Figure 2 - Anatomic radiographic landmarks of the lower esophageal sphincter (LES).

Normally, in between swallows, the LES remains closed. With a barium swallow the LES opens and its identity is lost unless some constriction lesions are present. For example, the anatomic inferior esophageal sphincter may be identified as a muscular ring (also known as contractile ring or A ring) or mucosal ring (also called Schatzki's ring or B ring) located at the squamocolumnar junction. Usually the squamocolumnar junction forms a zigzag line without a constriction in which case the lowermost part of the LES cannot be identified. Note that a relaxed LES can open wider than the esophageal body itself and has been called a vestibule by the anatomists and an ampulla by the radiologists. ESO, esophagus. (Source: Goyal RK. The lower esophageal sphincter. Viewpoints on Digestive Diseases. Am Gastroenterol Assoc 1976;8(3), with permission.)