Focal diffuse gallbladder wall thickening with comet tail reverberation aifacts on USG is seen in the following condition:

Adenomyomatosis is a type of hyperplastic cholecystoses, characterized by a benign proliferation of gallbladder surface epithelium with glandlike formations, extramural sinuses, transverse strictures, and/or fundal nodule ("adenoma" or "adenomyoma") formation. The classic appearance is focal wall thickening in the gallbladder fundus. The presence of cystic spaces and echogenic foci with "comet tail" reverberation aifact is diagnostic of adenomyomatosis. Ref: Longo D.L., Fauci A.S., Kasper D.L., Hauser S.L., Jameson J.L., Loscalzo J. (2012). Chapter 311. Diseases of the Gallbladder and Bile Ducts. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.