Introduction: The thyroid sits in a pocket surrounded by multiple important structures including the trachea, recurrent laryngeal nerve (RLN) and vagus nerve, and common carotid artery. Unanticipated heat transmission outside the nodule parenchyma during thyroid ablative procedures has the potential to cause significant morbidity. In this brief video presentation, I discuss basic principles of laryngeal nerve and tracheal safety during radiofrequency ablation (RFA).

Materials and Methods: Anatomy of the RLN throughout its cervical course and the concept of the danger triangle versus danger zone for RLN safety during nodule ablation are discussed, in addition to vagus nerve anatomic variations. Useful procedural techniques to decrease the risk of nerve and tracheal injury during ablation are highlighted.

Results: Risk of injury to laryngeal nerves depends on their proximity to the thyroid capsule. In the lower neck, the right RLN runs in a lateral to medial direction as it ascends to enter the larynx, and anatomical studies have shown that the right nerve can be 2.5 cm or more from the right lateral wall of the esophagus in the lower neck.¹ The RLNs are most vulnerable to injury where they lie closest to the thyroid capsule, which occurs posteromedially at the level of the cricoid cartilage/first tracheal ring. This is the site of the so-called danger triangle where excessive ablation of posteromedial thyroid tissue could place the nerve at particular risk of injury.² However, many thyroid nodules extend to the lower neck and, at below the mid-cervical trachea, the concept of the “danger triangle” for RLN safety becomes less reliable, particularly on the right side. Instead, at these lower cervical levels, the entire posterior capsule should be considered a danger zone.³ Thyroid nodules generally abut at least one critical neck structure and great care must be taken to minimize heat transmission outside of the nodule parenchyma. Hydrodissection is one particularly important technique in this regard and is particularly useful for displacing carotid sheath structures laterally and skin anteriorly. Hydrodissection has less utility posteriorly within the RLN danger zone where other preventative procedural techniques can be utilized. Although local anesthetics agents are useful for hydrodissection, 5% dextrose is also beneficial in some locations. The internal mucosa of the trachea contains many sensory receptors and excessive heat transmission through the tracheal wall can cause pain protective reflexes such as cough to be triggered. As such, use of a nonconductive fluid (5% dextrose) without anesthetic properties when hydrodissecting the tracheal plane can safeguard against inadvertent heat transmission to the airway by allowing the patients to retain their airway sensation, and ability to feel pain and/or cough should irritation occur. Power, active tip size, and individual nodule parenchymal characteristics all determine the size of the ablation zone achieved.

Conclusion: RFA is a safe and effective technique, provided appropriate pre- and periprocedure precautions are taken. Extensive experience in neck ultrasound is mandatory to allow for appropriate preprocedural and periprocedural evaluation of individual anatomy.

The author has had no commercial associations during the past 2 years that might create a conflict of interest in connection with the video.

Runtime of video: 8 mins 43 secs