Percutaneous Ultrasound- Assisted Radiofrequency Ablation (RFA) of Cold Benign Solid Thyroid Nodules
Percutaneous Ultrasound-Assisted Radiofrequency (RFA) of Cold Benign Solid Thyroid Nodules: during the last few years, several papers demonstrated the effectiveness of ultrasound assisted percutaneous Radiofrequency Ablation (RFA) of cold solid benign thyroid nodules.
The procedure is carried out on outpatients. With no surgical scar, as a needle is used, RFA may reduce by 50%- 85% the volume of a benign thyroid mass in a single session. The efficacy of volume shrinkage is related to the amount of nodular tissue ablated (destroyed) by the procedure. Other factors (nodule shape, echostructure, intrinsic tendency to grow) may also influence the clinical outcome. The shrinkage obtained by RFA is generally sufficient to eliminate or, at least, to better compressive symptoms and cosmetic discomfort, hence improving the health-related quality of life.
Thyroid nodules are close to vital structures, common carotid artery, internal jugular vein, vagus nerve, trachea, laryngeal recurrent nerve, brachial plexus, esophagus, muscles and strap muscles. In order to save these structures, RFA must leave behind some viable tissue around them. Therefore, over the years, it could happen re-growth of the nodule and treatment repeated.
Indications and limits of RFA treatment
Indication of the RFA procedure is the treatment of solid or partially solid cold benign thyroid nodules in patients at poor surgical risk or in patients who refuse surgery. Benignity must be demonstrated by cytology obtained through ultrasound-guided Fine Needle Aspiration (FNA) and/or by Core Needle Biopsy (CNB). FNA should be repeated at least twice, the last time within 6 months the RFA intervention.
Best results are obtained in regularly shaped ellipsoid nodules, with a spongiform colloid-cystic structure. In selected cases warm or hot nodule could be treated. However in these cases the risk of recurrence is high. Limits of RFA are related to possible re-growth of the ablated nodule. The alternative therapies are surgery or, in hot hyperfunctioning nodules, radioiodine (131-I) administration.
RFA thermal ablation
RFA is used since the end of 70’s for several organs, liver in the first instance. More recently its use has been extended to benign cold thyroid nodules. In selected cases it has been used also for malignancy. In the monopolar RFA technique, the patient is part of an electric circuit including a RF generator, an electrode-needle and dispersing ground pads usually fit on patient’s legs. The radiofrequency electrode needle concentrates energy, heating the tissue through ionic friction.
The electrode needle is introduced within the nodule through a trans-isthmic approach under real time Ultrasound (US) imaging. The electrode needle heating of the tissue produces coagulative necrosis of the nodular tissue which will shrink over time due to fibrotic retraction. The shrinkage process takes over in about few weeks following the initial inflammation due to burn. The electrode needle is internally cooled by a cold saline solution thus preventing tissue carbonization. The needle is fit at the deepest layer, than is retracted when an hyperechoich signal due to bubbles of gas and an abrupt increase in impedance indicate that the treated nodule portion is dissiccated. The electrode needle is then repositioned in other tracks, until the maximum nodular tissue has been exposed to RFA.
The RFA intervention is on fasting outpatients. No general anesthesia is needed. The patient lay on the operatory bed in supine position, with hyper-extended neck. Conscious sedation is obtained through i.v. midazolam administration. Sedation is used as it favors maneuvers, improves tolerance and reduces spontaneous swallowing. The operator works in a sterile field with sterile instruments.
After superficial and pericapsular anesthesia with 2% ropivacaine, the electrode needle is inserted inside the thyroid nodule. The procedure, including preparation time, may have a duration variable between 30-60 min’. It is repeatable in particularly bulky nodules or in case of recurrence. All maneuvers, including local anesthesia, are carried out under real-time US-imaging. At the end of procedure, steroid to reduce edema and pain killers, if needed, are administered. After RFA the patient is kept under observation for 1-2 hours and checked with a final US examination. The day after, the patient has another check with US.
Outpatients must be accompanied and avoid to drive after RFA.
Tolerability and side effects
As a rule RFA procedure is well tolerated. Immediately after RFA and in the following 7-10 days, some tenderness is seldom reported. Rarely fever (38-38.5 °C) may appear. Corticosteroid administration in a short course of 6-10 days after procedure minimize all these discomfort. Infrequent side effects may include effusion due to pericapsular hematoma, cutaneous burn, nodule liquefaction, tumor rupture with fasciitis, vagal reaction. Vocal change due to laryngeal nerve injury is rare.
In benign cold nodule RFA, thyroid hormone levels do not significantly change. In patients with pre-existing chronic thyroiditis, change in anti-thyroid antibodies may be associated with hyper or hypothyroidism. This is a very rare unpredictable reaction.
Percutaneous ultrasound assisted RFA is a new therapeutic approach that may reduce surgery for benign cold thyroid nodules.