2 Base of Tongue Resection and Hypopharyngeal Anatomy
Key Landmarks
Anterior and posterior tonsillar pillars
Extrinsic tongue musculature
Hyoglossus
Genioglossus
Styloglossus
Stylopharyngeus muscle
Hyoid
Epiglottis
Key Vascular Structures
Lingual artery
Internal carotid artery
Key Nervous Structures
Lingual nerve
Glossopharyngeal nerve
Hypoglossal nerve
Background
Base of tongue (BoT) resections for primary neoplasms using a transoral robotic surgery (TORS) approach were first described by O′Malley et al in 2006. 1 This approach evolved from a progression of techniques, trading efficacy of control of neoplasms for decreased morbidity. It was noted that the combination of minimally invasive resections with postoperative chemotherapy and radiation allowed good local and distant control with decreased morbidity.
Given the proximity of important structures such as the lingual artery and hypoglossal nerve, extensive knowledge of the expected anatomy, as well as the anatomy of the patient as defined in preoperative imaging, is paramount for reducing intraoperative complications as well as postoperative morbidity. The dissection will involve the BoT, the lingual tonsils, and possibly the palatine tonsils.
The hypopharynx may also be involved in BoT or tonsillar fossa tumors, as the divisions between the anatomical regions are not fascial planes but theoretical. Anatomy of the hypopharynx will also be discussed in this chapter. Fig. 2.1 highlights the axial, coronal, and sagittal anatomy of the tongue.
Indications
Although TORS was initially described in the literature for cancers or other lesions of the BoT, as surgical experience grows, there is also increasing data regarding its use for obstructive sleep apnea (OSA). 2 , 3 Primary indications include control and resection of neoplastic processes (typically squamous cell carcinoma) and excision of redundant and obstructive tissues to increase air passage in OSA. Surgical excision in the treatment of OSA may be minimized by performing a midline glossectomy only, minimizing the risk of damage to critical neurovascular structures. In contrast, a more radical excision may be necessary for neoplasms. The anatomical boundaries of the base of tongue are not necessarily well defined by fascial planes and are contiguous with nearby regions, such as the hypopharynx and tonsillar fossa. As well, minor salivary gland tumors of the tongue rarely arise on the midline and will likely require lateral resections. The primary contraindications for TORS BoT resections include severe trismus, which would preclude the use of instrumentation in the mouth; cancer with extensive distant metastases, extension into the skull base, bilateral base of tongue, or prevertebral fascia; involvement of the carotid sheath or artery; or involvement of more than half of the tongue base, as this would likely result in severe dysphagia.
Surgical Procedure and Anatomy
TORS BoT resection begins with proper exposure, including selection of the preferred retractor. The patient should be intubated nasally to minimize interference from the endotracheal tube. As described by Friedman et al, 3 , 4 in order to improve access to the oropharynx with the robotic instrumentation and cameras, a modified Z-palatoplasty (ZPP) may be performed. This procedure may also improve outcomes in BoT surgeries for OSA by reducing redundancy of tissue and increasing the distance between the palate and posterior pharyngeal wall. Briefly, the mucosa of the inferior portion of the soft palate is resected down to the musculature of the soft palate and uvula in a U-shape, with the nadir of the U over the uvula. The uvula and soft palate are split in the midline with cold steel, and the resultant flaps are reflected laterally and rotated anteriorly to expose the mucosa of the superior surface of the soft palate. This brings the mucosal edges together to be closed and opens the oropharynx ( Fig. 2.2a,b ).
Attention is then turned to the tongue, which is retracted forward with the help of sutures placed through the anterior portion, in order to avoid the lateral-lying vascular and nervous structures. The resulting view should be familiar to otolaryngologists, with the uvula and soft palate at the inferior portion of the viewing field, the palatine tonsils laterally, and tongue superiorly. Anteriorly, the oral tongue is divided from the BoT by the sulcus terminalis and foramen cecum. The epiglottis lies posteroinferiorly, with the vallecula found between the median and lateral glossoepiglottic folds. Laterally, the BoT is connected to the tonsillar fossa by the mucosa overlying the palatoglossus muscle. The midline sulcus of the tongue and the foramen cecum mark the divide between the left and right portions of the BoT.
