Thermal ablation of thyroid nodules as an alternative treatment option for thyroid surgery
In addition to enlargements, thyroid nodules are counted among the most common alterations of the thyroid gland. In Germany, these nodules are mostly benign, carcinomas of the thyroid gland average only 0.1-1% of all malignant diseases. Thermal ablation techniques, which have already been used successfully for treatment of liver, lung and kidney, can also be used for treatment of thyroid nodules.
What is thermal ablation?
Thermal ablation is an umbrella term for various thermal techniques which destroy tissue through heat. This includes Radiofrequency Ablation (RFA), High Frequency Focused Ultrasound (HIFU), Laser Induced Thermo Therapy (LITT) and Microwave Ablation (MWA). With these non-surgical methods, heat is generated directly inside the thyroid nodule. When temperatures rise above 42 °C, temperature-induced cell damages occur. As temperatures exceed 60 °C these cell damages get irreversible; i.e. the treated thyroid tissue, which forms the hot and/or cold nodule, is removed by the body’s defense system. The nodule gets considerably smaller over time.
Which techniques are suitable for thermal ablation of thyroid nodules?
Currently, Radiofrequency Ablation presents the best studied and most frequently used technique. Current flow is generated at the tip of the RFA probe, an electrical field is created and tissue is heated. Safety and efficiency of RFA as a treatment option for thyroid nodules could be shown in over 100 studies. Therefore, in some countries Radiofrequency Ablation is counted among recommended methods for therapy of benign thyroid nodules and local recurrences of thyroid carcinomas.
For Laser Ablation, Microwave Ablation and HIFU, less studies are reported. However, results for LITT and MWA are comparable to those for RFA. Data about HIFU of thyroid nodules can rarely be found.
Concerning Laser Ablation, the light of specific wavelengths is emitted into the tissue and, due to light- (photon-) absorption, temperatures up to 300 °C are created. Therefore, general anesthesia is needed in most cases. In view of Microwave Ablation, microwaves are generated at the tip of the probe and water molecules are stimulated by the electromagnetic field that is created. This stimulation generates heat.
How is thermal ablation performed?
The technical implementation of thermal ablation techniques is easy and does only require local anaesthesia. After an analgesic injection and skin disinfection, an ultrasound-guided needle will be placed minimal-invasively inside the thyroid nodule. The needle (or probe) will be activated for several minutes, heat is generated in the area of the nodule. The treatment can be finished if the nodules have shrunk, otherwise it will be repeated. Thermal ablation by means of HIFU is performed without any kind of needle. Ultrasound waves are focused inside the thyroid nodules through a special concave (inwardly curved) ultrasound probe and generate heat.
What are the chances of success for thermal ablation of thyroid nodules?
Latest studies show that volume reduces by an average of 30-50 % after three months; after six months the reduced nodule volume is already 40-65 %. Nodule volume is reduced by up to 50-90 % in long term follow-up periods of 12 months. The percental volume reduction is dependent on the nodule character. Thyroid nodules can be divided in three groups: solid, complex and cystic; cystic nodules show the best results when compared to other categories.
What are benefits of thermal ablation of thyroid nodules?
- minimal invasive (RFA, MWA) or even non-invasive (HIFU)
- is performed with local anesthesia (except laser ablation)
- can be performed on an out-patient basis
- risk of development of scars is marginal
- success rates are promising
What are possible complications?
Complication rates are comparable to those of thyroid surgeries, whereas remaining complications, such as vocal cord paralysis, are less common. Other possible side effects are infections and so-called method-dependent complications such as tissue damages in the area of the insertion channel. However, such complications are really rare.