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Diagnostics
Disease
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Diagnostic Procedures A number of common laboratory assays can be used to help narrow the diagnosis in biliary disease, and exclude other sources of pain in the abdomen. Alkaline Phosphatase is a marker of cholestasis. In fact, greater than 90% of patients with bile stasis will have an elevated alkaline phosphatase. However, because isozymes of alkaline phosphatase are found in the liver, bone, placenta, and small intestine, an elevated alkaline phosphatase, alone, is not specific for biliary disease. Bilirubin is the breakdown product of heme, with the majority coming from senescent RBC's and (to a lesser extent) from cytochromes and myoglobin. Unconjugated bilirubin is hydrophobic and transported in the blood (reversibly) bound to albumen. It is taken up by liver cells, converted to conjugated bilirubin, and actively secreted into the biliary canaliculi. Bilirubin and alkaline phosphatase are used together to evaluate evidence of common duct obstruction. Aminotransferases (ALT and AST) are found in the liver, cardiac, and skeletal muscles. ALT is found predominantly in the cytosol of hepatocytes, and an elevated ALT is more likely to suggest liver injury. AST, on the other hand, is found in both the cytosol and mitochondria, and elevated levels typically point to hepatocellular injury sustained over a longer period of time (weeks). The aminotransferases are used to evaluate the presence of hepatitis and may be elevated in cholecystitis or with common bile duct obstruction. Amylase and Lipase are commonly ordered on the patient presenting with abdominal pain. They are used to help exclude pancreatitis as a cause, however, amylase may also be mildly elevated in cholecystitis. Urinalysis is typically used to rule out pyelonephritis and renal calculi as a source of abdominal pain. Pregnancy Testing should be done on all women of child bearing age.
Because gallstones are only radiopaque and seen on plain film x-rays in 10-30% of cases, ultrasound has become the diagnostic procedure of choice when evaluating right upper quadrant pain. It is a fast, cheap, and non-invasive way to look at the biliary system and gain insightful information when narrowing a diagnosis. It is particularly good at detecting gallbladder disease and biliary dilatation. Ultrasound uses technology similar to sonar. A two-dimensional image of echoes is created with fluid appearing black, solid organs appearing hypoechoic, and structures with high amounts of fat or minimal water appearing hyperechoic. Gallstones appear as a highly echogenic focus with acoustic shadows and move to a dependant portion of the gallbladder. Ultrasound can detect stones as small as 1-2mm and has a sensitivity on the order of 95% and a specificity of about 97%. The presence of a thickened gallbladder wall, pericholecystic fluid, and a sonographic Murphy sign (pain elicited when the ultrasound is pressed into the RUQ on inspiration) supports the diagnosis of cholecystitis. Because of the interference with bowel gas, ultrasound has limited capacity in evaluating the common bile duct, and may miss 25-40% of bile duct stones.
Cholangiography can be used both intra- and extra-operatively to help visualize the biliary system. Intra-operative cholangiograms (IOC) are typically performed during cholecystectomy when there is clinical evidence that a stone may be present in the common bile duct, however, some surgeons tend to perform IOC's during any and all cholecystectomies. Extra-operatively, endoscopic retrograde cholangiopancreatography (ERCP) is an invasive endoscopic procedure in which radiopaque contrast is injected into the biliary ductal system under fluoroscopic guidance. During intra-operative cholangiography, the contrast is delivered directly into the cystic duct once clamped from the gallbladder during cholecystectomy. The biliary system (in both cases) can then be imaged to see if filling defects exist between the gallbladder and the small bowel (that is, whether stones are impacted in the common bile duct (choledocholithiasis) or at the Sphincter of Oddi).
Hepatobiliary scintography (HBS) uses hepatoiminodiacetic acid (HIDA) or diisopropyl iminodiacetic acid (DISIDA) in order to study the biliary system. This test should be ordered when acute cholecystitis is suspected, as it has been found to be 95% accurate in diagnosing acute cholecystitis. Nonvisualization of the gallbladder supports the diagnosis of acute calculous cholecystitis with a sensitivity and specificity around 95%. It can also be used to confirm the presence of a biliary leak. In a typical study, the gallbladder, common bile duct, and small bladder should fill within 30-45 minutes. The addition of IV morphine can improve the accuracy of the scan if the gallbladder is not visualized. Morphine works by increasing the resistance to flow through the Sphincter of Oddi, resulting in filling of the gallbladder.
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