Thyroid fine needle aspiration (FNA)

Authors: Prof Stacy Goergen*
                            Prof Rob Gibson *

What are the generally accepted indications for a thyroid FNA?

Thyroid nodule fine needle aspiration biopsy is generally carried out in the setting of a palpable nodule or ultrasound-detected thyroid nodule in order to confirm or exclude a malignant nodule. It is the most cost-effective initial method for guiding the clinical management of patients with thyroid nodules.
Palpable thyroid nodules are estimated to occur in 1% of males and 5% of females living in non-iodine deficient locations. Ultrasound evaluation of the thyroid reveals nodules in 16–67% of adults, women more commonly than men and the large majority are benign nodules[1]. Not all palpable nodules correspond with a discrete abnormality when the area is examined with ultrasound and, by definition, these are not considered thyroid nodules. On the other hand, nodules detected on ultrasound may not be clinically palpable, but may have the same malignant potential as palpable nodules of the same size and thus should be dealt with similarly. Certain characteristics of nodules detected with ultrasound increase the likelihood of the nodule being malignant.
The incidence of thyroid cancer is increasing. So-called ‘differentiated’ (papillary and follicular) cancers comprise up to 90% of all thyroid cancers. The chance of any given nodule being malignant depends on:

1. age and sex of the patient;
2. rapid nodule growth and/or hoarseness;
3. palpable fixation of the nodule to the surrounding tissues;
4. presence of accompanying cervical lymph node enlargement;
5. presence of a family history of thyroid cancer and/or multiple endocrine neoplasia type II or other syndromes:

•  Carney syndrome;
•  multiple polyposis coli;
•  Cowden syndrome;
•  Werner syndrome.
•  radiation exposure, especially during childhood and young adulthood.

Several characteristics of nodules on investigation influence the likelihood of thyroid malignancy:

An ultrasound-detected or clinically palpable nodule that is ‘hot’ (or shows increased uptake) on pertechnetate nuclear medicine thyroid scan is so unlikely to be a cancer that biopsy is not recommended [1]. However, care must be taken to ensure that the ‘hot’ area on the nuclear medicine scan corresponds to the ultrasound detected or clinically palpable lesion. This is not always straightforward, especially when multiple nodules are present, as is commonly the case, particularly in adult females who have lived for many years in an area where the soil is deficient in iodine.

The appearance of the nodule on ultrasound.

A number of ultrasound features suggest an increased likelihood that a given thyroid nodule is malignant and they include:

• microcalcification (macrocalcifications, by contrast, are common in benign nodules);
• irregular margins;
• “taller than wide” morphology (indicative of solid rather than fluid nature of the nodule);
• internal vascularity;
• enlarged cervical lymph nodes on the same side of the neck.
• The more of these features that seen, the more likely it is to be malignant.

Ultimately, the decision to perform FNA on any given nodule will be made based on a variety of clinical considerations including the results of other imaging as well as the sonographic appearance of lesion.

What are the prerequisites for having a thyroid FNA done?

The most recent guidelines from the American Thyroid Association [3] recommend that patients with a clinically suspected thyroid nodule receive:

• serum TSH measurement; or
• diagnostic thyroid ultrasound.

The serum TSH measurement is carried out for the following reasons:

• Depressed TSH should trigger a Technetium 99m radionuclide scan as it suggests local or global thyroid hyperfunctioning. If a sonographically-detected thyroid nodule corresponds to a ‘hot’ or hyperfunctioning on the radionuclide scan, the likelihood that it is malignant is negligible and thus fine needle aspiration is not indicated.

Thyroid ultrasound is carried out in order to:

• Confirm that a palpable abnormality does or does not represent a thyroid nodule; and
• Determine whether the nodule is isolated or part of a more generalised process, such as goitre or the generalised enlargement seen in Hashimoto’s thyroiditis.
• Other masses in the neck, such as lymph nodes, salivary gland enlargement, branchial cysts or, more rarely, thyroglossal duct cysts, can produce a palpable lump near the thyroid.
  (See Appendix 1)

What are the absolute contraindications for a thyroid FNA?

There are no absolute contraindications, as the needle used for this procedure is very small, but profound coagulopathy and inability of the patient to co-operate with the procedure (e.g. altered conscious state, dementia or communication difficulties of any kind) increase the risk of bleeding into the thyroid bed (see risks).

What are the relative contraindications for a thyroid FNA?

Thyroid FNA should be carried out as a targeted procedure on a lesion in the thyroid that has malignant potential, so lack of a focal abnormality is a relative contraindication to the procedure.
A known coagulation disorder (intrinsic or iatrogenic) can increase the risk of bleeding with this procedure. However, a recent systematic review by Polyzos [4] states that standard anticoagulation within an acceptable therapeutic range should not be a contraindication to FNA.
For patients taking antiplatelet or anticoagulant medication, provided it is considered medically safe to temporarily stop the medication, cessation is advisable before FNA. Radiology practice and hospital-specific policies exist regarding cessation of these medications.
The following parameters are recommended in order to minimise the risk of postprocedural haemorrhage in patients undergoing thyroid FNA:

• INR < 1.5
• Platelet count: generally >100,000

What are the adverse effects of a thyroid FNA?

This issue has been addressed in a recent systematic review. [5]

The major risks are bleeding and indeterminate biopsy result.

Blood extravasation related complications. This is more common in patients who have a lesion that is deep or when the lesion has a cystic component >50% of the whole lesion size. The review found extravasation occurred between 1.6 and 6.9% of all FNA procedures. The risk is a little higher with cystic compared with solid nodules. Just seven cases of life-threatening haemorrhage were reported in a series of over 17,000 FNA procedures.

