Cancer of the Hypopharynx and Cervical Esophagus

DANIEL J. KELLEY, MD

The management of malignant neoplasms of the hypopharynx and cervical esophagus remains difficult despite recent advances in surgical techniques as well as multidisciplinary treatment programs. Many patients present at a later age with advanced disease due to the occult nature of associated symptoms. The disease process and treatment often affect adjacent structures, such as the larynx. Regardless of the type of therapy employed, high recurrence rates, poor survival, and significant alterations in speech and swallowing function are a common experience for patients with malignancies in these anatomic sites. Despite these frustrations, patients are potentially curable and should be offered regimens that carefully consider morbidity and outcome within the context of the patient's overall medical condition.

ANATOMY

Malignant neoplasms of the hypopharynx and cervical esophagus are often discussed within the same context because of their anatomic proximity and similar clinical behavior. The pharynx is a muscular tube that extends from the base of the skull to the esophagus.1 It is arbitrarily divided into the nasopharynx, oropharynx and hypopharynx based on anatomic landmarks, although it is a continuous structure. The hypopharynx extends from the floor of the vallecula to the inferior border of the cricoid cartilage and is intimately associated with the larynx. It is continous with the oropharynx superiorly and the cervical esophagus inferiorly.

Within the hypopharynx, there are three anatomic subsites which are used to assess tumor stage. The pyriform sinus extends from the pharyngoepiglottic fold to the upper end of the esophagus at the lower border of the cricoid cartilage.2 The medial extent of the pyriform sinus includes the aryepiglottic folds, arytenoid, and cricoid cartilages and its lateral border is the inner surface of the thyroid cartilage.2 The post-cricoid region extends from the level of the ary-tenoid cartilages and connecting folds to the inferior border of the cricoid cartilage. Finally, the posterior pharyngeal wall is bounded superiorly by the floor of the vallecula superiorly and inferiorly by the inferior border of the cricoid cartilage.2

The walls of the pharynx consist of five layers from medial to lateral: mucosa, submucosa, pharyn-gobasilar fascia, muscular layer, and buccopharyn-geal fascia.1 The mucous membrane consists of columnar epithelium and is ciliated in some areas.1 The submucosa contains many small veins forming a venous plexus, mucous and minor salivary glands, and lymphoid tissue.1 The pharyngobasilar fascia is attached superiorly to the skull base and fills the gaps between constrictor muscles within the phar-ynx.1 The muscular layer at the level of the hypopharynx consists of the inferior constrictor, while the middle and superior constrictor form the more superior aspects of the pharynx. Finally, the buccopharyngeal fascia forms the outer layer of the pharynx.1 It is continuous with the visceral fascia of the esophagus and acts as the anterior boundary of the retropharyngeal space.1

The blood supply to the hypopharynx includes the ascending pharyngeal branch of the external carotid artery, the ascending palatine and tonsillar branches of the facial artery (external carotid artery) and the descending pharyngeal and palatine branches of the internal maxillary artery (external carotid artery).1 A plexus of veins located adjacent to the pharyngobasi-lar fascia drains into the internal jugular vein from the hypopharynx.1 Lymphatic fluid from the hypopharynx drains into retropharyngeal, jugular, and deep cervical lymph nodes.1 The pharyngeal branch of the vagus nerve provides motor innervation and the glossopharyngeal nerve provides sensory perception of the hypopharynx. Branches of the superior cervical sympathetic ganglion combine with branches of the glossopharyngeal and vagus nerve to form the pharyngeal plexus, which provides additional innervation to the hypopharynx.

The esophagus is a mucosa-lined muscular tube that serves as a conduit between the pharynx and the stomach. For the purposes of classification, staging, and reporting of cancer cases, it is divided into the following subsites: cervical, upper thoracic, mid-thoracic, and lower thoracic.2 Approximately 5 percent of cases of esophageal carcinoma arise within the cervical esophagus.3 The cervical esophagus extends from the inferior border of the cricoid cartilage to the thoracic inlet.2 The wall of the esophagus is comprised of an inner mucosa of squamous epithelium, a prominent submucosa, a muscular layer and an adventitia without serosa.2,4 The submucosa contains mucous glands, blood and lymphatic vessels, and a plexus of nerves.4 The muscular layer contains an inner circular layer surrounded by an outer longitudinal layer.4 Although the lower two-thirds of the esophagus is composed of smooth muscle, the most proximal end is exclusively striated and the remainder is mixed.5

The blood supply to the cervical esophagus comes from the inferior thyroid arteries. Branches of the thoracic aorta and bronchial arteries supply the thoracic portion. The cervical esophagus is innervated by cranial nerves IX and X, the cranial root of the spinal accessory nerve as well as sympathetic and parasympathetic fibers.4 The recurrent laryngeal nerve innervates the upper cervical esophageal muscles and contributes to the innervation of the cricopharyngeus muscle.6 As many as 8 to 14

branches of the recurrent laryngeal nerve are distributed along the esophagus and trachea.7 Lymphatics from the submucosa drain into paratracheal lower deep cervical and superior mediastinal lymph nodes.

The upper esophageal sphincter (UES) is located at the junction of the hypopharynx and cervical esophagus. It is composed of three muscles: inferior pharyngeal constrictor (IPC), cricopharyngeus (CP) and cervical esophagus (CE).6 The CP is strategically located between the pharynx and esophagus and is responsible for the high-pressure zone of the UES.8 All three muscles contract to maintain tone in the UES, but only the CP relaxes in response to physiologic stimulus.9 These muscles also differ based on the pattern of motor end plates, proportion of fastand slow-twitch muscle fibers, and their innervation. These differences suggest different roles during swallowing. The physiologic low-pressure zone of the cervical esophagus is composed of equal amounts of striated and smooth muscle, and is located about 5 cm from the proximal portion of the cricopharyngeus muscle.5 Esophageal distension, pharyngeal pressure and inflation of the lungs contract the CP and UES via vago-vagal and glossopharyngo-vagal reflexes.9 The UES or CP also contracts with arousal or with changes in posture.9 These reflexes, along with the elastic properties of the CP, contribute to the generation of tone in the CP and UES.

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