Case l -  Cholecystitis with ultrasound correlation

Given the clinical concern for aortic dissection (this was performed soon after John Ritter died from a dissection, so our ED staff were hypervigilant regarding this daignosis), a CTA of the aorta was performed before lab results had returned.  You can tell this is an arterial phase scan.  Notice the cortical phase of enhancement in the kidneys.

The aorta and mediastinum are normal. The gall bladder is distended.  There is gall bladder wall edema.  The liver adjacent to the gall bladder is hyperemic. There may be some stranding in the surrounding fat (1, 2).  This constellation of findings is indicative of acute cholecystitis.  When the labs returned the patient has an elevated WBC.  LFT's were subsequently added on showing elevated transaminases normal bilirubin, and normal amylase.

Cholecystitis occurs when the cystic duct obstructs and there is stasis in the gall bladder.  This is the same pathophysiology seen in appendicitis.  As the pressure inside increases, the gall bladder becomes distended.  A distended gall bladder looks like a balloon being blown up.  It has no convex borders.  It is important to recognize that the gall bladder does not have to be enlarged to be distended.  It just needs to look tense, like a balloon, with convex walls throughout.

Examine the typical appearance of gall bladder wall edema.  There is a thin line of enhancing mucosa.  Do not get confused by this other line, which is the normal duodenal wall.  Peripheral to the musosa is a band of low attenuation which represents the thickened, edematous gall bladder wall.  Sometimes the mucosa will enhance briskly, exaggerating the contrast between it and the edematous wall.  Other times, like here, the difference is subtle. 

This appearance can also be seen with pericholecystic fluid, and the two can be difficult to differentiate.  For example, the edema here is indistinguishable from pericholecystic fluid.  However, pericholecystic fluid tends to remain in the space between the gall bladder and the liver.  Wall edema will also be seen in places where the gall bladder is bordered by duodenum or fat. When the abnormality is seen here (1, 2), away from the liver surface, the etiology is much more likely to be wall edema.

Pericholecystic stranding and hyperemia are more specific findings for cholecystitis and reflect inflammation in the surrounding fat and liver.  On this arterial phase scan the hyperemia is easy to see (1, 2, 3).  Scroll through the liver and see how this subtle rim of increased enhancement surrounds the gall bladder. Surrounding hepatic inflammation explains why patients with choelcystitis often have elevated transaminases.  Notice that there is no biliary dilatation.  Patients with cholecystitis usually do not have elevated bilirubin unless there is also a common duct obstruction.  This image nicely shows the common duct (blue) and normal pancreatic duct.

In this case the fat stranding (1, 2) is subtle and may just be volume averaging with the distended gall bladder.  Other cases will have better examples.

On ultrasound the equivalent findings are gall bladder distension, gall bladder wall edema, and a Murphy's sign.  The distended gall bladder looks like a taut balloon that is being inflated.  It does not flop back onto itself.  Remember, a distended gall bladder does not have to be large, just taut.  Hypoechoic wall thickening represents gall bladder wall edema, and can be focal.  It does not have to be circumferential.  However, the most specific finding on ultrasound for cholecystitis is a sonographic Murphy's sign: eliciting pain when pressing gently but focally on the gall bladder.  You should always perform this aspect of the scan yourself so you can differentiate this finding from generalized RUQ discomfort and/or a whiny patient.  Stones may or may not be present.   The stones in this gall bladder are seen on ultrasound but not on the  CT.

This patient had an emergent cholecystectomy and had acute cholecystitis.

Take home points:

• CT findings of cholecystitis are a distended gall bladder, gall bladder wall edema, surrounding fat stranding, and surrounding liver hyperemia.
• A distended gall bladder does not need to be large, just distended like a balloon being inflated.  It will not flop back onto itself.
• Patients with cholecystitis frequently have elevated transaminases and normal bilirubin.  Elevated LFT's are not necessary.  Elderly patients may not always have an elevated WBC.