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Abstract
It is claimed that the right diaphragmatic crus forms a loop sphincter arround the lower esophagus. We investigated the hypothesis that the loop-shaped muscle does not belong to the diaphragmatic crura either anatomically or physiologically and is considered an autonomous muscle. Thirty-two cadaveric specimens (20 males, 12 females, 22 adults, mean age 36.2 ± 11.8 years, 10 mature neonatal deaths) fixed in 10% formalin were studied anatomically. Electrophysiologic study was performed in 14 subjects (8 men, 6 women, mean age 36.6 ± 8.2 years) scheduled for laparatomy. The loop muscle was stimulated by needle electrode, and response from the muscle and right crus was recorded by two electrodes. The test was repeated using an electrode into the left crus. Response of the loop muscle to individual stimulation of right and left crus was also registered. Muscle bundles formed a U-shaped loop around the lower esophagus, with the two limbs inserted into the 1st lumbar vertebra. An “esophago-sphincteric space” existed between the two limbs anterior to the esophagus. Three patterns of loop insertion were identified: classic, limb fusion, and limb crossing. The two crura were tendinous from their vertebral attachment, became fleshy, and fanned out proximally to merge with the fleshy diaphragm proper. Stimulation of loop muscle affected significant increase of its electric activity but had no effect on right or left crus. Crural stimulation produced significant increase of their electric activity and no effect on the loop muscle. Muscle fibers surrounding the lower esophagus formed a U-shaped loop. The loop arrangement seems to play significant role in competent mechanism of the gastroesophageal junction. Anatomic and electrophysiologic evidence suggest that the loop muscle is an autonomous muscle that surrounds the lower esophagus and is not derived from the diaphragmatic crura. We call this muscle “striated gastroesophageal sphincter.”