The case last time demonstrates a great example of a comet-tail artifact, which is a special type of reverberation artifact, related to micro-calicific or highly reflective objects interrogated by the ultrasound beam. In the case of the gallbladder, this is consistent with Adenomyomatosis, which is a common cause of focal or diffuse gallbladder wall thickening, due to cholesterol deposition and formation of Rokitansky-Aschoff Sinuses (intramural diverticula lined by mucosal epithelium) penetrating into the muscularis layer of the gallbladder wall. Generally, this is an asymptomatic, incidental finding and is not necessarily premalignant, but can be found in the setting of chronic gallbladder inflammation, which has a higher risk of gallbladder cancer.
There are three characteristic appearances on imaging of the related gallbladder wall thickening, which are fundal (focal), segmental (annular) , and generalized (diffuse), of which, fundal seems to be the most common. Radiopedia also has a nice example of the MRCP appearance of adenomyomatosis, as can be seen below.
Case courtesy of Dr Erik Ranschaert, Radiopaedia.org. From the case rID: 12339