The commonest manifestation of bleeding is local pain and tenderness, possibly mild dysphagia, and sometimes visible local swelling.

The risk of bleeding diminishes with:

• a few minutes of manual compression of the biopsy site immediately after needle withdrawal at the time of FNA with or without an ice pack;
• use of a small (25G ) needle;
• avoidance of any strenuous activity in the 24 hours after biopsy, particularly activities that could increase venous pressure in the neck, such as work overhead or exercise involving valsalva maneouvers.

Indeterminate result/inadequate specimen

This is unfortunately not uncommon, and complicates clinical management with regard to decisions about what to do next. Indeterminate results are less common when the FNA is performed by someone who does the procedure regularly and is experienced.The presence of a cytologist or cytology technologist can reduce the likelihood of an inadequate specimen by viewing it at the time of the procedure and informing the radiologist about whether or not another specimen is needed. This also has the potential to reduce bleeding complications by reducing the number of needle passes beyond what is required for a diagnosis.

Note that papillary cancers are diagnosed on the basis of features indicative of nuclear atypia in individual cells and thus can be diagnosed based on a good quality FNA specimen. Follicular cancers, on the other hand, are diagnosed based mainly on histological characteristics and thus specimens containing follicular cells may be cancer, adenoma or even a non-neoplastic colloid nodule within a goitre. Thus, when follicular cells are retrieved in an FNA, even when the amount of material is adequate, the result will be reported as indeterminate and either ultrasound follow up (to assess for growth), repeat FNA or removal of the nodule and/or hemithyroid will be needed depending on the level of clinical suspicion.

Other complications.

All of these occur more rarely than haemorrhage, but you should be aware of them in patients who have had FNA[3]:

• Acute or delayed diffuse thyroid swelling. Some cases have been treated with corticosteroids, but this tends to be self-limiting in 24–48 hours and, unlike massive thyroid haemorrhage, is not associated with airway compromise.
• Recurrent laryngeal nerve palsy. This is rare and tends to be self-limiting.
• Cervical radiculopathy. Uncertain whether this is a result of a reaction to local anaesthetic, haematoma-related compression or direct trauma.
• Post aspiration thyrotoxicosis. One study found this occurred in 1% of patients. The mechanism is unknown.
• Rare complications that are the subject of a few case reports include:
• Dysphagia (possibly a result of inadvertent oesophageal puncture), carotid artery subendothelial haematoma, development of a fibrovascular mass mimicking haemangioma and pseudoaneurysm formation.
• Needle track seeding with tumour. Is much rarer than with needle biopsy of abdominal malignancy and has been reported mainly with anaplastic tumours.
• Radioiodine used to treat thyroid cancer seems to be effective in treating needle track seeding.

Are there alternative imaging tests, interventions or surgical procedures to a thyroid FNA?

An open surgical biopsy is the alternative way to biopsy the thyroid

Further information about thyroid FNA:

The results of FNA are traditionally divided into:

• benign;
• malignant (>95% cancer risk at surgery);
• inadequate/insufficient material;
• indeterminate.

The addition of two more categories to this classification has recently been suggested [1]

Suspicious for malignancy (risk 50–75%).

Follicular lesion of undetermined significance (5–10% risk of malignancy).

It has also been suggested in this same guideline that the ‘indeterminate’ category be changed to: ‘neoplasm, either follicular or Hurtle cell (risk of malignancy 15–25%)’.

Mutation Testing

There is emerging evidence for the role of genetic testing of aspirated material for somatic mutations (e.g. BRAF) in reducing the rate of indeterminate FNA.
Between 15 and 30% of thyroid FNA results are inconclusive. Lesions that are more than 50% cystic on ultrasound or very small (<10mm) lesions are more likely to yield indeterminate results. Inconclusive results are also more likely with inexperienced operators.

Patients with indeterminate results or inadequate material should be considered for repeat FNA. The decision for repeat FNA should be influenced by the presence or absence of ultrasound signs suggesting malignancy as well as consultation with an endocrinologist and / or endocrine surgeon.

 Useful websites about thyroid FNA:

Suen KC. Fine-needle aspiration biopsy of the thyroid. Canadian Medical Association Journal, 2002. 167(5): p. 491–495:
http://www.cmaj.ca/content/167/5/491.full
Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer:
http://www.thyroid.org/professionals/publications/guidelines.html

References

Tan, G.H. and H. Gharib, Thyroid incidentalomas: management approaches to nonpalpable nodules discovered incidentally on thyroid imaging. Ann Intern Med, 1997. 126(3): p. 226-31.
Liu, Y.I., et al., A Bayesian Network for Differentiating Benign From Malignant Thyroid Nodules Using Sonographic and Demographic Features. American Journal of Roentgenology, 2011. 196(5): p. W598-W605.
Cooper, D.S., et al., Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer. Thyroid, 2009. 19(11): p. 1167-214.
Polyzos, S.A. and A.D. Anastasilakis, Clinical complications following thyroid fine-needle biopsy: a systematic review. Clin Endocrinol (Oxf), 2009. 71(2): p. 157-65.
Polyzos, S.A., et al., Epidemiologic analysis of thyroid fine needle aspiration biopsies over a period of 18 years (1987-2004). Exp Clin Endocrinol Diabetes, 2008. 116(8): p. 496-500.

*The author has no conflict of interest with this topic.

Page last modified on 30/8/2018.