BoT Resection for Neoplasm 1 , 2 , 5 , 6
Traditionally, tumor resection in the base of tongue is en bloc, with removal of a single specimen or a few specimens. This necessitates accurate knowledge of the typical anatomy of the region, as well as knowledge of patient-specific anatomy and characteristics of the tumor gained through physical examination, imaging, and possibly direct laryngoscopy. To familiarize the reader with the typical anatomy, this chapter will discuss a piecemeal dissection.
The robotic instrument is docked, and the anatomical borders of the BoT should be identified. If necessary, resection begins with removal of the palatine tonsils in the common fashion in the subcapsular plane in a manner similar to that described in Chapter 1 (medial to the superior pharyngeal constrictor). The mucosa and lingual tonsillar tissues of the BoT are then carefully removed from the tongue superficially posteroinferior to the sulcus terminalis. Immediately below this, a rich network of arterioles derived from the dorsal lingual arteries is encountered. This network should be removed with meticulous attention to hemostasis. In conjunction, following the branches laterally will enable identification of the lingual artery deep and lateral to the insertion of the palatoglossus muscle into the BoT. Branches can sometimes be seen running into the vallecula and onto the epiglottis ( Fig. 2.3 ).
Returning to the midline, further lymphoid tissue is also seen inferior to the arteriolar plexus and removed, exposing the intrinsic musculature of the tongue. The superior longitudinal muscle fibers can be identified in a thin plane down to the vallecula. Resection of these muscle fibers will reveal the intertwined fibers of the verticalis and transversus muscles, which contribute to the bulk of the tongue. Deep to these muscles, we see the inferior longitudinal muscle, followed by the genioglossus. Inferiorly, anterior to the vallecula in the glossoepiglottic space, the cornua of the hyoid bone are exposed at the lateral portions of the field. The lingual artery is again encountered as it courses over the hyoid, superiorly toward the inferolateral surface of the tongue before turning anterior. Dorsal lingual branches may be seen running medial toward the previously described arteriolar network. The hyoglossus muscle is seen lateral to the artery. Posteriorly, the artery is seen between the fibers of the hyoglossus and middle pharyngeal constrictor muscles. Anterior to the hyoglossus, the lingual artery splits into the deep lingual artery, which supplies the dorsal and lateral portions of the oral tongue, and sublingual artery, which supplies the ventral portion of the oral tongue and floor of the mouth. It is important to note that there is typically sufficient anastomotic flow from the lingual arteries to compensate for resection of one of the two with preservation of tongue tissues anterior to an ipsilateral resection. If at all possible, care should be taken to preserve at least one lingual artery. If resection of both arteries is necessary, the result will essentially be a total glossectomy, as there will not be enough blood supply to the tongue tissues anteriorly. Fig. 2.1c demonstrates this blood supply from a sagittal view. Fig. 2.4 depicts the steps for removal of a lateral BoT tumor.
Just lateral to the greater cornu of the hyoid and the lingual artery, on the lateral surface of the hyoglossus, the hypoglossal nerve can be identified medial to the submandibular gland as it courses superiorly and anteriorly to give motor innervation to the muscles of the tongue. It continues on the lateral surface of the genioglossus to innervate the muscles of the tongue. Care must be taken not to injure the hypoglossal nerve during the dissection, especially with electrocautery, as the hyoglossal fibers are neared. The lingual nerve may be encountered at the superior and lateral aspect of the resection, as it is running over the insertion of the styloglossus and portion of the superior constrictor muscle into the superior longitudinal muscle. It then runs forward along the dorsum of the tongue, supplying sensation and taste (via the chorda tympani nerve) to the anterior two-thirds of the tongue.
At the junction of the greater and lesser cornua and body of the hyoid, the attachments of the digastric tendon as well as the stylohyoid ligament can be identified. Hyoid attachment to the mandible is seen through the mylohyoid muscle laterally and inferiorly. The geniohyoid muscle is then identified anteriorly and superiorly. The inferior border of the hyoid bone will reveal attachments for the mylohyoid muscle.
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