**7. Anatomical tips for TOVS in hypopharyngeal cancer**

The tips of the inside-out anatomy of the larynx and hypopharynx are shown in **Figure 5a**. The superior laryngeal artery and superior laryngeal nerve enter the laryngopharynx through the thyrohyoid membrane. The superior laryngeal nerve runs along the submucosal layer of the anterior wall of the pyriform sinus. The recurrent laryngeal nerve runs in a deep layer between the inferior cornu of the thyroid cartilage and the posterior cricoarytenoid muscle. The superficial branch of the recurrent laryngeal nerve usually causes anastomosis with the superficial laryngeal nerve (Galen's anastomosis).

#### **Figure 5.**

*Inside-out anatomy of the larynx and hypopharynx. a. Landmarks of the larynx and hypopharynx. b. Location of the carotid artery after surgical field exposure. a. Artery, n. nerve.*

#### *Transoral Videolaryngoscopic Surgery (TOVS) DOI: http://dx.doi.org/10.5772/intechopen.97473*

The carotid artery is close to the surgical field in some cases of angiectopia. The carotid artery is also close to the surgical field in cases of excessive laryngopharyngeal suspension to better expose the surgical field. The retractor opens the space between the alar of the thyroid cartilage and the prevertebral space, which causes the shift of the carotid artery from lateral to medial. As a result, the carotid artery becomes adjacent to the area between the posterior wall and the outer wall of the piriform sinus behind the alar of the thyroid cartilage (**Figure 5b**). Therefore, especially in the case that includes the pharyngeal constrictor muscle layer resection, the procedure should be performed with careful caution. Since this cannot be predicted by preoperative imaging, it is necessary to estimate the position of the carotid artery by careful observation of the arterial pulsation in the endoscopic view and the shift of the pulsating site by manual compression from the outside of the neck.

In the case of deeper infiltration in the posterior wall, the resection should also be performed with careful caution. When an excision of all layers of the pharyngeal constrictor muscle is performed, deeper damage from the buccopharyngeal fascia to the alar fascia causes perforation of the danger space in the retropharyngeal space (**Figure 5a**). This damage may cause severe postoperative complications such as cervical spondylitis and/or mediastinitis. In particular, post-irradiated cases have a high risk of developing complications due to poor wound healing and increased susceptibility to infection. Therefore, it is important to preserve the buccopharyngeal fascia and alar fascia whenever possible.

To perform better and safer transoral surgery, the surgeon should understand and familiarize themselves with the anatomical landmarks inside the laryngopharynx, check the preoperative endoscopic and imaging findings, observe surgical fields in detail under videoscopic view, and manipulate a careful procedure for each case.
