MIRIZZI SYNDROME GALLBLADDER ENLARGEMENT

Mirizzi syndrome is a rare cause of biliary obstruction in which the cystic duct is obstructed by a stone, which in combination with a surrounding inflammatory process compresses and obstructs the common hepatic duct, causing distal biliary duct dilatation. This is associated with a low insertion of the cystic duct into the common hepatic duct. Occasionally a fistula forms between the hepatic duct and the gallbladder due to erosion of the duct wall by the stone. Ultimately this may lead to gallstone ileus—small-bowel obstruction resulting from migration of a large stone through the cholecystoenteric fistula. If the condition is not promptly diagnosed, recurring cholangitis leading to secondary biliary cirrhosis may result. On ultrasound the gallbladder may be either enlarged or contracted and contain debris. A stone impacted at the neck may be demonstrated together with dilatation of the intrahepatic ducts with a normal-calibre lower common duct. The diagnosis, however, is difficult, and ERCP is generally the most successful modality. Although rare, it is an important diagnosis as cholecystectomy in these cases has a higher rate of operative and postoperative complications.

ENLARGEMENT OF THE GALLBLADDER
Because of the enormous variation in size and shape of the normal gallbladder, it is not possible to diagnose pathological enlargement by simply using measurements. Three-dimensional techniques may prove useful in assessing gallbladder volume6 but this is a technique which is only likely to be clinically useful in a minority of patients with impaired gallbladder emptying. An enlarged gallbladder is frequently referred to as hydropic. It may be due to obstruction of the cystic duct or associated with numerous disease processes such as diabetes, primary sclerosing cholangitis, leptospirosis or in response to some types of drug. A pathologically dilated gallbladder, as opposed to one which is physiologically dilated, usually assumes a more rounded, tense appearance.

Mucocoele of the gallbladder
If the cystic duct is obstructed, usually by a stone which has failed to pass through to the CBD, the normal flow of bile from the gallbladder is interrupted. Chronic cystic duct obstruction causes the bile to be replaced by mucus secreted by the lining of the gallbladder, resulting in a mucocoele. The biliary ducts remain normal in calibre. If the gallbladder looks dilated, make a careful search for an obstructing lesion at the neck; a stone in the cystic duct is more difficult to identify on ultrasound as it is not surrounded by echo-free bile.