Thyroid FNA Tests 

Fine-needle aspiration (FNA) of the thyroid is used to differentiate benign versus malignant pathology of thyroid nodules.

Thyroid nodules are relatively common in the general population. The key to evaluation of these nodules is to determine which represent cancer and therefore require further therapy.

The incidence of thyroid carcinoma has more than doubled over the past 30 years. Some attribute this trend to increased detection of small papillary cancers.^{[1, 2]} Up to 67% of asymptomatic individuals have thyroid nodules found on high-resolution ultrasonographic imaging, and up to 8% of the general public have palpable nodules.^[3]

To differentiate benign versus malignant pathology, the evaluation of a thyroid nodule generally consists of thyroid function tests and FNA.

Large-scale studies have shown that the sensitivity of FNA for identifying thyroid malignancy is 91.8% and the specificity is 75.5%.^[4]

Category

Fine-needle aspiration, thyroid

Device details

There are numerous hypodermic needle manufacturers. The following are examples:

• BD
• Terumo
• Exel International

By definition, FNA biopsy involves a needle that is 22 gauge (0.72 mm outer diameter) or smaller. Most physicians use either a 23- or 25-gauge 1.5-inch hypodermic (hollow) needle with a standard bevel. This is screwed onto a 10-mL syringe with a male Luer-Lok connection fitting.

Additionally, some commercially available FNA needles have added features to assist with biopsy. One example is the Inrad FNA biopsy needle, which is coated with anticoagulant and has a clear hub to view the aspirate.

In addition, some physicians use syringe holders that they find helpful when performing FNA. The Cameco syringe pistol (Precision Dynamics Corporation, Burbank, CA) and the Tao Aspirator (Tao Technology, Incorporated, Carmel, IN) are syringe-holding devices. The Cameco syringe pistol is nondisposable and is the most commonly used assistive device. The Tao Aspirator is a relatively new FDA-approved syringe holder with a pencil grip to allow for fine motor control.

According to the updated American Thyroid Association Guidelines for management of thyroid nodules and differentiated thyroid cancer, FNA has a key role in the evaluation of thyroid nodules identified with palpation or ultrasonography.^[5] The recommend evaluation of these patients begins with a history, physical examination, and thyroid stimulating hormone (TSH) study. If the TSH level is low, nuclear imaging is recommended to evaluate the patient for hyperthyroidism.

Patients with a nonfunctional thyroid nodule and those with a normal or high TSH levels should undergo diagnostic ultrasonography of the thyroid. If no nodule is found, FNA is unnecessary. If a nodule is found on ultrasonography, FNA is recommended. Results of the FNA determine if further therapy is needed (see table below).

Table 1. FNA Results and Recommendations (Open Table in a new window)

An alternative method of reporting thyroid cytopathology is the Bethesda System^[6] . In The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), it is recommended that every report begin with 1 of 6 diagnostic categories. Clinicians can use the diagnostic category and the implied risk of malignancy to guide treatment planning (see table below).

Table 2. Bethesda System (Open Table in a new window)

Contraindications

FNA has no absolute contraindications.

Large-scale studies have shown that the sensitivity of FNA for identifying thyroid malignancy is 91.8% and the specificity is 75.5%.^[4]

Results of a randomized controlled clinical trial showed that ultrasonography-guided FNA yielded a tissue adequacy rate of 84%, as opposed to 58% for the standard palpation technique.^[7]

Preparation

Anesthesia

FNA can be performed quickly and comfortably in the office or at the bedside. Anesthesia is unnecessary but recommended for patient comfort.^[8] Infiltrative anesthesia with lidocaine can be injected subcutaneously over the nodule. Alternatively, ethyl chloride can be applied topically. The container should be held upside down and positioned 3-9 inches away from the skin. It should be sprayed for 4-10 seconds or until the skin starts to turn white (see table below).

Table 3. Medication Summary (Open Table in a new window)

Equipment

A 23- to 25-gauge needle is loaded onto a 10-mL disposable syringe (see image below).

Two slides are needed for each pass, so 6 glass slides should be available. Slides can be air dried or sprayed with 95% ethyl alcohol for sample fixation.

