Ablation of Thyroid Nodules with Radiofrequency (RFA): questions and answers

ABLAZIONE DEI NODULI TIROIDEI CON RADIOFREQUENZA (RFA): DOMANDE E RISPOSTE

Thyroid nodules are abnormal enlargements, almost always benign in nature, that can occur in the thyroid gland, located on the front of the larynx and trachea. About 95% of nodules are benign in nature, only about 5% are malignant. Among the latter the most frequent (70-80%) are the papillary thyroid microcarcinomas. Dr. Roberto Valcavi, expert in Endocrinology and Interventional Thyroidology, Director of the ETC Clinic of Reggio Emilia, Italy, explains how benign nodules and malignant microcarcinomas can be destroyed with radiofrequency thermal ablation thus avoiding open surgery and the sacrifice of part of the thyroid (thyroid lobectomy) or of the entire thyroid gland (total thyroidectomy).

INSIGHT

1) What is Radiofrequency Ablation (RFA)?

Radiofrequency thermal ablation is an outpatient procedure that is carried out under ultrasound guidance, without the need to make surgical incisions. By means of a needle-electrode overheating nodular tissue, the volume of benign thyroid nodules is reduced by at least 80%. The reduction in volume of the nodule is generally sufficient to make the compressive symptoms disappear and obtain excellent aesthetic results. RFA improves the quality of life (Helath Related Quality of Life, HRQoL) [1, 2]. Micropapillary cancers disappear (90 -100%) after RFA procedure.

2) When RFA is indicated?

Radiofrequency thermal ablation is indicated for the treatment of solid or partially cystic benign nodules of the thyroid gland. Also in Autonomuously Functioning Thyroid Adenomas (AFTN) RFA obtains good outcomes.

Before RFA surgery, it is necessary to determine the nature of the thyroid nodule by ultrasound-guided fine needle aspiration biopsy (FNAB) and/or by needle biopsy with core needle (Core Needle Biopsy, CNB).

The best results are obtained on nodules of volume < 30 ml, oval shaped and colloid-cystic spongiform ecostructure. RFA is increasingly used for the ablation of micropapillary malignant tumors (microPTC) or lymph node metastases not responsive to radioiodine nor eligible for surgery (3, 4)

3) How is radiofrequency ablation performed?

The most commonly used technique is monopolar radio frequency. During surgery, the patient is part of a circuit that includes a radio frequency generator, a needle electrode and two dispersion plates placed on the patient’s legs (Fig 1). In bipolar radiofrequency the circuit opens and closes on the tip of the needle without passing through the patient’s body. It produces reduced ablations and should be reserved for patients with pacemakers or implanted defibrillators.

The needle electrode is introduced into the nodule under ultrasound guidance. The high frequency electromagnetic waves emitted by the electrode overheat the nodule inducing necrosis of the treated tissue, that will be replaced over time by fibrous-scar tissue. This results in a significant shrinkage of the thyroid nodule. A saline cooling system controls the temperature at the tip of the needle during treatment to avoid the carbonization process.

The procedure is performed on an outpatient basis, without the need for general anaesthesia with intubation. The patient is placed on the bed in a supine position, head hyperextended. The operator administers ultrasound-guided local anaesthesia with lidocaine at 2% (short action) and ropivacaine at 10% (protracted action). The anesthesiologist canulates a vein and sedates the patient with Fentanyl, Midazolam 3-5 mg, followed by low dose Propofol pump infusion.

Oxygenation is maintained by means of “goggles” connected to oxygen cylinder. Vital signs, including respiration, ECG, partial oxygen pressure, and blood pressure, are monitored by the anesthesiologist for the duration of the surgery. Sedation is necessary to facilitate maneuvering and to reduce spontaneous swallowing. Sedation causes loss of consciousness and even anterograde amnesia. The patient loses any memory of the surgery and does not complain of any intraoperative pain while maintaining a certain reactivity.

The procedure, including set-up times, has a variable duration of about 30-120 minutes. It is repeatable on particularly large nodules or in cases of relapse. At the end of the procedure, a steroid and analgesic therapy is administered via the venous route. After the RFA surgery the patient is kept in observation in the recovery room for 1-2 hours. Finally, before discharge the patient undergoes an ultrasound thyroid check.

4 How are the vital structures of the neck spared in RFA minimally invasive surgery?

Thyroid nodules appear near neck structures that must be saved: common carotid artery, internal jugular vein, vagus nerve, brachial plexus, cervical sympathetic, trachea, recurrent laryngeal nerve, esophagus, muscle fascia and muscles. Ultrasound visualization under technologically advanced equipment allows saving these structures. The hydrodissection technique (separation of the recurrent laryngeal nerve from the thyroid nodule by cold glucosate solution +2 C infusion) minimizes the risk of recurrent laryngeal nerve dysfunction that moves the vocal cord.

5) Can radiofrequency thermoablation cause risks or side effects?

With appropriate technique, complications and side effects are of minimal relevance. They include:

  • Neck discomfort
  • Pain radiating to the jaw
  • Skin bruising
  • Pinpoint skin burn
  • Pericapsular or intranodular bleeding

Dysphonia (hoarse voice) usually transient, due to simple overheating of the recurrent laryngeal nerve, innervating the vocal cord. Infusion of cold glucosa solution +2 °C minimizes the risk. Very rarely voice change is permanent.

Hypo/hyperthyroidism/autoimmune thyroiditis: they are observed in 1% of cases, are usually transient, have as markers antithyroid antibodies that are periodically checked in each patient.

6) Which is post-operative therapy?

