Sphincter of Oddi 

-Found at the confluence of the distal CBD and the pancreatic duct as they enter the duodenum
-Usually during fasting, the Sphincter of Oddi allows bile to be released into duodenum via contractions and working with the MMC (migratory motor complex)
-When this does NOT happen, you can get SOD

SOD is also known as:

-Biliary Spasm
-Biliary dyskinesia
-Papillary stenosis
-Post-cholecystectomy syndrome 

Two main diseases that SOD can cause

-Biliary pain
-Idiopathic recurrent acute pancreatitis

Epidemiology and Clinical manifestations

-Usually seen in middle aged women who have undergone cholecystectomy (not always)
-Presents as  biliary pain , usually RUQ/Epigastric, lasting 30 minutes-hours
-Labs show elevated AST/ALT/ALK that can normalize between attacks, CBD dilated > 8 mm with normal amylase/lipase
–Rome IV Criteria (+ Biliary pain, no bile duct stones/structural abnormalities, elevated liver enzymes or dilated bile ducts but NOT both)

What is a normal CBD?

-95 % normal patients with CBD < 6 mm but increases with age (~upper limit corresponds to decade of life)
–Can see CBD up to 10 mm post-cholecystectomy

How do you make the diagnosis?

It is a diagnosis of exclusion!! 

-Exclude IBS (do symptoms get better/worse with constipation/diarrhea)
-Start with LFT and pancreatic enzymes (rule out pancreatitis)
-Next check transabdominal ultrasound (rule out stone)
-Then MRCP vs. EUS/ERCP (is there a Structural issue?)
-Hepatobiliary scintigraphy
-Best way to diagnose it is via Sphincter of Oddi manometry for definite diagnosis. 

Treatment

-Medical treatment (not great)- smooth muscle relaxers, CCB, nitrates
-Surgical treatment: Endoscopic sphincterotomy, ultimately may need surgery for biliary and pancreatic sphincterotomy