Mel, get the HIDA/CCK! I had four (4) (I kid you not -- 4) "Normal" sono's that indicated my GB was "normal." However, the HIDA showed that my GB is anything but "normal!" For the first 4 hours it did not image. Then, after they gave me a shot of morphine (to cause it to contract) it still took almost an hour to light up. Finally, once they established I do indeed have a GB, they gave me the CCK and the ejection factor was 21% (doc said 42% is low average). So, next stop is the surgeon. That said, last Spring my husband (normal GB ultrasound) had a HIDA that was only 17% -- they took out his GB and while testing the "seal" on the reconnect, noticed a stricture on his Common Bile Duct. One ERCP later, he was finally once and for all cured. (He's a happy, happy man!)
Meanwhile, my Gastro recommended a no fat/low fat diet while I wait for the surgical consult. The best diet I've found is on docsmed.com by Dr. Smedley. (His theory that anoxeria is related to GB disease is a little unconventional but I've found him to be 100% on-the-money about what not to eat to avoid an attack.) The only thing I've changed in the 6+weeks I've followed it is to add corn* to the foods to avoid and delete even the 1 tbs of fat a day. Basically, I've been surviving on lettuce, cooked spinich, baked potatos, grilled chicken, lemon tuna, grapenuts cereal, strawberries, peaches and the occassional handful of raisans or seedless grapes. Deviating results in pain.
*through trial-and-error I discovered corn, especially corn-on-the-cob gives me pain even though I was eating lots of corn flakes without a problem.
If I were a betting man I'd say you have some kind of gallbladder dysfunction, most likely gallstones from what you say. Have they run an Ultrasound? Before they do the HIDA/CCK they should REALLY do the ultrasound. If that comes out normal, and you don't have gallstones, then the HIDA will likely show that you have gallbladder dyskinesia.
I had the same thing for a year and finally went to a doctor that took an ultrasound and found that I had gallstones and needed an operation. Just had the operation done last week and feel great. Get the ulatrasound.
If the pain occurs mainly after the fatty meal, then its probably related to gallbladder, and having a HIDA scan is good decision.
Avoid fatty meals to avoid pain.