At the time of discharge a post-operative ultrasound is performed, comparing the preoperative images with the post-operative ones. The patient is issued a discharge letter that briefly describes the RFA intervention and the outcome.

Some drugs are prescribed to patients:

  • Corticosteroids in various dose and duration to reduce postoperative edema and to prevent late colliquation, to be taken for breakfast
  • A pump inhibitor (lansoprazole) to be taken on an empty stomach in the morning with water 1 hour before breakfast to obtain gastroprotection, for the duration of corticosteroid treatment.
  • Antalgic (paracetamol 1 g) or antiinflammatory drugs (ketoprofen, ibuprofen, etc.) are administered in rare cases of late pain.

7) What are the advantages of minimally invasive and ultrasound-guided thermal-ablative surgery over traditional surgery?

Traditional surgery consists of lobectomy or total thyroidectomy; transaxillary or transoral robotic surgical variants have been proposed. Minimally invasive video assisted surgery, MIVAT (Minimally Invasive Video Assisted Thyroidectomy), is also practiced. Any surgery involves a skin cut and a hospital stay. Most importantly it involves the sacrifice of a thyroid lobe or the entire thyroid.

The advantages of ultrasound-guided radiofrequency ablation are:

  • No scars
  • Preservation of the thyroid gland
  • Saving the normal function of the thyroid gland.
  • No need to take any substitution therapy with thyroxine
  • Minimal side effects
  • Absence of general anesthesia, drainage tubes, hospitalization
  • Fast recovery to routine labor activities
  • The ablation results in an average mass reduction of 80% already in the first year, but the effects are remarkable already in the third month. With the passage of time the ablated mass is further reduced
  • The equivalence of surgical therapy and thermo-ablative therapy has been demonstrated
  • Minimized aggression
  • Improving the quality of life

Fig 1. Monopolar radiofrequency circuit. The generator (top left) produces an electric current that causes overheating on the tip of the needle-electrode (top right) inserted into the thyroid gland under ultrasound guidance. Internally, the needle is cooled by sterile saline at 2 C by a peristaltic pump (top center).

This prevents overheating of the needle-electrode tip and charring of the thyroid tissue. The active electrode needle tip is usually 1 cm, but fixed active tips of varying length or variable length can be used. The electric current focuses on the tip of the needle-electrode according to the physical principle of the dispersing power of the tips.

The circuit is closed by the dispersion plates attached to the front side of the thighs previously subjected to accurate trichotomy (shaving). The electrode needle performs the single ablation of a 1 cm sphere of tissue around the tip and must then be moved to form coalescent (fused) ablation spheres progressively. Under ultrasound guidance in real time, with delicate manouvers, the entire nodule is totally ablated.

REFERENCES

1) Roberto Valcavi, Petros Tsamatropoulos. Health-Related Quality of Life after Percutaneous Radiofrequency Ablation of Cold, Solid, Benign Thyroid Nodules: a 2 Year Follow-up Study in 40 Patients. Endocr Pract. 2015 Aug;21(8):887-96. doi: 10.4158/EP15676.OR. Epub 2015 Jun 29.

2) Mark A Lupo. Radiofrequency Ablation for Benign Thyroid Nodules-A Look Towards the Future of Interventional Thyroidology. Endocr Pract. 2015 Aug;21(8):972-4. doi: 10.4158/EP15797.CO. PMID: 26121459 DOI: 10.4158/EP15676.OR

3)Kim JH, Baek JH, Lim HK, Ahn HS, Baek SM, Choi YJ, Choi YJ, Chung SR, Ha EJ, Hahn SY, Jung SL, Kim SJ, Kim YK, Lee JH, Lee KH, Lee YH, Park JS, Park Guideline Committee for the Korean Society of Thyroid Radiology (KSThR) and Korean Society of Radiology. 2017 Thyroid Radiofrequency Ablation Guideline: Korean Society of Thyroid Radiology. Korean J Radiol. 2018 Jul-Aug;19(4):632-655. doi: 10.3348/kjr.2018.19.4.632. Epub 2018 Jun 14. PMID: 29962870

4) Lisa A. Orloff MD, Julia E. Noel MD, Brendan C. Stack Jr MD, Marika D. Russell MD, Peter Angelos MD, PhD, Jung Hwan Baek MD, PhD, Kevin T. Brumund MD, Feng-Yu Chiang MD, Mary Beth Cunnane MD, Louise Davies MD, Andrea Frasoldati MD, Anne Y. Feng BS, Laszlo Hegedüs MD, Ayaka J. Iwata MD, Emad Kandil MD, Jennifer Kuo MD, Celestino Lombardi MD, Mark Lupo MD, Ana Luiza Maia MD, PhD, Bryan McIver MD, PhD, Dong Gyu Na MD, PhD, Roberto Novizio MD, Enrico Papini MD, Kepal N. Patel MD, Leonardo Rangel MD, Jonathon O. Russell MD, Jennifer Shin MD, Maisie Shindo MD, David C. Shonka Jr MD, Amanda S. Karcioglu MD, Catherine Sinclair MD, Michael Singer MD, Stefano Spiezia MD, Jose Higino Steck MD, PhD, David Steward MD, Kyung Tae MD, PhD, Neil Tolley MD, Roberto Valcavi MD, Ralph P. Tufano MD,R. Michael Tuttle MD, Erivelto Volpi MD, PhD, Che Wei Wu MD, PhD, Amr H. Abdelhamid Ahmed MBBCH, Gregory W. Randolph MD

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Thyroid nodules are abnormal enlargements, almost always benign in nature, which can arise in the thyroid gland, located on the front of the larynx and