Numerous buffered solutions are available for cell transport and slide preparation. The senior author uses CytoLyt, a methanol-based buffered solution.

Ultrasonography, if available, can also be used to guide the FNA. The advantages of ultrasonography-guided FNA include the ability to identify features associated with malignancy and to avoid important structures. In larger nodules, it also allows the physician to focus the biopsy in the area of concern.

Positioning

The patient can be positioned either sitting upright or supine. A pillow or shoulder roll can be placed behind the shoulders to extend the neck.

Complication prevention

The anterior jugular veins can sometimes be visualized and should be avoided during this procedure. In large goiters, the contents of the carotid sheath are at risk, so ultrasonography or CT guidance is recommended.

Technique

With the patient lying supine or erect with the neck flexed, the thyroid nodule is palpated. If ultrasonography is being used, the nodule is localized and characterized. The neck should be inspected for superficial vessels such as the anterior jugular veins, which should be avoided. In patients with large goiters and in postsurgical patients, the location of the carotid artery and jugular vein should be estimated. Once the nodule is localized, the skin overlying the planned FNA site is cleaned with alcohol and anesthetized. If lidocaine is used, 3-5 minutes should be allowed for adequate analgesia. Ethyl chloride works almost immediately, whereas topical anesthetics may require up to 1 hour for maximal effect.

The skin overlying the nodule is cleaned with either alcohol or Betadine. A 10-mL disposable syringe is then loaded with the FNA needle. Most commonly, an 18- or 23-gauge needle is used. After allowing for adequate anesthesia, the needle is inserted into the nodule and aspirated. Multiple passes are performed while applying negative pressure via the syringe. Next, the contents of the needle are evacuated onto a glass slide.

Results of a randomized controlled clinical trial showed that ultrasonography-guided FNA yielded a tissue adequacy rate of 84%, as opposed to 58% for the standard palpation technique.^[7]

Slide preparation

Two slides should be available for each pass, for a total of 6 slides. After the first pass is collected, a small sample (ie, the size of a pea) is expelled onto the middle of one of the two slides for the first pass. Immediately after placing the specimen onto the slide, the corresponding slide is inverted over the first, and gentle pressure is applied. The slides are separated by pulling the slides in opposite directions.

Both slides are then sprayed with fixative or allowed to air dry. The needle is then rinsed into a small specimen container with CytoLyt.

The procedure is then repeated for passes 2 and 3. The 6 slides are then sent to pathology, along with the specimen container with CytoLyt.

Postprocedure monitoring

Patients should be kept seated and observed for several minutes following the procedure. There are no specific restrictions following a FNA. Patients can resume a normal diet and regular activities.

Common CPT codes

76536 - Ultrasonography, soft tissues of head and neck (eg, thyroid, parathyroid, parotid), real time with image documentation

76942 - Ultrasonographic guidance for needle placement (eg, biopsy, aspiration, injection, localization device), imaging supervision and interpretation

10022 - Fine-needle aspiration, with imaging guidance

No long-term monitoring is necessary.

Syncope

Some patients experience a near-syncopal or syncopal episode prior to, during, or after the procedure. The etiology is usually vasovagal syncope due to anxiety about the procedure. Patients should be laid down until they recover consciousness. A drink of water or cold compress can also help with symptoms.

Bleeding

Minor hematomas are the most common complication following FNA.^[9] Superficial skin bleeding can be controlled with local pressure. Patients should be kept in the office until all bleeding has stopped. Patients on anticoagulation may require a pressure dressing to control bleeding. This can be accomplished by using a 2x2 gauze and 2-inch silk tape.

Injury to a neck vessel such as the anterior jugular vein can lead to deeper bleeding and even a neck hematoma. If such an injury is suspected, local pressure should be applied for 10-15 minutes. Once pressure is released, if blood continues to accumulate, the physician can make a small incision adjacent to the needle puncture to localize the source of bleeding. Small vessels can be cauterized or suture ligated. If bleeding is brisk or the proper equipment is unavailable, the patient should be taken to the operating room for bleeding control. Any patient with an expanding hematoma and risk of airway compromise should have their neck opened and the blood evacuated emergently.