Case x -  Introduction to cholecystitis

The gall bladder is distended.  There is gall bladder wall edema, adjacent fat stranding (1, 2), and adjacent hepatic hyperemia (1, 2, 3).  The findings indicate acute cholecystitis.

This case nicely demonstrates gall bladder wall edema.  The mucosa of the gall bladder is a thin enhancing stripe.  The edematous wall is the low attenuation strip seen peripherally.  This is very well demonstrated on the coronal images: mucosa, edema.  The case also demonstrates the difference between pericholecystic fluid and gall bladder wall edema.  The two can look identical.  When the fluid is constrained to the space between the gall bladder and liver it can be either wall edema or pericholecystic fluid and you cannot differentiate.  However, when fluid is seen in areas not adjacent to liver parenchyma, the finding represents wall edema.

This case also nicely demonstrates pericholecystic hepatic hyperemia (1, 2, 3).  The liver immediately surrounding the gall bladder shows more enhancement than the rest of the liver.  This is very well shown on the coronal image using the narrow liver windows.  Hyperemia is best seen on arterial phase images since it is due to increased arterial flow.  Portal flow is unchanged so the parenchyma becomes isodense on more delayed images.  Hyperemia is a response to inflammation.  Since there is liver inflammation you might expect elevated liver enzymes.  Some cases of acute cholecystitis do have accompanying elevations in AST, ALT, and alkaline phosphatase.  However, it is uncommon to have an elevated bilirubin.  While cholecystitis is secondary to obstruction of the gall bladder, it is uncommon to have obstruction of the biliary tree.  Notice that there are no dilated intrahepatic biliary ducts.  The common duct is also not dilated.

The pericholecystic fat stranding is not prominent but is present.  There is increased density in the fat immediately surrounding the gall bladder fundus (1, 2).

As an anatomic exercise, notice the position of the common duct in the head of the pancreas.  You should be able to follow the common duct superiorly into the liver on most CT examinations.  Review several of the previous cases and try to find the common duct on each one.

Each individual finding is not specific for cholecystitis.  The constellation of findings are.  When CT imaging is inconclusive or seems contrary to the stated history then an ulrasound can be performed.  Ultrasound allows a second look at the gall bladder wall and allows you to assess for point tenderness over the gall bladder.  This will be discussed in a separate case. If CT and ultrasound contradict each other, a nuclear medicine gall bladder scan can be performed.

Did you notice the normal appendix.   It is hard to find.  It may contain a punctate appendicolith.

Take home points:

• Findings of cholecystitis are a distended gall bladder, gall bladder wall edema, pericholecystic stranding, and pericholecystic hepatic hyperemia.
• Understand the appearance of gall bladder wall edema on CT: low attenuation peripheral to enhancing mucosa.
• WBC, AST and ALT may be elevated but do not have to be.  Bilirubin is rarely elevated.
• Ultrasound and nuclear medicine scan are useful confirmatory examinations.