الفهرس 
Acknowledgements
ANATOMY OF THE THYROID GLANDOnly 14 pages are availabe for public view
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Abstract
Summary and Conclusion
Thyroid nodules constitute a frequently seen clinical problem, and the incidence of thyroid nodules has increased with the recently increased use of thyroid ultrasonography (US).
Thyroid nodules are common, their prevalence being largely dependent on the identification method. The estimated prevalence by palpation alone ranges from 4% to 7%, whereas US detects nodules in 20% to 76% of the adult population, particularly with the current use of high-resolution US techniques. The reported frequencies detected by US correlate with the prevalence reported at surgery and autopsy with ranges between 50% and 65% .
Increasing age, female gender, iodine deficiency, and a history of head and neck radiation seem to increase the risk of thyroid nodules .
Thyroid nodules are clinically important for several reasons. They may cause thyroid dysfunction and, rarely, compressive symptoms, but they are primarily important because of the need to exclude thyroid cancer. The reported prevalence of malignancy in thyroid nodules evaluated by biopsy ranges from 4.0% to 6.5% and is largely independent of the nodule size. Despite this, papillary microcarcinomas (smaller than 1 cm) incidentally found at the time of surgery are much more common (up to 36%), but it is controversial whether or not a survival benefit exists with the diagnosis and treatment of such entities, given their generally benign course.
Although most thyroid nodules are benign and do not require treatment, some benign nodules may require tretment for associated symptoms and/or because of cosmetic problems.
Radiofrequency ablation is a minimally invasive technique that can produce tissue coagulation necrosis in humans. This technique is performed effectively and safely with ultrasound or computed tomography guidance. It can be used to treat a variety of lesions in different organs, including benign and malignant diseases.
reporting the initial experience for ablation in metastatic lymph nodes from papillary thyroid cancer. More recently, radiofrequency ablation has also been shown to relieve compressive symptoms and cosmetic problems caused by benign thyroid nodules. Complications are not evident in benign thyroid nodules and recurrent thyroid cancer.
Radiofrequency (RF) ablation has been gaining popularity as a minimally invasive treatment in patients with benign thyroid nodules and recurrent thyroid cancers.
Radiofrequency ablation is a technique to destroy tissues with heat generated from high-frequency alternating current. The alternating current is created by a radiofrequency generator. The electrode and grounding pads are both connected to the generator, with the electrode inserted into the ablation target and grounding pads attached to the body surface, mostly at both thighs. In that way, the electrical conducting circle is formed. When the generator is powered on, the alternating electric current oscillating between 200 kHz and 1200 kHz in the electrode causes nearby tissue ion agitation, which can create frictional heat. With that heat, the electrode can cause target tissue coagulation necrosis. The grounding pads are large dispersive electrodes that can let the current go through the patient without causing significant heat as in the electrode tip. For complete target tissue coagulation, a higher temperature generated in the electrode needs less time to create sufficient necrosis. When the temperature is between 60 °C and 100 °C, tissue coagulation is noted almost immediately. When the temperatures fall between 50 °C and 52 °C, it takes 4–6 minutes to create irreversible cellular damage. If the temperature is just 46 °C, >1 hour is necessary to ablate the tissue successfully.
In conclusion, radiofrequency ablation has been shown to be a safe treatment of nodular thyroid diseases. Hospital admission is unnecessary. It also does not leave a scar in the neck. It can effectively reduce the volume of benign thyroid nodules. When a patient has well-differentiated thyroid cancer, radiofrequency ablation can also be an alternative treatment choice for those who are unable to receive surgical therapy.
RF ablation is a safe and effective alternative to surgery for treating benign, nonfunctioning, or autonomously functioning nodules as well as for recurrent thyroid cancers.
Its efficacy can be maximized by complete ablation of the entire tumor margin, which is essential in order to prevent marginal regrowth and to effectively reduce the size of thyroid nodules. And in order to minimize the possibility of complications, it is important to consider the broad spectrum of possible complications as well as the available preventative techniques.
Future Perspectives
In the future, RF ablation could be a promising minimally invasive technique for the treatment of benign thyroid nodules and recurrent thyroid cancers. RF ablation could also be used for inoperable patients with primary thyroid cancers. For safe and effective RF ablation, the operators should be aware of the US anatomy of critical structures in the neck as well as various techniques and devices used for thyroid RF ablation.
Although esophageal or tracheal injury, heart problems caused by the RF current, and thermal injury to critical structures in the neck such as the cervical sympathetic nerve and spinal accessory nerve have not been reported, the operator should be aware of the significance of such possible complications, especially when a recurrent tumor is close to neck nerves. In order to prevent thermal injury to critical structures, injection of fluid between the target tumor and critical structures has been suggested. This technique is also useful when treating recurrent thyroid cancers. For the treatment of recurrent thyroid cancers of the neck, the use of a unidirectional ablation electrode has been suggested as this partially insulated electrode could modify the direction of the ablation zone and finally achieve a half-moon-shaped ablation zone rather than the round ablation zone usually made by a conventional electrode.
As the RF current passes through the heart during thyroid RF ablation, heart attacks and arrhythmias may be possible complications. In order to prevent cardiac problems caused by the RF current, a bipolar electrode could be used, although it is not yet available for use in the thyroid gland.
As suggested for the treatment of liver tumors, a wet, internally cooled electrode may prevent carbonization and could thus enhance the ablation zone. In the treatment of thyroid tumors, a wet electrode may increase size of the ablation zone and reduce the ablation time. The combination of ethanol and the RF ablation technique has been used for treating liver and thyroid tumors as ethanol can increase the size of the ablation zone and also prevent carbonization during RF ablation. Therefore, a combination of ethanol and RF ablation can be considered as the one of the successful treatment options for thyroid nodules.