Thyroid nodule ablation is an interventional radiological technique to treat symptomatic solid and cystic thyroid nodules.

History

Ablation techniques for thyroid nodules have been widely adopted as first-line treatment options, particularly over the past 10-20 years, thanks largely to the pioneering work of the Korean Society of Thyroid Radiology. Both thermal and chemical ablation techniques are supported by level 1 evidence and have lower rates of complications and faster recovery than surgical options. Thermal (radiofrequency or microwave) ablation is most efficacious for solid or predominantly solid thyroid nodules, whereas ethanol (chemical) ablation is most efficacious for cystic or predominantly cystic thyroid nodules ^1-3.

Simple aspiration of cystic thyroid nodules has been performed since the 1960s; however, the application of this technique has been hindered by high recurrence rates. Better outcomes and long-term results are achieved with ethanol (chemical) ablation, with a therapeutic success rate of over 90% for cystic thyroid nodules. Ethanol ablation is now the first-line treatment for symptomatic cystic thyroid nodules ¹.

Since first performed and pioneered by radiologists in Korea over two decades ago ⁴, radiofrequency ablation (RFA) has become an established primary treatment for benign symptomatic solid thyroid nodules based on prospective randomised trials. It has been incorporated into major societal treatment guidelines ². RFA typically demonstrates superior outcomes based on patient satisfaction and quality of life scores and has lower complication rates and shorter length of hospital stay compared to surgical alternatives ^2-3. Microwave ablation (MWA) is an alternative technique with demonstrated efficacy and safety, and is commonly used in some practices.

Thyroid nodule ablation has shown good outcomes in the treatment of focal recurrence of post-resection thyroid cancer, where repeat surgery is challenging or contraindicated due to scarring and disruption of tissue planes ⁵. There is also emerging evidence supporting the efficacy of ablation techniques as a primary treatment option for small focal thyroid cancers ⁶.

Indications

• symptomatic nodule, e.g. discomfort, foreign body sensation, swallowing discomfort, cosmetic (e.g. visible neck mass) ^2,3

• sufficiently large to cause symptoms (commonly >2 cm) in size ^2,3

  • maximum size is not established, however, nodules ≥20 mL more commonly require multiple ablation sessions to achieve the goals of treatment

• TIRADS 1-4 score ^2,3

• Benign cytology on two fine needle aspiration (FNA)

  • in the case of predominantly cystic nodules, FNA is performed of the solid component ^2,3

  • single benign cytology sample is sufficient for nodules with highly specific benign ultrasound features (e.g., spongiform, cystic) ^2,3

Contraindications

• indeterminate or malignant cytology ^2,3

• extensive retrosternal extension (relative contraindication) ^2,3

• uncorrectable severe coagulopathy ^2,3

• pregnancy^{^}

• cardiac pacing devices^{^}

^{^}bipolar electrodes should be used in preference to monopolar electrodes ^2,3

Procedure

Preprocedural evaluation

Patients being considered for ablation techniques to treat symptomatic thyroid nodules should undergo an outpatient review by the treating interventional radiologist covering ^2,3:

• comprehensive symptom assessment and clinical examination

• imaging and biochemical assessment (e.g. ultrasound, TI-RADS, TSH, T3/4)

• FNA (two benign samples)

• coagulation studies

• treatment indications

• expectations

• other treatment options (conservative, surgical resection)

• informed consent

• direct in-office ultrasound examination by the treating interventional radiologist to identify critical anatomical structures, assess the target nodule’s characteristics, and plan a safe ablation treatment approach

Technique

Ethanol ablation

1. Skin sterilisation and local anaesthetic to the skin puncture site.

2. 16 or 18 G needle inserted into the cystic nodule under US guidance with a trans-isthmic approach.

3. Cyst fluid aspirated and debris removed as much as possible with saline irrigation.

4. Injection of 96% ethanol at ~50% of the aspirated volume up to a maximum total of 10 mL.

5. Ethanol left to dwell for at least 2 minutes before aspiration.

6. Monitor for pain and perithyroidal leakage.

Thermal ablation (RFA or MWA)

1. Skin sterilisation and local anaesthetic to the skin puncture site and perithyroid tissue.

2. Consider hydrodissection technique with 5% dextrose if required.

3. Thermal ablation electrode needle (commonly 17 or 18 G) inserted into the solid nodule under US guidance with a trans-isthmic approach.

4. Ablation performed using a "moving shot" dynamic approach ⁹.

5. The nodule should appear hypoechoic and devascularised at completion.

6. Monitor for pain, haematoma and skin burn.

Postprocedural care

Patients are typically monitored in a day-procedure ward for up to 4 hours post ablation treatment. After discharge, follow up is commonly arranged at 3, 6 and 12 months post-treatment with clinical, ultrasound and biochemical (if required) assessment in the outpatient clinic, depending on local practice guidelines and standards ^2,3.

Complications

Overall, ablation procedures for thyroid nodules have very low rates of complications, much lower than surgical alternatives (i.e. total or partial thyroidectomy) ^2,3,7,8:

• local pain and discomfort, skin burn, haematoma

• nerve injury (recurrent laryngeal, vagus, and sympathetic ganglion)

• nodule rupture

Hypothyroidism requiring long-term thyroxine medication post thyroid nodule RFA is exceptionally rare, but is typical after total thyroidectomy and relatively common (15-30%) after hemithyroidectomy ⁸.

Outcomes

Cystic and predominantly cystic nodules (ethanol ablation)

• significant improvement in pressure symptoms or cosmetic concerns in 95% ¹

• nodule volume reduction of ~75% (range 60–90%) ¹

• ethanol ablation is less effective in predominantly cystic nodules with a solid component of >20% ¹

Solid and predominantly solid nodules (thermal ablation)

• significant improvement in pressure symptoms or cosmetic concerns in 90% ^2,3

• nodule volume reduction of ~70% ^2,3

• <10% of nodules demonstrate significant regrowth at 3 year follow up ^2,3