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Sphincter of Oddi Dysfunction
The sphincter of Oddi (SO) is a smooth muscular structure usually 7 to 13 mm in length encircling the distal common bile duct (CBD) and the pancreatic duct (a common channel opening into the ampulla of Vater). The three functions of the SO are control of the flow of bile and pancreatic secretions into the duodenum, prevention of reflux of duodenal juice into the pancreaticobiliary system, and regulation of gall bladder function. Papillary stenosis refers to the type of SO dysfunction (SOD) related to a structural abnormality. Biliary dyskinesia is a functional blockage at the high-pressure zone attributed to spasm and/or hypertrophy or neuropathy of the sphincteric nerves. The advent of biliary manometry has contributed to a better understanding of the SO functions. The “gold standard” in evaluating SO dysfunction is manometry, which is invasive because it needs an endoscopic retrograde cholangiopancreatography (ERCP) setting.
Anatomy and Physiology
The SO is composed of a biliary and a pancreatic sphincter. The common ductal segment passes obliquely through the duodenal wall and terminates at the papilla of Vater, a small nipplelike protrusion less than 1 cm in diameter. Numerous variations are observed as the common bile and pancreatic ducts join ( Figs. 139.1 and 139.2 ). The sphincter function is regulated by neuronal and hormonal factors.
The SO has a rich supply of nerves—intrinsic catecholamine-containing neurons, nonadrenergic noncholinergic (NANC) including substance P, vasoactive intestinal peptide (VIP), somatostatin, calcitonin gene–related peptide, met-enkephalin-like immunoreactivity, prominent galanin-like immunoreactivity, and nitric oxide—most of which play a role in SO function. Spontaneous motor activity of the SO is primarily myogenic in nature and is presumed to be regulated by interstitial cells of Cajal. During the fasting stage, SO motility is integrated with migrating motor complex, which alters the flow of bile into the duodenum. The basal pressure of SO is 15 mm Hg (3–35 mm Hg). The duodenal hormone cholecystokinin that contracts the gallbladder also relaxes the SO.
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