-27 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 other think it adds only blood to the sample
• the aspirated material is placed on a slide and often is checked by a pathologist or cytotechnologist for diagnostic quality
• multiple passes (usually 3-5) are performed per nodule
• depending on the situation, aspirated material may be reserved for cell block cytology or gene expression classifier tests

Complications

Complications are minimal if the tip of the needle is visualised throughout the procedure. Possible complications are mild localized pain radiating to the ear or localized haematoma. The superficial location of the thyroid allows easy compression of bleeding.

Outcomes

US guided FNA remains the recommended procedure for investigation of thyroid nodules, but nondiagnostic samples remain a clinical dilemma. Nondiagnostic rates in the literature have been described ranging from 4-16%³.