The esophagus is a muscular tube that extends from approximately the level of the cricoid cartilage to its intersection with the stomach, known as the gastroesophageal (GE) junction. For clinical purposes, the distance to the GE junction is measured starting at the incisors and is generally about 25 cm in the adult.
Histologically, the esophagus consists of nonkeratinized squamous epithelium overlying lamina propria and submucosa. Beneath the submucosa is the muscularis propria, consisting of inner circular and outer longitudinal muscle layers. In the upper-third of the esophagus, the muscularis propria consists of striated muscle that gives way to smooth muscle in the middle and lower thirds. There is no serosa to the esophagus allowing for spread of tumor into the posterior mediastinum; additionally, the submucosa contains a dense lymphatic system that allows tumors to metastasize to distant sites (Figure 10-1).
Histology of normal esophagus. (A) Longitudinal section of esophagus shows mucosa consisting of nonkeratinized stratified squamous epithelium (SS), lamina propria (LP), and smooth muscles of the muscularis mucosae (MM). Beneath the mucosa is the submucosa containing esophageal mucous glands (GL) that empty via ducts (D) onto the luminal surface. ×40. H&E. (B) Transverse section showing the muscularis halfway along the esophagus reveals a combination of skeletal muscle (right) and smooth muscle fibers (left) in the outer layer, which are cut both longitudinally and transversely here. This transition from muscles under voluntary control to the type controlled autonomically is important in the swallowing mechanism. ×200. H&E. Source: Mescher AL. Junqueira’s Basic Histology Text and Atlas. 15th ed. New York, NY: McGraw-Hill; 2018. http://accessmedicine.mhmedical.com.
Developmental abnormalities involving the esophagus include atresia, fistulae, webs, and rings. Esophageal atresia occurs when there is incomplete separation between the trachea and esophagus, both of which develop from the primitive foregut, leading to incomplete formation of the esophagus. Frequently, esophageal atresia is accompanied by the development of fistula between the trachea and the esophagus. The most frequent anomaly is that of esophageal atresia with a distal tracheoesophageal fistula (Figure 10-2).
Other anatomic abnormalities of the esophagus are frequently secondary to a physical or environmental insult. Esophageal stricture/esophageal stenosis occurs when there is scarring of the esophageal wall following injury. Possible etiologies include gastroesophageal reflux disease (GERD), radiation/chemical injury (e.g., ingestion of alkaline substances such as lye), or autoimmune conditions such as scleroderma.