All thermal ablation techniques depend on the destruction of tissue under extreme hyperthermic conditions. There are multiple thermal ablation techniques that differentiate from each other based on methods used and temperature differences.
Types of Thermal Ablation Techniques
An electrode tip having a combination of conduction and frictional heat is used to destroy the target tissue. The moving-shot technique is used for thyroid nodules to minimize the conductive effect.
- Laser Ablation
Laser ablation is another technique to deliver thermal energy and has been applied to thyroid nodules. In laser ablation, energy absorption is temperature-dependent and non-linear. As a result, it delivers less energy which may confer better control and safety in critical areas.
- Microwave Ablation
The microwave ablation technique depends on electromagnetic field and frequency generation to cause the oscillation of water, which produces friction and ultimately increases the local temperature. This technique is effective in large tumors and tissues that dessicate and impede electrical currents.
- High-Intensity Focused Ultrasound
HIFU is a non-invasive technique that uses sound waves to target specific tissue. High-intensity ultrasound transfers energy to induce cell destruction via mechanical and thermal injury.
- Alcohol (Ethanol) Ablation
Ethanol’s intratumoral administration was developed as a surgical alternative for hepatocellular carcinoma treatment. However, it has subsequently been applied across several malignant and benign pathologies. Ethanol ablation promotes tissue destruction using two methods. The first is cellular dehydration which leads to protein denaturation and coagulation necrosis induction. The second occurs when ethanol causes damage to the vascular endothelium, ultimately resulting in tissue ischemia.
Experts’ Recommendations For Ultrasound-Guided Ablation
- The US-guided ablation technique can be used on patients with benign thyroid nodules AFTNs and have contraindications to first-line techniques.
- The procedure is suitable for patients having primary papillary microcarcinoma who’re unfit or decline surgery.
- Patients with prior surgical history or voice impairment must be assessed for vocal fold mobility.
- Before the ablation procedure, a complete biochemical, radiographic, symptomatic, and medical evaluation should be performed.
- Hydro-dissection will be helpful to minimize patient discomfort and reduce unintended thermal spread.
- The moving-shot technique will significantly minimize thermal injury to critical structures.
- Patient-reported outcomes such as cosmetic, validated symptoms, and quality of life can be used to determine efficacy.
- For remnant nodular tissue which contributes to cosmetic or symptomatic concerns, consider repeat ablation of the benign nodule.
- For persistent hyperthyroidism, retreatment can be performed.
- Proficiency with UG-FNA biopsies is recommended to perform successful US-guided ablation.
A pre-procedural ultrasound is essential to evaluate the characteristics of target tissue in both malignant and benign diseases. Tumor dimensions or preoperative nodule and volume should be established to compare with follow-up exams. The proportion of cystic and solid components must be assessed to determine the best ablation technique. Vascularity should also be observed.
Informed consent is also necessary for the pre-procedural process. It’s the physician’s responsibility to set clear expectations during ablation. The physician should also evaluate the patient’s overall medical status and associated medications. Since ablation techniques are gaining popularity among practitioners and patients, the appropriate application of evidence-based techniques and principles should remain a top priority!
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Orloff LA, Noel JE, Stack BC Jr, Russell MD, Angelos P, Baek JH, Brumund KT, Chiang FY, Cunnane MB, Davies L, Frasoldati A, Feng AY, Hegedüs L, Iwata AJ, Kandil E, Kuo J, Lombardi C, Lupo M, Maia AL, McIver B, Na DG, Novizio R, Papini E, Patel KN, Rangel L, Russell JO, Shin J, Shindo M, Shonka DC Jr, Karcioglu AS, Sinclair C, Singer M, Spiezia S, Steck JH, Steward D, Tae K, Tolley N, Valcavi R, Tufano RP, Tuttle RM, Volpi E, Wu CW, Abdelhamid Ahmed AH, Randolph GW. Radiofrequency ablation and related ultrasound-guided ablation technologies for treatment of benign and malignant thyroid disease: An international multidisciplinary consensus statement of the American Head and Neck Society Endocrine Surgery Section with the Asia Pacific Society of Thyroid Surgery, Associazione Medici Endocrinologi, British Association of Endocrine and Thyroid Surgeons, European Thyroid Association, Italian Society of Endocrine Surgery Units, Korean Society of Thyroid Radiology, Latin American Thyroid Society, and Thyroid Nodules Therapies Association. Head Neck. 2022 Mar;44(3):633-660. doi: 10.1002/hed.26960. Epub 2021 Dec 23. PMID: 34939714.
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